Self-healing and shape-memory polymers based on cellulose acetate matrix.

The creation of self-healing polymers with superior strength and stretchability from biodegradable materials is attracting increasing attention. In this study, we synthesized new biomass-derived cellulose acetate (CA) derivatives by ring-opening graft polymerization of δ-valerolactone followed by the introduction of ureidopyrimidinone (Upy) groups in the polymer side chains. Due to the semicrystalline aliphatic characteristics of the side chain poly(δ-valerolactone) (PVL) and quadruple hydrogen bonds formed by the Upy groups, the stretchability of the resulting polymers was significantly enhanced. Moreover, the shape memory ability and self-healing property (58.3% of self-healing efficiency) were successfully imparted to the polymer. This study demonstrates the great significance of using biomass sources to create self-healing polymers.

This paper describes the first successful demonstration of self-healing polymers with superior strength and stretchability from a biodegradable material, cellulose acetate (CA). We initially introduced the ureidopyrimidinone (Upy) groups in the side chains of CA. However, the resulting polymer was not soluble and processable. In order to solve this issue, a new strategy based on the ring-opening graft polymerization of δ-valerolactone followed by the introduction of ureidopyrimidinone (Upy) groups was adopted. Due to the semicrystalline aliphatic characteristics of the side chain poly(δ-valerolactone) (PVL), the resulting polymers were soluble and processable. In addition, the quadruple hydrogen bonds formed by the Upy groups enhanced the stretchability of the resulting polymers. Moreover, the shape memory ability and self-healing property were successfully achieved due to the presence of PVL and Upy. The developed new strategy can be applied to a variety of polymers including biomass-based polymers and materials.

A Route to Conjugated Monomers and Polymers Incorporating 2,5-Connected Oxazole in the Backbone.

Joining of imidazole, pyrimidine, and oxazole to other conjugated core units was explored in pursuit of yielding monomers to synthesize organic semiconducting polymers. Regioregular oxazole-flanked thiophene, benzothiadiazole, naphthalene diimide (NDI), and thienopyrroledione (TPD) were successfully isolated via stannylation of oxazole and the Stille coupling of brominated core units (overall yields ranging from ca. 40 to 60%). From subsequent direct arylation polymerization, NDI/oxazole/TPD-containing regioisomeric polymers were obtained with optical and electrochemical orbital energetics in the semiconducting regime.

Organic J-Aggregate Nanodots with Enhanced Light Absorption and Near-Unity Fluorescence Quantum Yield.

Development of biocompatible fluorophores with small size, bright fluorescence, and narrow spectrum translate directly into major advances in fluorescence imaging and related techniques. Here, we discover that a small donor-acceptor-donor-type organic molecule consisting of a carbazole (Cz) donor and benzothiazole (BT) acceptor (CzBTCz) assembles into quasi-crystalline J-aggregates upon a formation of ultrasmall nanoparticles. The 3.5 nm CzBTCz Jdots show a narrow absorption spectrum (fwhm = 27 nm), near-unity fluorescence quantum yield (ϕfl = 0.95), and enhanced peak molar extinction coefficient. The superior spectroscopic characteristics of the CzBTCz Jdots result in two orders of magnitude brighter photoluminescence of the Jdots compared with semiconductor quantum dots, which enables continuous single-Jdots imaging over a 1 h period. Comparison with structurally similar CzBT nanoparticles demonstrates a critical role played by the shape of CzBTCz on the formation of the Jdots. Our findings open an avenue for the development of a new class of fluorescent nanoparticles based on J-aggregates.

Millimeter-Deep Detection of Single Shortwave-Infrared-Emitting Polymer Dots through Turbid Media.

Fluorescence imaging at longer wavelengths, especially in the shortwave-infrared (SWIR: 1000-1700 nm) region, leads to a substantial decrease in light attenuation, scattering, and background autofluorescence, thereby enabling enhanced penetration into biological tissues. The limited selection of fluorescent probes is a major bottleneck in SWIR fluorescence imaging. Here, we develop SWIR-emitting nanoparticles composed of donor-acceptor-type conjugated polymers. The bright SWIR fluorescence of the polymer dots (primarily attributable to their large absorption cross-section and high fluorescence saturation intensity (as high as 113 kW·cm-2)) enables the unprecedented detection of single particles as small as 14 nm through millimeter-thick turbid media. Unlike most SWIR-emitting nanomaterials, which have an excited-state lifetime in the range of microseconds to milliseconds, our polymer dots exhibit a subnanosecond excited-state lifetime. These characteristics enable us to demonstrate new time-gated single-particle imaging with a high signal-to-background ratio. These findings expand the range of potential applications of single-particle deep-tissue imaging.

