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Abstract Bathochromic shift‐type OHC (b‐OHC) was found in donor–acceptor (D–A) type pyridinium dye bearing halide ion as a counter anion, as well as donor‐π‐acceptor (D‐π‐A) type pyridinium dye; the intramolecular charge transfer‐based photoabsorption maxima (λ_max^abs) in halogenated solvents show a large bathochromic shift, in comparison with those in non‐halogenated solvents. It was revealed that there is a good relationship between the most positive surface electrostatic potential (V_S,max) values associated with the most positive σ‐hole on halogen atoms in organohalogen molecule and the λ_max^abs, indicating that the b‐OHC of the D–A and D‐π‐A pyridinium dyes is attributed to the formation of halogen bond (XB) or complex such as [R─X·Y]⁻ between the halogen atom (X) of organohalogen molecule and the counter anion (Y) of dye molecule. Moreover, the plots of the λ_max^abs against the V_S,max values demonstrated that the b‐OHC characteristic of D–A pyridinium dye is lower than that of the D‐π‐A pyridinium dye. It was suggested that the formation of XB induces a decrease in the ring current of the pyridinium ring, that the LUMO is mainly localized, resulting in the expression of b‐OHC. Consequently, this work offers a deeper insight into the mechanism for the expression and the origin of OHC.

Abstract Phenazinone chromophore incorporating a carbonyl group into the skeleton is recently found to be a new‐type halogen‐atom‐free‐photosensitizer possessing superior ability in singlet oxygen (¹O₂) generation. In this work, in order to gain insight into the substituent effect on the optical properties and ¹O₂ generation ability of phenazinone‐based PSs, we have designed and developed the derivative with two 5‐formyl‐2‐thienyl substituents which is expected to lead to improvement of the light harvesting and ¹O₂ generation efficiencies. This work revealed that the introduction of 5‐formyl‐2‐thienyl substituents into phenazinone chromophore leads to bathochromic shift of photoabsorption band, but to a thermodynamically unfavorable energy gap (ΔE_ST) value between the S₁ state and the T_n state as well as a low intersystem crossing (ISC) constant (k_ISC), resulting in the low ¹O₂ quantum yield, although the phenazinone chromophore possesses thermodynamically feasible ISC characteristics based on El‐Sayed's rule.

Abstract Functional dyes exhibit intriguing properties in response to external stimuli related to their optical, electronic, structural, and energetic characteristics and enable unique stimuli-responsive functions in materials by collaborating with polymers, particularly when chemically incorporated into the polymer structures. As well as the structures and properties of functional dyes, polymers, assemblies, and materials, the interactions between these components are important to the functions of materials. In this review, we introduce our recent studies conducted in the past half decade on stimuli-responsive smart polymers and polymeric materials based on functional dyes that are chemically incorporated into the polymer structures, with a special focus on light, force, electric fields, and chemicals including water in a variety of external stimuli. For example, these polymers and materials offer switchable adhesion, mechanical actuation, and chemical sensing.

In this study, we synthesized polymer composites by incorporating polyhedral oligomeric silsesquioxane (POSS) units into polythiophene to reduce the thermal conductivity of conductive polymers. The synthesized polymers were copolymers with various POSS incorporation rates, reflecting the monomer feed ratios. Introduction of POSS units proved highly effective in reducing the thermal conductivity of the polymer films by more than half and improving the Seebeck coefficient, although it markedly reduced the electrical conductivity. This composite approach shows promise in reducing the thermal conductivity of conductive polymers, suggesting the need for further research to improve electrical conductivity.

This work provides facile synthetic methods for 1,1′,3,3′-tetraaryl-4,4′-bibenzo[c]thiophene derivatives with the same or different aryl substituents on the thiophene rings and useful methods to adjust their optical and electrochemical properties.

Cyano-substituted phenazine-2,3-diol-based dyes, YC-1 and YC-2, which have n-hexyl and formyl groups, respectively, on thiophene units, have been newly developed as halogen-atom-free-heteroanthracene-based photosensitizers (PSs) possessing the ability to generate singlet oxygen (1O2). The photoabsorption edge (λabsedge) of YC-1 reached 700 nm which is in a longer wavelength region by 50 nm in comparison with that (650 nm) of YC-2. However, the λabsedge of YC-1 and YC-2 exhibited blue-shifts, compared to those (700 nm and 800 nm) of nitro-substituted phenazine-2,3-diol-based dyes KI-3 and KI-5 with formyl groups and the n-hexyl group, respectively, in our previous work. KI-3 and KI-5 show low fluorescence and 1O2 generation quantum yields (Φfl < 0.01 and ΦΔ = 0.05 and 0.02, respectively), which are due to the rapid nonradiative decay of the excited states by the nitro group. YC-1 and YC-2 exhibited also feeble fluorescence with low Φfl values (<0.01 and 0.022, respectively), meanwhile YC-2 showed a moderate ΦΔ value (0.29) but the ΦΔ value (0.0081) of YC-1 was significantly lower than those of the other PSs. Time-dependent density functional theory (TDDFT) calculations revealed that YC-2 with the formyl groups has the smallest energy gap ΔEST (−0.05 eV) between the S1 (ππ*) state and the Tn state with nπ* characteristics among these PSs (−0.12 eV for KI-3, −0.36 eV for KI-5, and −0.24 eV for YC-1), leading to efficient intersystem crossing (ISC) according to the El-Sayed rule. In addition, it was suggested that the low ΦΔ value of YC-1 with n-hexyl groups is due to the relatively large ΔEST value as well as the flexible n-hexyl groups which accelerate internal conversion (IC) from the S1 to S0 state, as evidenced by the low Φfl values, resulting in inferior ISC. Consequently, we demonstrated that cyano-substituted phenazine-2,3-diol-based PSs reduce the rapid nonradiative decay of the excited states and the ΔEST values, leading to efficient ISC for 1O2 generation, compared to nitro-substituted phenazine-2,3-diol-based PSs.

We developed phenazine-2,3-diol-based photosensitizers bearing carboxylic acid salts which possess high solubility and moderate ¹O₂ generation ability in water.

Benzo[c]thiophene and its derivatives are attractive chromophores or π-building blocks for emitters, photosensitizers, and semiconductors used in organic optoelectronic devices. Herein, we provide facile synthetic methods of 1,1′-diaryl-4,4′-bibenzo[c]thiophene derivatives by Stille or Suzuki coupling reaction and their photophysical properties in the solution and the solid state, electrochemical properties, and X-ray crystal structures.

Phenazinone derivatives PZ1-3 where a carbonyl group is incorporated into the chromophore are designed and developed as halogen-atom-free-heteroanthracene-based photosensitizers possessing the ability to generate singlet oxygen (O-1(2)). Compared to the phenazine-2,3-diol (PZ) without a carbonyl group, the molar absorption coefficients of PZ1-3 at around 480 nm increased by a factor of five to six. Furthermore, the values of fluorescence quantum yields (phi(fl)) of PZ1-3 were significantly low (0.03 for PZ1, 0.04 for PZ2, and 0.05 for PZ3). To evaluate the O-1(2) generation ability of PZ1-3, the O-1(2) quantum yields (phi(delta)) of PZ1-3 were estimated and it was demonstrated that PZ1 exhibited a higher phi(& UDelta;) value than rose bengal (RB) known as a reference photosensitizer to generate O-1(2) (0.86 for PZ1, 0.54 for PZ2, 0.069 for PZ3, and 0.68 for RB). Moreover, the rate constants (k(r), k(nr), k(ISC), and k(IC)) of PZ1-3 indicated that the reason for the low phi(& UDelta;) of PZ2 and PZ3 comes from the vibrational relaxation caused by a flexible methoxymethoxy and 4-chlorobenzoate group, respectively. Density functional theory (DFT), time-dependent DFT (TD-DFT), and natural transition orbital (NTO) calculations suggested that for PZ1-3, the intersystem crossing (ISC) processes from the lowest excited singlet state (S-1) to the third triplet state (T-3) are thermodynamically feasible and facilitated based on El-Sayed's rule. Consequently, we propose that the phenazinone skeleton is one of the promising halogen-atom-free-heteroanthracene-based chromophore photosensitizers.

