Photo-responsive linear and cross-linked supramolecular polymers based on host–guest interactions

Open AccessCCS ChemistryRESEARCH ARTICLE1 Apr 2020Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains Jing Ma†, Jianwu Tian†, Zitong Liu, Dandan Shi, Xisha Zhang, Guanxin Zhang and Deqing Zhang Jing Ma† Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) University of Chinese Academy of Sciences, Beijing 100049, (China) , Jianwu Tian† Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) University of Chinese Academy of Sciences, Beijing 100049, (China) , Zitong Liu *Corresponding author: E-mail Address: [email protected]; E-mail Address: [email protected]; Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) , Dandan Shi Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) University of Chinese Academy of Sciences, Beijing 100049, (China) , Xisha Zhang Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) University of Chinese Academy of Sciences, Beijing 100049, (China) , Guanxin Zhang Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) and Deqing Zhang *Corresponding author: E-mail Address: [email protected]; E-mail Address: [email protected]; Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Center of Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, (China) University of Chinese Academy of Sciences, Beijing 100049, (China) https://doi.org/10.31635/ccschem.019.201900056 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-responsive polymeric semiconductors through the incorporation of spiropyran (SP) groups in the polymer side chains. The semiconducting performances of resultant FETs with a diketopyrrolopyrroles (DPP)-based conjugated donor–acceptor (D–A) polymer, that entails SP units in the side chains ( pDSP-1), could be modulated reversibly through UV and visible light irradiations, or UV light irradiation and heating, or acid treatment and heating. Our studies reveal that during the reversible transformations of closed, open, and the protonated forms of spiropyran, achieved by light irradiations, heating, and under acidic conditions, a large dipole moment changes occur, which triggers the reversible variation of semiconducting performance of the FETs. Download figure Download PowerPoint Introduction In the last few decades, the rapid developments of organic and polymeric semiconductors with high charge mobilities have been witnessed.1–5 Newly conjugated molecules and polymers have been designed, synthesized, and new device fabrication methods have been proposed in order to improve the semiconducting performance of organic semiconductors.6–20 Thin-film field-effect transistors (FETs) based on organic/polymeric semiconductors have shown potential applications in memory devices, flexible displays, and wearable electronics.21–24 In recent years, FETs with external-field tunable electrical properties other than electrical voltage have been of considerable interest.25–40 Since the output current could be controlled simultaneously and independently by voltage, as well as other external fields, it is possible to integrate complex functionalities, such as memory devices, switches, and complex logic operations, in a single FET device.41–43 Often, light is used as the external stimuli for optically tunable FETs.22–40 In fact, their fabrications have been achieved by utilizing photochromic molecules, able to undergo reversible light-induced interconversions between two isomers.41 For instance, Samorì and co-workers25 blended diarylethene derivative with P3HT [poly(3-hexylthiophene)] to generate a semiconducting film, which showed optically reversible FET with characteristic bi-stable states upon alternating UV and visible light irradiations. Additionally, Nuckolls and co-workers26 built optically reversible FETs using spiropyrans (SP) in the dielectric layer. Further, recent work by our lab and others27 incorporated azobenzene groups into the flexible alkyl side chains of a conjugated polymer, which was used successfully to fabricate optically tunable FETs with rapid photoresponsiveness. In addition to light, other external inputs, such as heating and introducing chemical species are also of high interest in the generation of multi-stimuli-responsive FETs.44–46 Herein, we report the fabrication of multi-stimuli-responsive FETs with the semiconducting D–A polymer (diketopyrrolopyrrole (DPP)-quaterthiophene conjugated polymer) with the substituted photochromic