Significant Improvement of Unipolar n-Type Transistor Performances by Manipulating the Coplanar Backbone Conformation of Electron-Deficient Polymers via Hydrogen Bonding.

The development of high-performance unipolar n-type semiconducting polymers still remains a significant challenge. Only a few examples exhibit a unipolar electron mobility over 5 cm2 V-1 s-1. In this study, a series of new poly(benzothiadiazole-naphthalenediimide) derivatives with a high unipolar electron mobility (µe) up to 7.16 cm2 V-1 s-1 in thin-film transistors are reported. The dramatically increased µe is achieved by finely optimizing the coplanar backbone conformation through the introduction of vinylene bridges, which can form intramolecular hydrogen bonds with the neighboring fluorine and oxygen atoms. The hydrogen-bonding functionalities are fused to the backbone to ensure a much more planar conformation of the conjugated π-system, as demonstrated by the density functional theory (DFT)-based calculations. The theoretical prediction is in good agreement with the experimental results. As the coplanarity is promoted by the hydrogen bonding, the thin-film crystallinity and molecular packing strength are also improved, which is evidenced by the synchrotron two-dimensional grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) measurements. Notably, the GIWAXS measurements reveal an extremely short π-π stacking distance of 3.40 Å. Overall, this study marks a significant advance in the unipolar n-type semiconducting polymers and offers a general approach for further increasing the electron mobility of semiconducting polymers in organic electronics.

Efficient Inverted Perovskite Solar Cells by Employing N-Type (D-A1 -D-A2 ) Polymers as Electron Transporting Layer.

It is highly desirable to employ n-type polymers as electron transporting layers (ETLs) in inverted perovskite solar cells (PSCs) due to their good electron mobility, high hydrophobicity, and simplicity of film forming. In this research, the capability of three n-type donor-acceptor1 -donor-acceptor2 (D-A1 -D-A2 ) conjugated polymers (pBTT, pBTTz, and pSNT) is first explored as ETLs because these polymers possess electron mobilities as high as 0.92, 0.46, and 4.87 cm2 (Vs)-1 in n-channel organic transistors, respectively. The main structural difference among pBTT, pBTTz, and pSNT is the position of sp2 -nitrogen atoms (sp2 -N) in the polymer main chains. Therefore, the effect of different substitution positions on the PSC performances is comprehensively studied. The as-fabricated p-i-n PSCs with pBTT, pBTTz, and pSNT as ETLs show the maximum photoconversion efficiencies of 12.8%, 14.4%, and 12.0%, respectively. To be highlighted, pBTTz-based device can maintain 80% of its stability after ten days due to its good hydrophobicity, which is further confirmed by a contact angle technique. More importantly, the pBTTz-based device shows a neglected hysteresis. This study reveals that the n-type polymers can be promising candidates as ETLs to approach solution-processed highly-efficient inverted PSCs.

Significant Difference in Semiconducting Properties of Isomeric All-Acceptor Polymers Synthesized via Direct Arylation Polycondensation.

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon-hydrogen (C-H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high-molecular-weight all-acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co-catalysts. We thus obtained two isomeric all-acceptor polymers, P1 and P2, which have the same backbone and side-chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge-transport properties. P2 with a greater backbone torsion has favorable edge-on orientations and a high electron mobility µe of 2.55 cm2 V-1 s-1 . Moreover, P2-based transistors show an excellent shelf-storage stability in air even after the storage for 1 month.

Covalent layer-by-layer thin films with charge-transfer chromophores: side chain engineering for efficient Ag+ ion recognition in aqueous solutions.

Covalent layer-by-layer (LbL) thin films are fabricated by a highly efficient [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction of aniline-substituted alkyne and 7,7,8,8-tetracyanoquinodimethane (TCNQ) moieties. Polystyrene bearing aniline-substituted alkyne side chains and TCNQ polyester were prepared as precursor polymers, then sequentially deposited and fixed by covalent bonds on an indium-tin-oxide (ITO) substrate. The successful alternate growth of the films was demonstrated by many techniques including absorption spectroscopy, surface roughness, and redox activities. Interestingly, the water contact angles of the film surface were dependent on the side chains of the polystyrene derivatives. When hydrophilic triethylene glycol was employed, the surface hydrophilicity was similar to that of the TCNQ polyester. In contrast, the use of hydrophobic n-hexyl groups resulted in a significant difference in the water contact angles between the polystyrene and TCNQ polyester. A similar difference occurred when the Ag+ ion recognition was studied by soaking the LbL films in aqueous solutions. The LbL films constructed from the polystyrene with triethylene glycol chains displayed a more rapid and significant recognition of Ag+ ions than those constructed from the polystyrene with n-hexyl chains.