In this study, freestanding poly( 3, 4ethylenedioxythiophene): poly( styrene sulfonate) (PEDOT:PSS) films modified with an ionic liquid (IL) were synthesized assuming modulization. These films were easily peeled off the glass substrate in water, producing hydrophobic and flexible freestanding films that exhibited extremely high mechanical strengths. The thermoelectric properties of the IL-doped PEDOT:PSS films depended on the amount of IL incorporated. To analyze the mechanism of this dependence in detail, the compositions, higher-order structures, and electronic states of the polymer films were studied by X-ray photoelectron spectroscopy, X-ray diffraction analysis, and electronic absorption spectroscopy. In addition, the carrier density in the polymer film was quantified using electrochemical techniques, and its correlation with the thermoelectric conversion properties was analyzed.

In order to elucidate a detection mechanism of a photo-induced electron transfer (PET)-type fluorescent sensor for water, we have synthesized anthracene-(aminomethyl)-4-cyanophenylboronic acid (AminoMeCNPhenylB(OH)(2)) TF-2 by the deprotection of pinacol ester (Pin) of anthracene-AminoMeCNPhenylBPin OF-2. For OF-2, the PET takes place from the nitrogen atom of the amino moiety to the photoexcited fluorophore (anthracene) skeleton in the absence of water, leading to fluorescence quenching (PET active state). When water was added to the OF-2 solution, a drastic enhancement of the fluorescence emission is observed due to the formation of the PET inactive (fluorescent) species OF-2W or OF-2WH by interaction with water molecules which has been determined by H-1 NMR spectral measurements. On the other hand, even in the absence of water TF-2 exhibits intense fluorescence emission and addition of water to the TF-2 solution shows a negligible change in the fluorescence intensity. The H-1 NMR spectra of the TF-2 solution without the addition of water clearly indicated the formation of the PET inactive (fluorescent) species TF-2H by the intramolecular OH center dot center dot center dot N hydrogen bonding between the hydroxyl group of the B(OH)(2) moiety and the nitrogen atom of the amino moiety. For TF-2, single-crystal X-ray structural analysis as well as density functional theory (DFT) calculations revealed the existence of the intramolecular OH center dot center dot center dot N hydrogen bonding, that is, the formation of TF-2H. Interestingly, the H-1 NMR spectra of the TF-2 solution with the addition of water showed the existence of the PET inactive (fluorescent) species TF-2W or TF-2WH by interaction with water molecules, as with the case of OF-2. Consequently, it was found that for the PET-type fluorescent sensor based on the anthracene-AminoMeCNPhenylBPin structure, the BPin moiety is essential not only to activate the PET in the absence of water, leading to fluorescence quenching, but also to form the PET inactive (fluorescent) species upon the addition of water. This work provides a direction in molecular design toward creating an effective PET-type fluorescent sensor for water as well as a conclusive detection mechanism of the anthracene-AminoMeCNPhenylBPin structure for water.

As fluorescent materials for visualization, detection, and quantification of a trace amount of water, we have designed and developed a PET (photo-induced electron transfer)-type fluorescent monomer SM-2 composed of methyl methacrylate-substituted anthracene fluorophore-(aminomethyl)-4-cyanophenylboronic acid pinacol ester (AminoMeCNPhenylBPin) and achieved preparation of a copolymer poly(SM-2-co-MMA) composed of SM-2 and methyl methacrylate (MMA). Both SM-2 and poly(SM-2-co-MMA) exhibited enhancement of the fluorescence emission with the increase in water content in various solvents (less polar, polar, protic, and aprotic solvents) due to the formation of the PET inactive (fluorescent) species SM-2a and poly(SM-2-co-MMA)a, respectively, by the interaction with water molecules. The detection limit (DL) of poly(SM-2-co-MMA) for water in the low water content region below 1.0 wt% in acetonitrile was 0.066 wt%, indicating that poly(SM-2-co-MMA) can act as a PET-type fluorescent polymeric sensor for a trace amount of water in solvents, although it was inferior to that (0.009 wt%) of SM-2. It was found that spin-coated poly(SM-2-co-MMA) films as well as 15 wt% SM-2-doped polymethyl methacrylate (PMMA) films produced a satisfactory reversible fluorescence off-on switching between the PET active state under a drying process and the PET inactive state upon exposure to moisture, which is demonstrated by the fact that the both the films are similar in hydrophilicity to each other from the measurement of the water contact angles on the polymer film surface. Herein we propose that PET-type fluorescent polymer films based on a fluorescence enhancement system are one of the most promising and convenient functional dye materials for visualizing moisture and water droplets.

Lithium-ion batteries (LIBs) with silicon anodes have higher charge-discharge capacities than those with graphite anodes; however, the repeatabilities of their charge-discharge cycles are extremely low. Recently, silicon/graphene composites have been used in LIBs, but their complex synthesis inhibits the industrial applications of such LIBs. In this study, silicon/graphene composites were synthesized via a simple, environmentally friendly method using tetraethyl orthosilicate and natural graphite as inexpensive starting materials. The resulting composites were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis, which confirmed similar silicon/carbon atomic ratios in the composites and starting materials. When these composites served as an LIB anode material, the manufactured batteries showed charge-discharge capacities and charge-discharge cycle characteristics superior to those of graphene-anode-based and siliconanode-based batteries, respectively. They also showed performances comparable or superior to those of LIBs fabricated by costly, complicated conventional methods.

The (D-pi)2-type fluorescent dye OTT-2 with two (diphenylamino)carbazole-thiophene units as D (electron-donating group)-pi (pi-conjugated bridge) moiety and the (D-pi)2Ph-type fluorescent dye OTK-2 with the two D-pi moieties connected through a phenyl ring were derived by oxidative homocoupling of a stannyl D-pi unit and Stille coupling of a stannyl D-pi unit with 1,3-diiodobenzene, respectively. Their optical and electrochemical properties were investigated by photoabsorption and fluorescence spectroscopy, time-resolved fluorescence spectroscopy, cyclic voltammetry (CV) and molecular orbital (MO) calculations. In toluene the photoabsorption and fluorescence maximum wavelengths (lambda max,abs and lambda max,fl) of OTT-2 appear in a longer wavelength region than those of OTK-2. The fluorescence quantum yield (phi fl) of OTT-2 is 0.41, which is higher than that (phi fl = 0.36) of OTK-2. In the solid state OTT-2 shows relatively intense fluorescence properties (phi fl-solid = 0.24 nm), compared with OTK-2 (phi fl-solid = 0.15 nm). CV results demonstrated that OTT-2 and OTK-2 exhibit a reversible oxidation wave. Based on photoabsorption, fluorescence spectroscopy and CV for the two dyes, it was found that the lowest unoccupied molecular orbital (LUMO) energy level of OTT-2 is lower than that of OTK-2, but OTT-2 and OTK-2 have comparable highest occupied molecular orbital exhibits not only a bathochromic shift of the photoabsorption band, but also intense fluorescence emission both in solution and the solid state.

As a fluorescent sensor for water over a wide range from low to high water content regions in organic solvents, we designed and developed a PET (photo-induced electron transfer)/AIE (aggregation-induced emission)-based fluorescent sensor EN-1 composed of a tetraphenylethene (TPE) core and four anthracene-(aminomethyl)-4-cyanophenylboronic acid pinacol esters (AminoMeCNPhenylBPin) as peripheral units. EN-1 showed an enhancement of the fluorescence band at around 450 nm originating from the anthracene skeleton with increasing the water content in THF in the low water content region below 1.0 wt%, which was attributed to the formation of the PET-inactive (fluorescent) species EN-1(H2O) by the addition of water molecules. With increasing the water content from 10 wt% to 50 wt%, the fluorescence intensity at around 500 nm originating from the TPE core gradually increased, which was attributed to the restricted intramolecular rotation (RIR) of TPE due to the increase in the viscosity of the THF-water mixtures. Furthermore, a significant enhancement of the fluorescence band at around 470 nm in the water content region above 60 wt% was observed due to the AIE characteristics associated with the aggregate formation of EN-1(H2O)-A in both PET-inactive and RIR states. The detection limit (DL) of EN-1 for water in the low water content region below 1.0 wt% in THF was 0.21 wt%, which was superior to that (DL = 0.49 wt%) of RS-1 composed of a TPE unit and an anthracene-AminoMeCNPhenylBPin unit. Moreover, the AIE characteristics of EN-1 were observed from the relatively low water content of 60 wt% compared with those of RS-1, which were observed in the high water content region over 75 wt%. The improvement of the DL value and AIE characteristics of EN-1 was ascribable to the fact that the four anthracene-AminoMeCNPhenylBPin units led to increased fluorescence emission originating from the anthracene skeleton and its low solubility in solvent-water mixtures, compared with RS-1. Consequently, this work reveals that EN-1 composed of a TPE core and four anthracene-AminoMeCNPhenylBPin units can act as a PET/AIE-based fluorescent sensor for the detection of water in a low water content region and from moderate to high water content regions in solvents.