SP groups in the side chains ( pDSP-1), shown in Scheme 1. The incorporation of SP into the D–A polymer was based on the following considerations: (1) The closed-form, SP, should transform reversibly into the open-form, merocyanine (MC), and the protonated merocyanine (MCH+) forms, after UV or visible light irradiations, heating, addition of acid, and even the application of mechanical force.47,48 (2) By comparison, the open-form, MC, must possess a larger dipole moment (∼17.7 D) than the untransformed, closed-SP-form (∼4.3 D).49 Such a change in the dipole moment, presumably, generates carrier scattering sites within the semiconducting thin film and; as a result, the charge transporting behavior should be reduced. Thus, this became the basis of our fabrication of multi-stimuli-responsive FETs coupled with pDSP-1. Beside, pDSP-1 is a typical diketopyrrolopyrroles (DPP)-based conjugated donor–acceptor (D–A) polymer, which is known for its high charge mobility and good photostability.50–54 In pDSP-1, the SP moieties were incorporated into the side chains through covalent bonding; accordingly, the SP units were distributed uniformly within the semiconducting layer, and thus, the stability of the resulting device was enhanced. In comparison, SP was used in constructing responsive FETs via physical blending with the semiconducting polymer or by interfacial/dielectric modifications.26,30–35 The results revealed that the current and performance of the thin FETs coupled with pDSP-1 device could be reversibly tuned in a relatively faster manner by alternating UV and visible light irradiations, or by UV light irradiation, followed by heating, or by addition of acid, followed by heating. Scheme 1 | Chemical structure of pDSP-1 and the schematic representation of the multi-stimuli-responsive FET architecture. For comparative mechanistic studies, pDSP-5, containing different contents of SP groups in the side chains, was also prepared. Download figure Download PowerPoint Results and Discussion Synthesis and characterization of pDSP-1 The SP side chains conjugated DPP-based D–A polymer, pDSP-1, was prepared by Stille co-coupling of compounds 3 (with SP-containing linear alkyl chains) and 4 (with branching alkyl chains) with the bis(stannyl) compound 5 (see ). The molar ratio of compounds 3 and 4 was set at 1∶1 to enable the formation of the polymer pDSP-1, in which the molar ratio of the linear chains with SP units versus the branching alkyl chains is 1∶1. For comparison (see below), the polymer, pDSP-5, for which the molar ratio of the linear chains with SP units versus the branching alkyl chains was decreased to 1∶5, was prepared under similar conditions. After purification, pDSP-1 and pDSP-5 were obtained in 80% and 87% yields, respectively. pDSP-1 and pDSP-5 were characterized by 1H NMR, solid 13C NMR, and by elemental analysis. The molar ratios of SP-containing side chains versus branching side chains in pDSP-1 and pDSP-5 were calculated to be ∼1.09∶1 and ∼1∶4.67, being close to the respective feed ratios, based on the elemental analysis data. The number averaged molecular weights (Mns) and polydispersities (PDIs) of pDSP-1 and pDSP-5, determined by high-temperature gel permeation chromatography in o-dichlorobenzene at 140 °C, were 16.8 kg mol−1 and 2.9, and 26.0 kg mol−1 and 1.4, respectively. pDSP-1 and pDSP-5 could be dissolved in 1,1,2,2-tetrachloroethane (TeCA) to reach a concentration of ∼5 mg mL−1 at 100 °C. They could not dissolve in chloroform and nonhalogenated solvents, such as toluene and tetrahydrofuran (THF). Both pDSP-1 and pDSP-5 were thermally stable with decomposition temperatures of 309 °C and 371 °C (at a weight loss of 5%) based on thermogravimetric analysis (TGA) data (). Apparently, the incorporation of SP units in the side chains did not affect the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) levels of pDSP-1 and pDSP-5. On the basis of cyclic voltammograms obtained from cyclic voltammetry (CV) analysis (), the HOMO/LUMO energy levels of pDSP-1 and pDSP-5 were estimated to be −5.18/−3.69 and −5.22/−3.67 eV, respectively (), being close to those of DPP-based D–A polymers reported previously.55–57 Absorption spectral variations for pDSP-1 upon light irradiations, heating, and protonation The SP groups in pDSP-1 were expected to switch reversibly between the closed-form (SP) and the opened form (MC) upon UV and visible light irradiations. As shown in , new absorption peaks in the range of 500–600 nm appeared in the UV-vis absorption spectrum after UV light irradiation of a solution of pDSP-1, and these peaks disappeared after further application of visible light irradiation or heating the solution. Similarly, new absorptions peaks ∼420 nm were observed for the solution of pDSP-1 after the addition of trifluoroacetic acid (TFA or CF3COOH) (see ), and these absorptions disappeared after heating the solution further. We attributed the absorption at ∼420 nm to the formation of the MCH+ form, based on previous reports.47,48 Additionally, such absorption spectral changes could be reversibly repeated for 5 cycles. Moreover, the correlation of the absorption spectral variations with the transformations of SP into MC or MCH+ forms also matched with the data obtained for thin films of pDSP-1. Figure 1a shows the absorption spectra of thin film of pDSP-1 before and after UV light irradiation at 365 nm for 30 s, followed by exposure to visible light irradiation at 470 nm for 10 min. A new absorption at ∼590 nm emerged after UV light irradiation. According to previous studies,47,48 the absorption from 550 to 600 nm is due to the formation of the MC form. Furthermore, visible light irradiation resulted in the gradual decrease of the absorption at 590 nm (see Figure 1b). Visible light irradiation for 10 min was required for the complete disappearance of the absorption due to the MC form. In contrast, this 590 nm peak due to the MC form disappeared quickly after heating the thin film of pDSP-1 at 80 °C for 2 min, as shown in Figure 1c. Indeed, the reversible variation of the absorption at 590 nm for thin film of pDSP-1 could be repeated for five cycles after alternating UV light irradiation and heating at 80 °C, as depicted in Figure 1d. These results indicate that the reversible interconversion between the SP form in pDSP-1 and MC form occurs at fast rates upon UV light irradiation and heating at 80 °C. Moreover, new absorption around 420 nm appeared after the thin film of pDSP-1 was treated with the vapor of TFA (500 ppm for 1 min), and this new peak vanished after further heating at 80 °C for 5 min (Figure 1e,f). We used monomer 3 (see ) as a model for pDSP-1 and pDSP-5 to estimate the conversion ratio by 1H NMR. The 1H NMR spectra of monomer 3 and those after UV light irradiation and treatment with CF3COOD are shown in , respectively. The chemical shifts around 8.65–8.60 ppm, 7.79–7.58, and 6.67–6.64 ppm were due to the MC form (see ), whereas the chemical shifts around 8.50 ppm, 8.29–8.16 ppm, and 7.64 ppm were attributable to the MCH+ form. Based on these 1H NMR data, ∼39.5% of SP units were converted to the MC form after UV irradiation at 365 nm for 30 s. Similarly, ∼82.5% SP units were transformed into the MCH+ moieties after addition of 0.03 M deuterium TFA (d-TFA or CF3COOD). However, the estimated conversion ratios might not reflect the conversion efficiencies of SP into MC (after UV light irradiation) and SP into MCH+ (after treatment with CF3COOH) in thin films of pDSP-1 and pDSP-5. This is because the structures of monomer 3 and pDSP-1/ pDSP-5 are different; thus, their conversion efficiencies are expected to be different both in solution and as thin films. Figure 1 | UV-vis absorption spectra of thin film of pDSP-1: (a) After successive UV light (365 nm for 30 s) and visible light (470 nm for 10 min) irradiations for five cycles. (b) The reversible variations of absorption intensity at 590 nm after alternating UV and visible irradiations. (c) After successive UV light irradiation (365 nm for 30 s) and heating (80 °C for 2 min) for five cycles. (d) The reversible variations of absorption intensity at 590 nm after alternating UV and heating treatments. (e) After successive acid [(CF3COOH) vapor (500 ppm) for 1 min] treatment and heating (80 °C for 5 min) for five cycles. (d) The reversible variations of absorption intensity at 420 nm after alternating acid and heating treatments. Download figure Download PowerPoint Multi-stimuli-responsive FETs We first explored the semiconducting performances of pDSP-1 by fabrication of bottom-gate, bottom-contact (BGBC) FETs before UV light irradiation. Predictably, a thin film of pDSP-1 exhibited a typical p-type semiconducting behavior under ambient conditions based on the transfer and output curves (). As shown in , hysteresis was minimal for the transfer and output characteristics. The