The [2+2] Cycloaddition-Retroelectrocyclization (CA-RE) Click Reaction: Facile Access to Molecular and Polymeric Push-Pull Chromophores.

The [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction between electron-rich alkynes and electron-deficient alkenes is an efficient procedure to create nonplanar donor-acceptor (D-A) chromophores in both molecular and polymeric platforms. They feature attractive properties including intramolecular charge-transfer (ICT) bands, nonlinear optical properties, and redox activities for use in next-generation electronic and optoelectronic devices. This Review summarizes the development of the CA-RE reaction, starting from the initial reports with organometallic compounds to the extension to purely organic systems. The structural requirements for rapid, high-yielding transformations with true click chemistry character are illustrated by examples that include the broad alkyne and alkene substitution modes. The CA-RE click reaction has been successfully applied to polymer synthesis, with the resulting polymeric push-pull chromophores finding many interesting applications.

Cross-linking and postfunctionalization of polymer films by utilizing the orthogonal reactivity of 7,7,8,8-tetracyanoquinodimethane.

Cross-linked polymer films are prepared by the alternating copolymerization of 4-chloromethylstyrene and 7,7,8,8-tetracyanoquinodimethane comonomers, which is followed by the postfunctional surface modification with donor-acceptor chromophores or redox active components using click chemistry reactions.

3,6-Carbazole vs 2,7-carbazole: A comparative study of hole-transporting polymeric materials for inorganic-organic hybrid perovskite solar cells.

The ever increasing demand for clean energy has encouraged researchers to intensively investigate environmentally friendly photovoltaic devices. Inorganic-organic hybrid perovskite solar cells (PSCs) are very promising due to their potentials of easy fabrication processes and high power conversion efficiencies (PCEs). Designing hole-transporting materials (HTMs) is one of the key factors in achieving the high PCEs of PSCs. We now report the synthesis of two types of carbazole-based polymers, namely 3,6-Cbz-EDOT and 2,7-Cbz-EDOT, by Stille polycondensation. Despite the same chemical composition, 3,6-Cbz-EDOT and 2,7-Cbz-EDOT displayed different optical and electrochemical properties due to the different connectivity mode of the carbazole unit. Therefore, their performances as hole-transporting polymeric materials in the PSCs were also different. The device based on 2,7-Cbz-EDOT showed better photovoltaic properties with the PCE of 4.47% than that based on 3,6-Cbz-EDOT. This could be due to its more suitable highest occupied molecular orbital (HOMO) level and higher hole mobility.

Efficient Synthesis and Photosensitizer Performance of Nonplanar Organic Donor-Acceptor Molecules.

Nonplanar organic donor-acceptor molecules bearing a carboxylic acid group were synthesized by the formal [2+2] cycloaddition-retroelectrocyclization reaction between aniline-substituted alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). This reaction offers an atom-economic one-step approach to donor-acceptor chromophores in satisfactory high yields. The resulting donor-acceptor molecules were characterized by conventional analytical techniques. In addition, the nonplanarity and intermolecular interactions were investigated by X-ray crystallography. The energy levels and intramolecular charge-transfer (CT), evaluated by UV-Vis-near IR spectroscopy and electrochemistry, suggested that there is a linear correlation between the optical and electrochemical band gaps. Based on these structural and electronic analyses, the photosensitizer performances of the donor-acceptor molecules in dye-sensitized solar cells (DSSCs) were initially investigated using TiO2 or SnO2 electrodes. Although the power conversion efficiencies were limited, the incident-photon-to-current-conversion efficiency (IPCE) spectra indicated a better photocurrent generation for the devices on SnO2 as compared to those on TiO2.

Enhanced Photothermal Property of NDI-Based Conjugated Polymers by Copolymerization with a Thiadiazolobenzotriazole Unit.