Bathochromic or hypsochromic shift-type mechanofluorochromism (b-MFC or h-MFC) was found for (D-pi-)(2)A-type azine-based fluorescent dyes OUY-2, OUK-2, and OUJ-2 possessing intramolecular charge-transfer (ICT) characteristics from two (diphenylamino)carbazole-thiophene units as D (electron-donating group)-pi (pi-conjugated bridge) moieties to a pyridine, pyrazine, or triazine ring as A (electron-withdrawing group): grinding of the recrystallized dyes induced red or blue shifts of the fluorescent colors, that is, bathochromic or hypsochromic shifts of the fluorescence maximum wavelengths (lambda(fl-solid)(max)). The degrees of MFC evaluated by the absolute value of differences (Delta lambda(fl-solid)(max)) in lambda(fl-solid)(max) before and after grinding of the recrystallized dyes increased in the order of OUY-2 (+7 nm) < OUK-2 (-17 nm) < OUJ-2 (+45 nm), so that OUJ-2 exhibits obvious b-MFC, but OUK-2 exhibits h-MFC. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) demonstrated that the recrystallized dyes were in the crystalline state but the ground dyes were in the amorphous state. When the ground solids were heated above their crystallization temperatures (T-c), the colors and fluorescent colors recovered to the original ones before grinding or converted to other ones, that is, heating the ground solids in the amorphous state induced the recrystallization to recover the original microcrystals or to form other microcrystals due to polymorph transformation. However, (D-pi-)(2)Ph-type fluorescent dye OTK-2 having a phenyl group as a substitute for the azine rings exhibited non-obvious MFC. Molecular orbital (MO) calculations indicated that the values of the dipole moments (mu(g)) in the ground state were 4.0 debye, 1.4 debye, 3.2 debye, and 2.9 debye for OTK-2, OUY-2, OUK-2, and OUJ-2, respectively. Consequently, on the basis of experimental results and MO calculations, we have demonstrated that the MFC of the (D-pi-)(2)A-type azine-based fluorescent dyes is attributed to reversible switching between the crystalline state of the recrystallized dyes and the amorphous state of the ground dyes with changes in the intermolecular dipole-dipole and pi-pi interactions before and after grinding. Moreover, this work reveals that (D-pi-)(2)A fluorescent dyes possessing dipole moments of ca. 3 debye as well as moderate or intense ICT characteristics make it possible to activate the MFC.

Anthracene-(aminomethyl)phenylboronic acid pinacol ester (AminoMePhenylBPin) SM-1 having a cyano group as an electron-withdrawing substituent and a hydroxymethyl group has been developed as a highly sensitive PET (photo-induced electron transfer)-type fluorescent sensor for visualization, detection, and quantification of trace amounts of water. SM-1 shows enhancement of fluorescence with the increase in water content in various solvents (polar, less polar, protic, and aprotic solvents), which is attributed to the suppression of PET due to the formation of the PET inactive (fluorescent) species SM-1a by interaction with water molecules. In fact, the formation of SM-1a by interaction with water molecules has been successfully detected by H-1 NMR spectral measurements. The detection limits (DLs) and quantitation limits (QLs) of SM-1 for water in solvents are, respectively, 0.006 and 0.018 wt% in 1,4-dioxane, 0.004 and 0.012 wt% in THF, 0.004 and 0.013 wt% in acetonitrile, and 0.007 and 0.021 wt% in ethanol, which are superior to those of OF-2 without a hydroxymethyl group. This result is attributed to the improvement of fluorescence emission properties by the introduction of a hydroxymethyl group to an anthracene fluorophore. Actually, fluorescence quantum yields (phi(fl)) of OF-2 and SM-1 in absolute acetonitrile are below 2%, but in acetonitrile with 1 wt% water content the phi(fl) of SM-1 (20%) is higher than that of OF-2 (13%). Moreover, we have achieved the preparation of various types of polymer films (polystyrene (PS), poly(4-vinylphenol) (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG)) doped with SM-1, and investigated the optical sensing properties of the SM-1-doped polymer films for water. It was found that the SM-1-doped polymer films produce a reversible switching in fluorescence color between the green excimer emission in the PET active state under a drying process and the blue monomer emission in the PET inactive state upon exposure to moisture. Herein, we propose that PET-type fluorescent sensor-doped polymer films based on a fluorescence enhancement system are one of the most promising and convenient functional materials for not only environmental and quality control monitoring systems and industry, but also visualizing the droplet on material surfaces.

Benzofuro[2,3-c]carbazoloquinol derivatives, a new type of fluorescent dyes, were derived from the corresponding quinone, and their optical and electrochemical properties were investigated by photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculation. The quinol derivatives in 1,4-dioxane showed the photoabsorption band at around 435 nm (molar extinction coefficient (epsilon(max)) = ca. 6000-8000 M-1 cm(-1)) and the fluorescence band at around 520 nm (fluorescence quantum yield (Phi(fl)) = 0.24-0.28). The CV demonstrated that the quinol derivatives exhibit an irreversible oxidation wave at around -0.28 V versus Fc/Fc(+). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the quinol derivatives which were calculated using DFT at the B3LYP/6-31G(d,p) level are in good agreement with the experimental results. (C) The Author(s) 2021. Published by ECSJ.

4,4'-Bibenzo[c]thiophene fluorophores (1,1'-Si-4,4'-BBT, 1,1'-Sn-4,4'-BBT, 1,1'-CHO-4,4'-BBT and 1,1'-PhtBu-4,4'-BBT) with various substituents (-Si(CH3)(2)C(CH3)(3), -Sn(CH3)(3), -CHO and -PhtBu) at the 1,1'-positions on the thiophene rings have been developed. The photoabsorption and fluorescence maxima (lambda(abs)(max) and lambda(fl)(max)) of the 1,1'-disubstituted 4,4'-bibenzo[c]thiophene derivatives in toluene exhibit bathochromic shifts in the order of 1,1'-Si-4,4'-BBT (366 and 420 nm) approximate to 1,1'-Sn-4,4'-BBT (367 and 422 nm) < 1,1'-PhtBu-4,4'-BBT (386 and 469 nm) <= 1,1'-CHO-4,4'-BBT (395 and 456 nm), compared to those (359 and 410 nm) of the unsubstituted 4,4'-bibenzo[c]thiophene (4,4'-BBT). The fluorescence quantum yields (phi(fl)) of the 1,1'-disubstituted 4,4'-bibenzo[c]thiophene derivatives except 1,1'-CHO-4,4'-BBT (phi(fl) = 0.03) are ca. 0.4 in toluene. The HOMO energy levels rise in the order of 4,4'-BBT (-5.55 eV) < 1,1'-Si-4,4'-BBT (-5.45 eV) approximate to 1,1'-Sn-4,4'-BBT (-5.43 eV) < 1,1'-PhtBu-4,4'-BBT (-5.22 eV), but the LUMO energy levels (ca. -2.35 eV) of the four derivatives are similar to each other, leading to the bathochromic shift of the photoabsorption band from 4,4'-BBT to 1,1'-PhtBu-4,4'-BBT. On the other hand, the HOMO and LUMO energy levels (-5.79 eV and -2.90 eV) of 1,1'-CHO-4,4'-BBT are significantly lower than those of 4,4'-BBT, but the lowering in the LUMO energy level is larger than that in the HOMO energy level, resulting in the bathochromic shift of the photoabsorption. It is worth mentioning that in the solid state, 1,1'-Si-4,4'-BBT and 1,1'-Sn-4,4'-BBT show relatively high phi(fl-solid) values of 0.22 and 0.40, respectively, whereas 4,4'-BBT, 1,1'-CHO-4,4'-BBT and 1,1'-PhtBu-4,4'-BBT exhibit feeble solid-state fluorescence properties (phi(fl-solid) <= 0.04). This work provides the synthetic strategy for 1,1'-disubstituted 4,4'-bibenzo[c]thiophene derivatives and reveals their optical properties in the solution and the solid state and electrochemical properties.