maximum/average saturated and linear hole mobilities of thin films of pDSP-1 were measured to be 0.20/0.16 and 0.09/0.07 cm2 V−1 s−1, respectively, after thermal annealing at 160 °C, with on/off ratio of 106–107 (). We further studied the tunable semiconducting properties of FETs with thin films of pDSP-1 after UV light irradiation and heating at 80 °C. Figure 2a and show the transfer and output curves after UV light irradiation at 365 nm for 30 s, followed by heating at 80 °C for 2 min. Undoubtedly, the transfer curve was altered upon UV light irradiation, due to the transformation of the SP moieties of pDSP-1 to MC. Upon heating, the transfer curve was restored, attributable to the conversion of MC to SP. The output curve shows the same tendency (), suggesting that the reversible transformation between SP and MC forms. Such reversible tuning could be repeated for 5 cycles upon the successive UV light irradiation and heating treatment. As shown in Figure 2b and Table 1, the pristine average IDS was measured to be 6.5 × 10−5 A (VGS = VDS = −60 V), and it decreased to 2.1 × 10−5 A after UV light irradiation for 30 s. The drain current increased almost to the initial value after heating the device for 2 min. Figure 2b depicts the reversible variation of the device current for five cycles after alternating UV light irradiation and heating. In addition, the average hole mobility of pDSP-1 thin film could also be reversibly tuned between 0.16 and 0.05 cm2 V−1 s−1. Interestingly, the variation of IDS after UV light irradiation and heating matched well with the variation of the absorption spectra change of pDSP-1 in association with the transformation of the SP and MC forms of SP units in pDSP-1 (Figure 2b). Figure 2 | UV-vis absorption spectra showing: (a) variations in the transfer curves based on different pDSP-1 treatments after alternating UV light irradiation (365 nm for 30 s) and heating (80 °C for 2 min) and (b) the reversible modulation of IDS (VDS = VGS = −60 V) and absorption intensity at 590 nm for five UV/heating cycles. W = 1440 μm, L = 5 μm. I is the drain current upon UV or thermal treatment, while I0 is the initial drain current. A is the absorbance upon UV or thermal treatment, while A0 is the initial absorbance. Download figure Download PowerPoint Table 1 | Average Mobilities (μh), Drain Currents, and Current Variation Ratios for pDSP-1- and pDSP-5-Based FET Devices After UV Light Irradiation or Acid Treatment Polymer μh/cm2 V−1 s−1 I0 Current (10−5 A) Stimulus μh/cm2 V−1 s−1 I Current (10−5 A) Current Variation Ratio (%) pDSP-1 0.16a 6.5a UV 0.05b 2.1b 67d Acid 0.06c 2.3c 65d pDSP-5 0.60a 17.5a UV 0.30b 10.0b 43d Acid 0.28c 9.5c 46d aInitial average mobilities and drain currents (VDS = VGS = −60 V) of pDSP-1 and pDSP-5; baverage mobilities and drain currents after UV irradiations; caverage mobilities and drain currents after acid treatment; dcurrent variation ratio = (I0–I)/I0. We also explored the reversible variations of the semiconducting performances of FETs coupled with pDSP-1 upon either alternating UV and visible light irradiations or alternating acid treatment and heating at 80 °C. As discussed above, the device current and the hole mobility of the thin film of pDSP-1 decreased after UV light irradiation. As shown in Figure 3a,b and , the transfer and output curves for FETs that were treated with UV light, were almost restored to their respective initial ones after further irradiation with visible light at 470 nm for 10 min. Accordingly, the device current (IDS at VGS = VDS = −60 V) was restored to the initial value after further visible light irradiation. Figure 3 | UV-vis absorption spectra showing: (a) variation of transfer curves based on pDSP-1 after alternating UV light (365 nm for 30 s) and visible light (470 nm for 10 min) irradiations; (b) the reversible modulation of IDS (VDS = VGS = −60 V) and absorption intensity at 590 nm for five UV/vis cycles. (c) Variation of transfer curves based on pDSP-1 after alternating acid (500 ppm for 1 min) and heating (80 °C for 5 min) treatment; (d) the reversible modulation of IDS (VDS = VGS = −60 V) and absorption intensity at 420 nm for five acid/heating cycles. W = 1440 μm, L = 5 μm. I is the drain current upon external stimuli treatment, while I0 is the initial drain current. Similarly, A is the absorbance upon external stimuli treatment, while A0 is the initial absorbance. Download figure Download