Solar steam generation (SSG) is a promising photothermal technology to solve the global water storage issue. The potential of π-conjugated polymers as photothermal materials is significant, because their absorption range can be customized through molecular design. In this study, naphthalenediimide (NDI) and thiadiazolobenzotriazole (TBZ) were employed as bifunctional monomers to produce conjugated polymers. There are two types of polymers, P1 and P2. P1 is based on NDI, while P2 is a copolymer of NDI and TBZ in a ratio of 9:1. Both polymers had high molecular weights and sufficient thermal stability. UV-vis-near-infrared (NIR) absorption spectra revealed that both polymers have large extinction coefficients ascribed to the NDI and TBZ chromophores. Notably, the absorption spectrum of P2 exhibited a significant red shift compared to P1, resulting in a narrow optical bandgap and absorption in the NIR range. This result suggested that P2 has a higher light absorption than P1. Photoluminescence (PL) spectra were measured to elucidate the conversion of the absorbed light into thermal energy. It was found that P2 has a reduced fluorescence quantum yield as a result of the TBZ unit, signifying a proficient conversion of the photothermal energy. Based on the results, it appears that the P2 film has a greater photothermal property compared to that of the P1 film. The surface temperature of the P2 film reached approximately 50 °C under the investigated conditions. In addition, copolymer P2 exhibited an impressive SSG efficiency of 72.4% under 1 sun (1000 W/m2) irradiation. All the results suggested that narrow bandgap conjugated polymers containing the TBZ unit are highly effective materials for achieving optimal performance in SSGs.

Structural requirements for producing solvent-free room temperature liquid fullerenes.

A new class of solvent-free room temperature liquid fullerenes was synthesized by attaching a single substituent of 1,3,5-tris(alkyloxy)benzene unit to C60 or C70 under the Prato conditions. Although the C60 monoadducts were single components after chromatographic purification, the C70 monoadducts were isomeric mixtures due to the prolate spheroidal π-chromophore. The alkyl chain length of the substituents significantly affected both melting points and rheological behavior of the fullerene derivatives. When the alkyl chains were short, the intermolecular π-π interactions of adjacent fullerene cores led to a melting point higher than room temperature. In contrast, in the case of exceedingly long alkyl chains, such as eicosyl (-C20H41) and docosanyl (-C22H45) groups, the van der Waals interactions among neighboring alkyl chains became dominant. Accordingly, only medium alkyl chain lengths could provide solvent-free fluidic fullerenes with low melting points. The rheological measurements of the liquid fullerenes at 25 °C revealed their unique liquid characteristics; molecular-level friction (or viscosity) and nanometer-scale clustering were noticed. It is generally thought that alkyl chains serve as a stabilizer of the fullerene core units. Thus, a longer chain or higher plasticity of the stabilizers would promote the disturbance of the core-core interactions. It was indeed shown that longer alkyl chains resulted in a lower fluid viscosity. It was also found that metastable solid phases were produced by the noticeable van der Waals interaction between the long alkyl chains especially when a symmetric C60 core was adopted. This interesting finding enabled the comparison of electrochemical activities of the C60 unit between the solvent-free liquid and metastable solid form, which revealed a superior electrochemical activity in the liquid state.

Polymeric ion sensors with multiple detection modes achieved by a new type of click chemistry reaction.

The rapid growth of the click chemistry concept enables the production of a wide variety of functional polymers. Among the new generation of click chemistry reactions, the highly efficient addition reactions between electron-rich alkynes and cyano-based acceptors, referred to as alkyne-acceptor click chemistry, have found promising application possibilities as polymeric chemosensors. The donor-acceptor chromophores, formed by this click chemistry reaction, feature intense charge-transfer (CT) bands in the visible region, but they are hardly fluorescent. Importantly, the chromophores possess two different nitrogen atoms, namely the aniline nitrogen and cyano nitrogen. The recognition of some specific metal cations by different nitrogen atoms in the polymers led to different modes of changes in the absorption spectra. For example, the hard acid of Fe(3+) ion was recognized by the aniline nitrogen, resulting in a decrease in the CT bands. On the other hand, the soft acid of the Ag(+) ion was captured by the cyano nitrogen, leading to a bathochromic shift in the CT bands. Some specific anions, such as CN(-), F(-), and I(-) ions, were also recognized by a chemodocimetric detection mode, discoloring the original solutions. When the CT bands decreased upon the addition of analytes, the polymers were found to serve as turn-on fluorescent sensors. In this perspective, the detailed detection modes of the new polymeric chemosensors are fully described.