Previously, we developed a simple method to fabricate a composite film of a conducting polymer (PEDOT:PSS) and single-walled carbon nanotubes (SWCNTs) that exhibited high thermoelectric performance. In the present work, the carrier density of the composite film was controlled using an electrochemical method. The thermoelectric performances of the obtained composite films were analyzed in terms of their carrier densities. The electrical conductivities of the composite films were affected by the change in the carrier species of PEDOT:PSS, but overall the values were relatively high owing to the SWCNTs. The Seebeck effect showed a unique behavior reflecting the van Hove singularity in response to variations in the carrier density.

Phenazine-2,3-diol derivatives KO-0-3, which have zero to three formyl groups, respectively, have been developed as photosensitizers (PSs) possessing the ability to generate singlet oxygen (O-1(2)). The photoabsorption bands of KO-0-3 are significantly red-shifted compared to those of phenazine-2,3-MOM (methoxymethyl) derivatives 5-8, whose hydroxy and formyl groups are protected, and have onsets at around 600-650 nm. Furthermore, the fluorescence quantum yields (phi(fl)) of KO-0-3 (phi(fl) = 0.024-0.097) are lower than those of 5-8 (phi(fl) = 0.34-0.46) in solution. To gain insight into the O-1(2) generation properties of KO-0-3, we evaluated the O-1(2) quantum yields (phi(Delta)) and rate constants (k(obs)), and demonstrated that KO-1-3 possess a higher ability to generate O-1(2) under visible light irradiation than those of 5-8. Moreover, it was found that the phi(Delta) values of KO-0-3 increase in the order of KO-0 (0.036) < KO-1 (0.22) < KO-2 (0.33) < KO-3 (0.41) with increasing number of formyl groups. This result indicates that formyl groups facilitate the intersystem crossing (ISC) from the lowest singlet excited states of the PSs (S-1) to the triplet excited states (T-n) according to El-Sayed's rule. Consequently, this work provides useful knowledge in molecular design of efficient phenazine-2,3-diol-based PSs for photodynamic therapy (PDT).

<p>4,4′-Bibenzo[<italic>c</italic>]thiophene <bold>4,4′-BBT</bold> and its silyl-substituted derivatives <bold>1,1′-Si-4,4′-BBT</bold> and <bold>1,1′,3,3′-Si-4,4′-BBT</bold> have been designed and developed as new π-building blocks.</p>

Anthracene-(aminomethyl)phenylboronic acid pinacol ester (AminoMePhenylBPin) OF-2 acts as a PET (photo-induced electron transfer)-type fluorescent sensor for determination of a trace amount of water: the addition of water to organic solvents containing OF-2 causes a drastic and linear enhancement of fluorescence emission as a function of water content, which is attributed to the suppression of PET. Indeed, detection limits (DLs) for OF-2 were as low as 0.01-0.008 wt% of water in solvents, that is, the PET method makes it possible to visualize, detect, and determine a trace amount of water. Thus, in this work, in order to develop fluorescent polymeric materials for visualization and detection of water, we have achieved the preparation of various types of polymer films (polystyrene (PS), poly(4-vinylphenol) (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG)) which were doped with OF-2, and investigated the optical sensing properties of the OF-2-doped polymer films for water. As-prepared OF-2-doped polymer films initially exhibited green excimer emission in the PET active state, but blue monomer emission in the PET inactive state upon exposure to moisture or by water droplet. Moreover, it was found that the OF-2-doped polymer films show the reversible fluorescence properties in the dry-wet process. Herein we propose that polymer films doped with PET-type fluorescent sensors for water based on a fluorescence enhancement (turn-on) system are one of the most promising and convenient functional materials for visualizing moisture and water droplets.

We have designed and synthesized an SFC (solvatofluorochromism)/AIEE (aggregation-induced emission enhancement)-based fluorescence sensorTPE-(An-CHO) composed of an electron-donating tetraphenylethene (TPE) core and four electron-accepting anthraldehydes as peripheral units.TPE-(An-CHO) possesses both solvatofluorochromic properties and AIEE characteristics for detection of water over a wide range from low water content to high water content region in organic solvents.TPE-(An-CHO) showed a feeble fluorescence band at around 500 nm originating from the anthraldehyde units in absolute THF. The addition of water to the THF solution containingTPE-(An-CHO) caused red-shifts of the fluorescence band and changes in the fluorescence intensity. In the low water content region below 30 wt%,TPE-(An-CHO) exhibited a linear increase in the fluorescence intensity with a red-shift of the fluorescence band with the increase in the water content, that is, the positive solvatofluorochromic properties based on the intramolecular charge transfer (ICT) characteristics due to increasing the solvent polarity. A broad fluorescence band at around 540 nm originating from the AIEE characteristics due to the restricted intramolecular rotation (RIR) of the TPE core associated with the aggregate formation was enhanced and dominated the fluorescence spectra from the relatively low water content of 40 wt%. Indeed, the plots against the water fraction in the THF solutions forTPE-(An-CHO) indicated that the fluorescence intensity gradually and almost linearly increased with the increase in the water content over a wide range from 0 wt% to 90 wt%. In contrast,TPE-(An-CHO)composed of a TPE and an anthraldehyde unit exhibited AIEE characteristics in the high water content region over 80 wt%, although in the low water content region below 20 wt%,TPE-(An-CHO)showed positive solvatofluorochromic properties. The AIEE characteristics ofTPE-(An-CHO) observed in the low water content region are attributed to the fact that the four anthraldehyde units lowered the solubility in organic solvents and water. This work reveals the solvatofluorochromic properties and the AIEE characteristics of donor-acceptor-type TPE-anthracene-based fluorescence sensors for water. 4 4 4 4 4 4 4

A postpolymerization nucleophilic aromatic substitution reaction is used as a strategy to efficiently diversify conjugated polymers. Conjugated polymers and small molecular models bearing tetrafluorophenyl and octafluorobiphenyl units are reacted with thiophenol derivatives, phenol derivatives, and carbazole in the presence of bases. Model reactions provide insights into the reactivity, numbers and patterns of substitution, structural features, and spectroscopic data. Thiophenol derivatives and carbazole achieve complete substitution of fluorine atoms in both the polymer and the model reactions, whereas phenol derivatives result in disubstitution in each arene ring with para-selectivity. The highly twisted and structurally rigid main chain structures are confirmed for a fully substituted arene motif in both the polymers and the models, resulting in the formation of syn- and anti-atropisomer or axial chirality and in the twisted intramolecular charge transfer character. The obtained polymers and models show unique optical and electrochemical properties, including phosphorescence at low temperatures in the case of the sulfur-containing materials.

A postpolymerization nucleophilic aromatic substitution reaction is used as a strategy to efficiently diversify conjugated polymers. Conjugated polymers and small molecular models bearing tetrafluorophenyl and octafluorobiphenyl units are reacted with thiophenol derivatives, phenol derivatives, and carbazole in the presence of bases. Model reactions provide insights into the reactivity, numbers and patterns of substitution, structural features, and spectroscopic data. Thiophenol derivatives and carbazole achieve complete substitution of fluorine atoms in both the polymer and the model reactions, whereas phenol derivatives result in di-substitution in each arene ring with para-selectivity. The highly twisted and structurally rigid main chain structures are confirmed for a fully substituted arene motif in both the polymers and the models, resulting in the formation of syn- and anti-atropisomer or axial chirality and in the twisted intramolecular charge transfer character. The obtained polymers and models show unique optical and electrochemical properties, including phosphorescence at low temperatures in the case of the sulfur-containing materials.

We have designed and synthesized an SFC (solvatofluorochromism)/AIEE (aggregation-induced emission enhancement)-based fluorescence sensor TPE-(An-CHO)4 composed of an electron-donating tetraphenylethene (TPE) core and four electron-accepting anthraldehydes as peripheral units. TPE-(An-CHO)4 possesses both solvatofluorochromic properties and AIEE characteristics for detection of water over a wide range from low water content to high water content region in organic solvents. TPE-(An-CHO)4 showed a feeble fluorescence band at around 500 nm originating from the anthraldehyde units in absolute THF. The addition of water to the THF solution containing TPE-(An-CHO)4 caused red-shifts of the fluorescence band and changes in the fluorescence intensity. In the low water content region below 30 wt%, TPE-(An-CHO)4 exhibited a linear increase in the fluorescence intensity with a red-shift of the fluorescence band with the increase in the water content, that is, the positive solvatofluorochromic properties based on the intramolecular charge transfer (ICT) characteristics due to increasing the solvent polarity. A broad fluorescence band at around 540 nm originating from the AIEE characteristics due to the restricted intramolecular rotation (RIR) of the TPE core associated with the aggregate formation was enhanced and dominated the fluorescence spectra from the relatively low water content of 40 wt%. Indeed, the plots against the water fraction in the THF solutions for TPE-(An-CHO)4 indicated that the fluorescence intensity gradually and almost linearly increased with the increase in the water content over a wide range from 0 wt% to 90 wt%. In contrast, TPE-(An-CHO) composed of a TPE and an anthraldehyde unit exhibited AIEE characteristics in the high water content region over 80 wt%, although in the low water content region below 20 wt%, TPE-(An-CHO) showed positive solvatofluorochromic properties. The AIEE characteristics of TPE-(An-CHO)4 observed in the low water content region are attributed to the fact that the four anthraldehyde units lowered the solubility in organic solvents and water. This work reveals the solvatofluorochromic properties and the AIEE characteristics of donor–acceptor-type TPE–anthracene-based fluorescence sensors for water.

Anthracene-(aminomethyl)phenylboronic acid pinacol ester (AminoMePhenylBPin) OF-2 acts as a PET (photo-induced electron transfer)-type fluorescent sensor for determination of a trace amount of water: the addition of water to organic solvents containing OF-2 causes a drastic and linear enhancement of fluorescence emission as a function of water content, which is attributed to the suppression of PET. Indeed, detection limits (DLs) for OF-2 were as low as 0.01–0.008 wt% of water in solvents, that is, the PET method makes it possible to visualize, detect, and determine a trace amount of water. Thus, in this work, in order to develop fluorescent polymeric materials for visualization and detection of water, we have achieved the preparation of various types of polymer films (polystyrene (PS), poly(4-vinylphenol) (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG)) which were doped with OF-2, and investigated the optical sensing properties of the OF-2-doped polymer films for water. As-prepared OF-2-doped polymer films initially exhibited green excimer emission in the PET active state, but blue monomer emission in the PET inactive state upon exposure to moisture or by water droplet. Moreover, it was found that the OF-2-doped polymer films show the reversible fluorescence properties in the dry–wet process. Herein we propose that polymer films doped with PET-type fluorescent sensors for water based on a fluorescence enhancement (turn-on) system are one of the most promising and convenient functional materials for visualizing moisture and water droplets.

We designed and synthesized unsubstituted 4,4′-bibenzo[c]thiophene 4,4′-BBT and its silyl-substituted derivatives 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT with one or two tert-butyldimethylsilyl groups on each thiophene ring, as new π-building blocks in emitters, photosensitizers and semiconductors for organic optoelectronic devices. The characterization of 4,4′-BBT, 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT was successfully determined by FTIR, 1H and 13C NMR measurements, high-resolution mass spectrometry (HRMS) analysis, photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculations. Moreover, a single-crystal X-ray structural analysis was successfully made for 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT. The photoabsorption and fluorescence maxima (λabsmax and λflmax) of the three 4,4′-bibenzo[c]thiophene derivatives in toluene exhibit bathochromic shifts in the order of 4,4′-BBT (359 nm and 410 nm) < 1,1′-Si-4,4′-BBT (366 nm and 420 nm) < 1,1′,3,3′-Si-4,4′-BBT (371 nm and 451 nm). The HOMO and LUMO energy levels rise in the order of 4,4′-BBT (−5.55 eV and −2.39 eV) < 1,1′-Si-4,4′-BBT (−5.45 eV and −2.34 eV) < 1,1′,3,3′-Si-4,4′-BBT (−5.34 eV and −2.30 eV), but the rise of the HOMO energy level is larger than that of the LUMO energy level, resulting in the bathochromic shift of the photoabsorption band from 4,4′-BBT to 1,1′,3,3′-Si-4,4′-BBT. The fluorescence quantum yields (Φfl) of 4,4′-BBT, 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT in toluene are 0.41, 0.41 and 0.36, respectively. It is worth mentioning that in the solid state 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT show relatively high Φfl-solid values of 0.22 and 0.25, respectively, whereas 4,4′-BBT exhibits poor solid-state fluorescence properties (Φfl-solid < 0.02). This work provides an efficient synthetic method for the 4,4′-bibenzo[c]thiophene derivatives and their photophysical properties in the solution and solid state, electrochemical properties and X-ray crystal structures.

One promising application of self-healing polymeric materials is biomedical use. Although charge-transfer (CT) interactions have been employed to construct self-healing polymers as well as other reversible bonds and interactions, their potential for biomedical applications has never been investigated. In this study, we fabricated self-healable and cell-compatible polyurethane elastomers cross-linked by CT complexes between electron-rich pyrene (Py) and electron-deficient naphthalene diimide (NDI) by simply blending two linear polymers with Py or NDI as a repeating unit. The elastomers with different blend ratios self-healed damage over 1 day in mild conditions, including in air and water at 30–100 °C. The mechanical properties of damaged elastomers were almost restored after healing in air at 100 °C, and even in air at 30 °C and in water at 70 °C, healing was also possible to a certain extent. The good cell compatibility of the polyurethane elastomers was demonstrated by culturing two kinds of cells on the thin film substrates.

A propeller-structured 3,5,8-trithienyl-BODIPY-type pyridine-boron trifluoride complex,ST-3-BF3, which has three units of 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, was designed and developed as an intramolecular charge transfer (ICT)-type optical sensor for the detection of a trace amount of water in acetonitrile. The characterization ofST-3-BF(3)was successfully determined by FTIR,H-1 and(11)B NMR measurements, high-resolution mass spectrometry (HRMS) analysis, thermogravimetry-differential thermal analysis (TG-DTA), photoabsorption and fluorescence spectral measurements, and density functional theory (DFT) calculations.ST-3-BF(3)showed a broad photoabsorption band in the range of 600 to 800 nm, which is assigned to the S-0 -> S(1)transition of the BODIPY skeleton with the expanded pi-conjugated system over the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at the 3-, 5-, and 8-positions onto the BODIPY core. In addition, a photoabsorption band was also observed in the range of 300 to 550 nm, which can be assigned to the ICT band between the 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile units at 3-, 5-, and 8-positions and the BODIPY core.ST-3-BF(3)exhibited a characteristic fluorescence band originating from the BODIPY skeleton at around 730 nm. It was found that by addition of a trace amount of water to the acetonitrile solution ofST-3-BF3, the photoabsorption band at around 415 nm and the fluorescence band at around 730 nm increased linearly as a function of the water content below only 0.2 wt%, which could be ascribed to the change in the ICT characteristics due to the dissociation ofST-3-BF(3)intoST-3by water molecules. Thus, this work demonstrated that the 3,5,8-trithienyl-BODIPY-type pyridine-boron trifluoride complex can act as a highly-sensitive optical sensor for the detection of a trace amount of water in acetonitrile.