PEDOT:PSS versus Polyaniline: A Comparative Study of Conducting Polymers for Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) based on conducting polymers have attracted significant attention in the field of biosensors. PEDOT:PSS and polyaniline (PANI) are representative conducting polymers used for OECTs. While there are many studies on PEDOT:PSS, there are not so many reports on PANI-based OECTs, and a detailed study to compare these two polymers has been desired. In this study, we investigated the fabrication conditions to produce the best performance in the OECTs using the above-mentioned two types of conducting polymers. The two main parameters were film thickness and film surface roughness. For PEDOT:PSS, the optimal conditions for fabricating thin films were a spin-coating rate of 3000 rpm and a DI water immersion time of 18 h. For PANI, the optimal conditions were a spin-coating rate of 3000 rpm and DI water immersion time of 5 s, and adding dodecylbenzenesulfonic acid (DBSA) was found to provide better OECT performances. The OECT performances based on PEDOT:PSS were superior to those based on PANI in terms of conductivity and transconductance, but PANI showed excellence in terms of film thickness and surface smoothness, leading to the good reproducibility of OECT performances.

Conjugated photothermal materials and structure design for solar steam generation.

With the development of solar steam generation (SSG) for clean water production, conjugated photothermal materials (PTMs) have attracted significant interest because of their advantages over metallic and inorganic PTMs in terms of high light absorption, designable molecular structures, flexible morphology, and solution processability. We review here the recent progress in solar steam generation devices based on conjugated organic materials. Conjugated organic materials are processed into fibers, membranes, and porous structures. Therefore, nanostructure design based on the concept of nanoarchitectonics is crucial to achieve high SSG efficiency. We discuss the considerations for designing SSG absorbers and describe commonly used conjugated organic materials and structural designs.

Improved supercapacitor performances by adding carbonized C60-based nanospheres to PVA/TEMPO-cellulose hydrogel-based electrolyte.

With the emergence of the energy crisis and the development of flexible electronics, there is an urgent need to develop new reliable energy supply devices with good flexibility, stable energy storage, and efficient energy transfer. Porous carbon materials have been proven to enhance the efficiency of ion transport, as the nanospaces within them serve as pathways for mass transport. However, they have been mainly investigated in the electrodes of supercapacitors and batteries. To elucidate their function in the solid electrolytes, we introduced C60-based carbonized nanospheres into PVA/TEMPO-cellulose-based hydrogels by exploiting the electrostatic interaction between the carboxyl groups of TEMPO-cellulose and the carbonized nanospheres. The obtained hydrogels were further utilized as the solid electrolytes for the supercapacitors. Through a comprehensive investigation, we found that the carbonized nanospheres can act as physical crosslinking points and increase the maximum stress of the hydrogel from 0.12 to 0.31 MPa without affecting the maximum strain. In addition, the nanospaces of the carbonized nanospheres provided a pathway for ion transport, improving the capacitance of the supercapacitor from 344.83 to 369.18 mF cm-2 at 0.5 mA cm-2. The capacitance retention was also improved from 53% to 62% at 10 mA cm-2. Collectively, this study provides new insights into the application of carbonized materials to solid electrolytes.

Click Synthesis of Triazole Polymers Based on Lignin-Derived Metabolic Intermediate and Their Strong Adhesive Properties to Cu Plate.

2-Pyrone-4,6-dicarboxylic acid (PDC) is a chemically stable metabolic intermediate of lignin that can be produced on a large scale by transforming bacteria. Novel biomass-based polymers based on PDC were synthesized by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and fully characterized by nuclear magnetic resonance, infrared spectroscopies, thermal analysis, and tensile lap shear strength measurements. The onset decomposition temperatures of these PDC-based polymers were all above 200 °C. In addition, the PDC-based polymers exhibited strong adhesive properties to various metal plates, with the highest adhesion to a copper plate of 5.73 MPa. Interestingly, this result was in contrast to our previous findings that PDC-based polymers weakly adhere to copper. Furthermore, when bifunctional alkyne and azide monomers were polymerized in situ under hot-press conditions for 1 h, the resulting PDC-based polymer displayed a similar adhesion to a copper plate of 4.18 MPa. The high affinity of the triazole ring to copper ions improved the adhesive ability and selectivity of the PDC-based polymers to copper while still maintaining the strong adhesive ability to other metals, which is conducive to enhancing the versatility of PDC-based polymers as adhesives.