We designed and developed propeller-type 3,5,8-trithienyl-BODIPY dyesST-1,ST-2, andST-3, which have the same three units of tetramethyl-2-(thiophen-2-yl)-1,3-dioxolane, thiophene-2-carbaldehyde, or 2-(pyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile at the 3-, 5-, and 8-positions on the BODIPY skeleton, respectively. In order to get an insight into the impacts of 3,5,8-trithienyl substituents on the BODIPY core on the optical and electrochemical properties, we performed the photoabsorption and fluorescence spectroscopy, Lippert-Mataga plots, cyclic voltammetry (CV) and density functional theory (DFT) calculations forST-1,ST-2, andST-3. The photoabsorption and fluorescence maxima (lambda absmax and lambda flmax) of the three 3,5,8-trithienyl-DODIPY dyes exhibit bathochromic shifts in the order ofST-1(ca.640 and 660 nm) <ST-2(ca.660 and 680 nm) <ST-3(ca.730 and 750 nm), which appear in significantly longer wavelength regions compared to those of the 3,5,8-triphenyl BODIPY dye. This fact indicates that the expansion of the pi-conjugated system by the introduction of thiophene units as spacers at the 3-, 5-, and 8-positions onto the BODIPY core can lead to bathochromic shifts of photoabsorption and fluorescence bands to the red/NIR region. It was found that the photoabsorption and fluorescence bands of the propeller-type 3,5,8-trithienyl-BODIPY dyes are nearly independent of solvent polarity, that is,ST-1,ST-2, andST-3show feeble solvatochromic properties. Moreover, we revealed thatST-3possesses the ability to generate singlet oxygen (O-1(2)) under visible light irradiation, and thus, this result provides useful knowledge in molecular design of efficient BODIPY-based photosensitizers for photodynamic therapy (PDT).

Fluorescent sensors DJ-1 and DJ-2 with a large Stokes shift (SS) based on a combination of PET (photoinduced electron transfer) and FRET (Forster resonance energy transfer) have been developed for the detection of water in organic solvents. DJ-1 is composed of anthracene-(aminomethyl)phenylboronic acid ester as the PET-type donor fluorophore and a BODIPY skeleton as the acceptor fluorophore in the FRET process. In contrast, DJ-2 is composed of an anthracene skeleton as the donor fluorophore and a BODIPY-(aminomethyl)phenylboronic acid ester skeleton as the PET-type acceptor fluorophore in the FRET process. In fact, the addition of water to organic solvents containing DJ-1 or DJ-2 caused both PET suppression and energy transfer from the donor fluorophore to the acceptor fluorophore through the FRET process, thus resulting in an enhancement of the fluorescence band originating from the BODIPY skeleton. In addition, the pseudo-SS values of DJ-1 and DJ-2 between the photoabsorption maximum of the anthracene fluorophore and the fluorescence maximum of the BODIPY fluorophore are 7563 cm(-1) (141 nm) and 8017 cm(-1) (153 nm), respectively, which are significantly higher than those of a typical PET-based fluorescent sensor. It was found that the FRET efficiency for DJ-1 is quantitative, but that for DJ-2 was estimated to be ca. 50% based on time-resolved fluorescence lifetime measurements. Moreover, the detection limit of DJ-1 for water is superior to that of DJ-2. Based on the fluorescence sensing mechanism of DJ-1 and DJ-2 for water, we propose that a combination of a PETtype donor fluorophore and an acceptor fluorophore in the FRET process is one of the most promising molecular designs to create an efficient fluorescent sensor for the detection of water in organic solvents.

An optical sensor with the ability to detect and determine water over a wide concentration range is highly desirable in the laboratory and industry. Here the sensitivity and spectral responses of an intramolecular charge transfer-type colorimetric and fluorescence sensor with beta-carboline structure are tuned and improved significantly over various water contents in the organic solvent by fusion with an electron-donating juloidine structure and complexation with boron trifluoride (BF3). The sensors, ET-1 and ET-1-BF3, developed in this study can respond differently depending on water content. ET-1-BF3 releases BF3 to generate ET-1 by addition of a trace amount of water, and ET-1 forms hydrogen bonds with one water molecule in low water contents and a hydrogen-bonded proton transfer complex with several water molecules in high water contents, accompanying gradual color and fluorescence changes. This work shows a promising approach to the sensitive detection and precise determination of water over the whole concentration range using a simple and practical method with optical sensors.

The donor-acceptor-pi-conjugated (D-pi-)(2)A fluorescent dyes OUY-2, OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)-pi (pi-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert-Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (lambda(max,abs)) and the fluorescence maximum (lambda(max,fl)) for the intramolecular charge-transfer characteristic band of the (D-pi-)(2)A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2. Moreover, the photoabsorption bands of the (D-pi-)(2)A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert-Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Delta mu (= mu(e) - mu(g)) value, which is the difference in the dipole moment of the dye between the excited (mu(e)) and the ground (mu(g)) states, increases in the order of OUY-2 < OUK-2 < OUJ-2. Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in non-polar solvents. The cyclic voltammetry of OUY-2, OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK-2 > OUJ-2. Consequently, this work reveals that for the (D-pi-)(2)A fluorescent dyes OUY-2, OUK-2 and OUJ-2 the bathochromic shifts of lambda(max,abs) and lambda(max,fl) and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2.

An anthracene-(aminomethyl)phenylboronic acid ester-BODIPY (DJ-1) was designed and developed as a fluorescent sensor based on photo-induced electron transfer (PET) and Forster resonance energy transfer (FRET) for the detection of a trace amount of water in solvents, where the anthracene skeleton and BODIPY skeleton are the donor fluorophore and the acceptor fluorophore in the FRET process, respectively. It was found that the addition of water to organic solvents containing DJ-1 causes both the suppression of PET in the anthracene-(aminomethyl)phenylboronic acid ester as the PET-type fluorescent sensor skeleton and the energy transfer from the anthracene skeleton to the BODIPY skeleton through a FRET process, thus resulting in the enhancement of the fluorescence band originating from the BODIPY skeleton. This work demonstrates that the PET/FRET-based fluorescent dye composed of the donor fluorophore possessing PET characteristics and the acceptor fluorophore in the FRET process can act as a fluorescent sensor with a large SS for the detection of a trace amount of water in solvents.

Herein, we report the fabrication of photoresponsive three-dimensional (3D) fiber scaffolds for the first time, where photoresponsive polymers are localized on their fiber surfaces of nano thickness, using a simple and practical co-axial (core-sheath) electrospinning technique. Cell adhesion to the 3D scaffolds was regulated by photostimulation.

Photoregulation of polymer chain scission based on a Diels-Alder (DA) adduct containing diarylethene (DAE) was investigated. Poly(epsilon-caprolactone) with a DA adduct conjugated with DAE skeleton (DAE/DA) at the center of the chain was synthesized by ring-opening living cationic polymerization of epsilon-caprolactone, initiating from diol-type DAE/DA, and its chain scission via thermally induced retro-DA reaction was successfully controlled by photoisomerization of DAE.

Photoregulation of polymer chain scission based on a Diels-Alder (DA) adduct containing diarylethene (DAE) was investigated. Poly(epsilon-caprolactone) with a DA adduct conjugated with DAE skeleton (DAE/DA) at the center of the chain was synthesized by ring-opening living cationic polymerization of epsilon-caprolactone, initiating from diol-type DAE/DA, and its chain scission via thermally induced retro-DA reaction was successfully controlled by photoisomerization of DAE.

The surface of cellulose nanocrystals (CNCs) was modified with a scissile but reversibly recombinable dynamic covalent mechanophore, and the activation of the mechanophore on the CNC surface in bulk was investigated. The recombination behaviour of the activated surface-modified mechanophore exhibited high sensitivity to mechanical stress because of the limited molecular mobility. The modified CNCs could be used to effectively reinforce a self-healable polymer containing similar dynamic covalent linkages through the formation of reversible covalent bonds between the CNC surfaces and the polymer matrix, while the nanocomposite retained the ability to heal. The results of the present study appear to be broadly useful for designing composite materials with fascinating functional properties such as damage self-reporting and self-healing.

Mechanoresponsive polymers can have attractive functions; however, the relationship between polymer architecture and mechanoresponsiveness in the bulk state is still poorly understood. Here, we designed well-defined linear and star polymers with a mechanophore at the center of each architecture, and investigated the effect of molecular weight and branched structures on mechanoresponsiveness in the solid state. Diarylbibenzofuranone, which can undergo homolytic cleavage of the central C-C bond by mechanical force to form blue-colored radicals, was used as a mechanophore because the cleaved radicals could be evaluated quantitatively using electron paramagnetic resonance measurements. We confirmed that longer polymer chains induce mechanochemical activation more effectively and found that, in the bulk state, the star polymers have higher sensitivity to mechanical stress compared with a linear polymer having similar molecular weight arm segment.

Polymer inorganic composites with diaryl-bibenzofuranone (DABBF) moieties, dynamic covalent mechanochromophores, were prepared, and their mechanochromic behavior was systematically investigated. The central C-C bonds in DABBF moieties can be cleaved by mechanical force to form the corresponding stable blue radicals, which can be quantitatively evaluated by electron paramagnetic resonance (EPR) spectroscopy. One controversial issue but attractive property in the DABBF system is the equilibrium between the activated and deactivated states. Although the deactivation process decreases the sensitivity of some equilibrium mechanophores, the equilibrium has rarely been considered when establishing molecular and/or material design of these systems. Herein, a rational macromolecular design to suppress the deactivation of activated dynamic mechanophores and improve sensitivity by limiting their molecular motion is proposed. Polymer-inorganic composite materials with rigid networks prepared from DABBF alkoxysilane derivatives exhibited significant activation of the incorporated DABBF linkages by grinding, with sensitivities more than 50 times as high as that of DABBF monomers. The increased sensitivity is due to the effective transmission of mechanical force to the DABBF moieties in the network structures and suppression of the recombination of the generated radicals by the rigid frameworks. Furthermore, when the rigid frameworks were incorporated into elastomers as inorganic hard domains, the DABBF mechanophores at the interface between the organic and inorganic domains were preferentially activated by elongation.

Autonomously substitutable organosilane thin films based on diarylbibenzofuranone (DABBF) units were prepared, and the radical exchange reactions of the DABBF units at the surface resulted in chemically reversible surface character changes without external stimuli. The reversible changes of the surface properties were confirmed by X-ray photoelectron spectroscopy and water contact angle measurements.

Polymer inorganic composites with diaryl-bibenzofuranone (DABBF) moieties, dynamic covalent mechanochromophores, were prepared, and their mechanochromic behavior was systematically investigated. The central C-C bonds in DABBF moieties can be cleaved by mechanical force to form the corresponding stable blue radicals, which can be quantitatively evaluated by electron paramagnetic resonance (EPR) spectroscopy. One controversial issue but attractive property in the DABBF system is the equilibrium between the activated and deactivated states. Although the deactivation process decreases the sensitivity of some equilibrium mechanophores, the equilibrium has rarely been considered when establishing molecular and/or material design of these systems. Herein, a rational macromolecular design to suppress the deactivation of activated dynamic mechanophores and improve sensitivity by limiting their molecular motion is proposed. Polymer-inorganic composite materials with rigid networks prepared from DABBF alkoxysilane derivatives exhibited significant activation of the incorporated DABBF linkages by grinding, with sensitivities more than 50 times as high as that of DABBF monomers. The increased sensitivity is due to the effective transmission of mechanical force to the DABBF moieties in the network structures and suppression of the recombination of the generated radicals by the rigid frameworks. Furthermore, when the rigid frameworks were incorporated into elastomers as inorganic hard domains, the DABBF mechanophores at the interface between the organic and inorganic domains were preferentially activated by elongation.

Autonomously substitutable organosilane thin films based on diarylbibenzofuranone (DABBF) units were prepared, and the radical exchange reactions of the DABBF units at the surface resulted in chemically reversible surface character changes without external stimuli. The reversible changes of the surface properties were confirmed by X-ray photoelectron spectroscopy and water contact angle measurements.

Repeated mechanical scission and recombination of dynamic covalent bonds incorporated in segmented polyurethane elastomers are demonstrated by utilizing a diarylbibenzofuranone-based mechanophore and by the design of the segmented polymer structures. The repeated mechanochemical reactions can accompany clear colouration and simultaneous fading.

Mechanoresponsive polymers can have attractive functions; however, the relationship between polymer architecture and mechanoresponsiveness in the bulk state is still poorly understood. Here, we designed well-defined linear and star polymers with a mechanophore at the center of each architecture, and investigated the effect of molecular weight and branched structures on mechanoresponsiveness in the solid state. Diarylbibenzofuranone, which can undergo homolytic cleavage of the central C-C bond by mechanical force to form blue-colored radicals, was used as a mechanophore because the cleaved radicals could be evaluated quantitatively using electron paramagnetic resonance measurements. We confirmed that longer polymer chains induce mechanochemical activation more effectively and found that, in the bulk state, the star polymers have higher sensitivity to mechanical stress compared with a linear polymer having similar molecular weight arm segment.

Controlled scrambling reactions of polybutadiene and olefin-containing polyurethane prepared by step-growth or chain-growth polymerization were accomplished via macromolecular olefin cross-metathesis in the presence of Grubbs' second-generation catalyst to yield scrambled copolymers with different thermal and mechanical properties. In addition, naturally occurring polyisoprene and olefin-containing polyurethane were successfully scrambled, demonstrating that these polymers can be used to synthesize natural/synthetic hybrid materials by the cross-metathesis reaction. Effects of reaction time, solvent, and homopolymer structure on these scrambling reactions were investigated. This metathesis-based approach facilitates the precise control of the scrambling reactions under the applied reaction conditions, thus affording the desired polymer structures with compositions ranging from multiblock to random compositions and enhanced mechanical properties. (C) 2015 Elsevier Ltd. All rights reserved.

Stress evaluation in polymeric materials is important in order to not only spot danger in them before serious failure, but also precisely interpret the destructive mechanism, which can improve the lifetime and durability of polymeric materials. Here, we are able to visualize stress by color changes, as well as quantitatively estimate the stress in situ, in segmented polyurethane elastomers with diarylbibenzofuranone-based dynamic covalent mechanophores. We prepared films of the segmented polyurethanes, in which the mechanophores were incorporated in the soft segments, and efficiently activated them by mechanical force. Cleavage of the mechanophores during uniaxial elongation and their recovery after the removal of the stress were quantitatively evaluated by in situ electron paramagnetic resonance measurements, accompanied by drastic color changes.

A lot of self-healing materials using dynamic bonding systems have been reported, while the focus is mainly on the macroscopic self-healing behavior such as visually recognizable healing. Because the healing originates from microscopic chemical reactions of the dynamic bonds, evaluation of the reactions in the materials is necessary for elucidation of the healing mechanisms and development of the healing ability. Herein, we demonstrated self-healing of a cross-linked polymer with diarylbibenzofuranone (DABBF)-based dynamic covalent linkages at mild temperature and investigated the healing behavior from both macroscopic and microscopic viewpoints. The macroscopic behavior was inspected by mechanical tests, and the linkage reaction (equilibrium) was evaluated by electron paramagnetic resonance measurements. These assessments revealed that the healing is strongly dependent on temperature, which is attributable to synergism between changes in the chain mobility and in the equilibrium of the incorporated linkages. These findings would be applicable to other dynamic bonding systems.

Visualization and quantitative evaluation of covalent bond scission in polymeric materials are highly important for understanding failure, fatigue, and deterioration mechanisms and improving the lifetime, durability, toughness, and reliability of the materials. The diarylbibenzofuranone-based mechanophore radical system enabled, through electron paramagnetic resonance spectroscopy, insitu quantitative evaluation of scission of the mechanophores and estimation of mechanical energy induced along polymer chains by external forces. The coagulation of polymer solutions by freezing probably generated force but did not cleave the mechanophores. On the other hand, cross-linking led to efficient propagation of the force of more than 80kJmol(-1) to some mechanophores, resulting their cleavage and generation of colored stable radicals. This mechanoprobe concept has the potential to elucidate other debated issues in the polymer field as well.

Controlled scrambling reactions of polybutadiene and olefin-containing polyurethane prepared by step-growth or chain-growth polymerization were accomplished via macromolecular olefin cross-metathesis in the presence of Grubbs' second-generation catalyst to yield scrambled copolymers with different thermal and mechanical properties. In addition, naturally occurring polyisoprene and olefin-containing polyurethane were successfully scrambled, demonstrating that these polymers can be used to synthesize natural/synthetic hybrid materials by the cross-metathesis reaction. Effects of reaction time, solvent, and homopolymer structure on these scrambling reactions were investigated. This metathesis-based approach facilitates the precise control of the scrambling reactions under the applied reaction conditions, thus affording the desired polymer structures with compositions ranging from multiblock to random compositions and enhanced mechanical properties. (C) 2015 Elsevier Ltd. All rights reserved.

Plasticizer-promoted thermal crosslinking reactions of an alkoxyamine-appended poly(methyl methacrylate)-based dynamic covalent polymer were successfully performed under bulk conditions. The films of the dynamic covalent polymer with complementarily reactive alkoxyamine side chains and dibutyl phthalate as a plasticizer were prepared and their crosslinking behavior was observed at 100 degrees C.

Reversible bonds and interactions have been utilized to build stimuli-responsive and reorganizable polymer networks that show recydability, plasticity, and self-healing. In addition, reorganization of polymer gels at ambient temperature, such as room or body temperature, is expected to lead to several biomedical applications. Although these stimuli-responsive properties originate from the reorganization of the polymer networks, not such microscopic structural changes but instead only macroscopic properties have been the focus of previous work. In the present work, the reorganization of gel networks with diarylbibenzofuranone (DABBF)-based dynamic covalent linkages in response to the ambient temperature was systematically investigated from the perspective of both macroscopic and microscopic changes. The gels continued to swell in suitable solvents above room temperature but attained equilibrium swelling in nonsolvents or below room temperature because of the equilibrium of DABBF linkages, as supported by electron paramagnetic resonance measurements. Small-angle X-ray scattering measurements revealed the mesh sizes of the gels to be expanded and the network structures reorganized under control at ambient temperature.

Plasticizer-promoted thermal crosslinking reactions of an alkoxyamine-appended poly(methyl methacrylate)-based dynamic covalent polymer were successfully performed under bulk conditions. The films of the dynamic covalent polymer with complementarily reactive alkoxyamine side chains and dibutyl phthalate as a plasticizer were prepared and their crosslinking behavior was observed at 100 degrees C.

Aromatic disulfide bonds become dynamic in a radical process under weak intensity photoirradiation and can undergo metathesis. Aryl disulfide-containing dynamic covalent polyurethanes were prepared by the polyaddition of disulfide-containing diol and diisocyanate compounds. To determine the dynamic nature of the aryl disulfide-containing polymers, insertion metathesis depolymerization was performed under weak intensity photoirradiation at room temperature. The molecular weights of the dynamic covalent polymers decreased as the irradiation time increased.

We report the preparation of amphiphilic block copolymer micelles with dynamic covalent bonds as autonomously exchangeable crosslinkers with high tolerance against oxygen. Diarylbibenzofuranone (DABBF) was employed as a crosslinker owing to its durability to oxygen and autonomous exchangeability at ambient temperature. It was confirmed that the amphiphilic block copolymer containing the DABBF unit has the capability to form micelles and can form a crosslinking with an exchangeable structure in the presence of oxygen.

Aromatic disulfide bonds become dynamic in a radical process under weak intensity photoirradiation and can undergo metathesis. Aryl disulfide-containing dynamic covalent polyurethanes were prepared by the polyaddition of disulfide-containing diol and diisocyanate compounds. To determine the dynamic nature of the aryl disulfide-containing polymers, insertion metathesis depolymerization was performed under weak intensity photoirradiation at room temperature. The molecular weights of the dynamic covalent polymers decreased as the irradiation time increased.

We report the preparation of amphiphilic block copolymer micelles with dynamic covalent bonds as autonomously exchangeable crosslinkers with high tolerance against oxygen. Diarylbibenzofuranone (DABBF) was employed as a crosslinker owing to its durability to oxygen and autonomous exchangeability at ambient temperature. It was confirmed that the amphiphilic block copolymer containing the DABBF unit has the capability to form micelles and can form a crosslinking with an exchangeable structure in the presence of oxygen.

This book covers a wide range of topics related to functional dyes, from synthesis and functionality to application. Making a survey of recent progress in functional dye chemistry, it provides an opportunity not only to understand the structure-property relationships of a variety of functional dyes but also to know how they are applied in practical use, from electronic devices to biochemical analyses. From classic dyes such as cyanines, squaraines, porphyrins, phthalocyanines, and others to the newest functional π-conjugation systems, various types of functional dyes are dealt with extensively in the book, focusing especially on the state of the art and the future. Readers will benefit greatly from the scientific context in which organic dyes and pigments are comprehensively explained on the basis of chemistry.

平衡系の共有結合をもつ分子構造体は,共有結合が組み換わることで,可逆的な分子間相互作用により形成された分子集合体と同じように,置かれた環境に応じてより安定な構造へと変化する。このような可逆的な共有結合の平衡系を活用した化学システムは「動的共有結合化学」と呼ばれている。動的共有結合化学の考え方を高分子に導入すると,高分子の特性は大きく変化する。本稿では,自在に構造変換できる高分子を指向した「動的共有結合ポリマー」の開発について解説する。

動的共有結合化学に基づくネットワーク構造を有するゲルは，外部刺激に応答して魅力的な機能を示すことが知られている。本稿では，動的共有結合化学の中でも特殊な，室温・空気中という穏和な環境下において可逆的な解離・結合の平衡状態にある炭素－炭素共有結合に着目し，この結合を高分子ネットワーク中に組み込んだゲルが示すいくつかの興味深い特性に関して紹介する。この動的共有結合ポリマーゲルは，室温や体温付近の穏和な温度でネットワークの構造再編成を自発的に行い，さらにこの性質と可逆的な炭素－炭素結合の小さな解離エネルギーに起因した自己修復性を示す。また，解離により生成するラジカルが空気中でも比較的安定であり，青色を示すことから，ゲル中の高分子鎖に印加された応力，特に溶媒の凝固により高分子鎖に生じる応力の繰り返し可視化も可能である。 It is well known that polymeric gels based on dynamic covalent chemistry can exhibit unique properties in response to external stimuli. Here we show fascinating properties of dynamic covalent polymer gels, in which reversible carbon－carbon bonds in equilibrium between dissociation and association at room temperature in air are embedded. The dynamic covalent polymer gels have the ability to reorganize their polymer networks autonomously at ambient temperature, and therefore, can show self-healing also due to the small bond dissociation energy. In addition, the tolerance of the blue-colored carbon radicals, which are formed from the cleavage of the carbon－carbon reversible bonds, toward oxygen enables the gels to show repeatable stress-visualization, particularly in response to the stress induced by coagulation of swelling solvents.

高分子材料の自己修復性は廃棄物の削減のみならず，人の手による修復が困難な用途への応用も期待できる．この修復へのアプローチの一つに，特定の環境下で解離·結合の平衡状態となる動的な共有結合の反応，動的共有結合化学を利用する手法がある．このシステムでは，動的共有結合を高分子材料中に組み込み，この結合の組み換え反応とそれに伴う高分子ネットワークの構造再編成により修復が進行するため，理論上は分子レベルでの修復が可能となり，修復回数に制限がないという利点を有する．熱や光，触媒といったさまざまな外部刺激で平衡状態に到達する反応系，あるいは外部刺激なしに，室温·空気中で平衡状態にある反応系を利用することで，高分子材料の自己修復が可能となることがこれまで報告されている．本稿では，このような動的共有結合化学に基づく高分子材料の自己修復に関して解説する． Self-healing materials attract a lot of attention due to their ability to repair the internal and external damage, thereby extending the lifetime of the materials in numerous applications that we cannot repair easily. A system using dynamic covalent chemistry is useful to achieve self-healing in polymeric materials, because this system enables healing at the molecular level and an unlimited number of healing times.  To date, many kinds of exchange reactions of dynamic covalent bonds that are driven by heating, light irradiation, or adding catalyst have been utilized for the healing. In this paper, we review such self-healing polymeric materials based on dynamic covalent chemistry.