PowerPoint As discussed earlier, and also, displayed in Scheme 1 and Figure 1e, the SP units in pDSP-1 could be transformed into the protonated MC (MCH+) units after exposure to CF3COOH vapor, and the MCH+ moieties, in turn, could switch back to SP upon heating. For this reason, we investigated the variation of semiconducting performances of FETs- pDSP-1 after exposure to the vapor of CF3COOH and heating at 80 °C. First, BGBC FETs were treated with CF3COOH vapor at a concentration of 500 ppm for 1 min, followed by thermal treatment of the devices at 80 °C for 5 min. The transfer and output curves were measured separately before the treatments and after exposure to CF3COOH vapor and heating at 80 °C. As shown in Figure 3c,d, and , both transfer and output curves were varied after exposure to CF3COOH vapor, but the curves were almost restored after further thermal treatment. As listed in Table 1, the average device current (IDS) decreased from 6.5 × 10−5 to 2.3 × 10−5 A with a resultant current variation ratio [(I0−I)/I0] of 65%. After heating at 80 °C, the device current reincreased to 6.5 × 10−5 A. Such current variation could be repeated reversibly by alternating exposures to CF3COOH vapor and thermal treatment. Beside, for drain current, the variation of threshold voltages (Vths) was also observed, as shown in . For instance, Vth for the BGBC FET with pDSP-1 was varied from −5 to −3 V to −10 to −8 V after UV light irradiation. The reversible variation of the semiconducting performance was also observed by treatments with other acids, such as acetic acid (CH3COOH) and hydrochloric acid (HCl), followed by heating, as shown in . These results demonstrated that the semiconducting performances of FETs with pDSP-1 entailing SP units in the side chains could tune reversibly not only by alternating UV light irradiation, visible light irradiation or heating but also by treatment with CF3COOH vapor and heating. Notably, the transfer curves of FETs with pDSP-1 in which the SP units transformed into MC forms could be restored gradually after the devices were left in air for 2 h (see ). This also applied to FETs with pDSP-1 in which the SP units could convert into the MCH+ forms, as depicted in . These results could be attributable to both MC and MCH+ forms able to switch back to the SP forms at room temperature. Thus, the incorporation of SP units in the side chains of pDSP-1 enabled the semiconducting polymer to be multi-stimuli-responsive; accordingly, multi-stimuli-responsive FETs could be fabricated via coupling with such stimuli-responsive semiconducting polymer. Mechanism of FETs/pDSP-1 reversible modulation We further investigated the mechanism of the reversible modulation of the semiconducting performance of FETs with pDSP-1, which is associated with the reversible transformation among SP, MC, and MCH+ upon light irradiations, heating, and acid treatment. We first examined whether the transformation of SP units in pDSP-1 into MC units could influence the interchain packing, thin-film crystallinity, and morphology. We performed geometry measurements by grazing incidence wide-angle X-ray scattering (GIWAXS) on thin film of pDSP-1 untreated and external stimuli-treated samples. The GIWAXS patterns collected for thin film of pDSP-1 before and after UV light irradiation for 30 s and subsequent heating at 80 °C for 2 min are shown in . Our results showed that the 2D-GIWAXS patterns and the corresponding line-cut profiles of thin film of pDSP-1 after UV light irradiation and subsequent heating were almost the same as that of the untreated thin-film (). Both lamellar, including (100), (200), (300), and (400) peaks, and π–π stacking (010) signals for the pristine thin film of pDSP-1 were almost identical to those of the respective thin film after sequential treatments with UV light and heating (). shows the atomic force microscopy (AFM) height images for the untreated spin-coated thin film of pDSP-1 and those after UV light irradiation, followed by heating. The results also revealed no distinct differences in thin-film morphology, consistent with the root-mean-square roughness (RRMS), which remained unchanged for the thin film of pDSP-1 after treatments with UV light and heating. These studies demonstrated that thin-film crystallinity and were not by the transformation of SP units in pDSP-1 into the MC We also measured the of the pristine thin film of pDSP-1 and those after exposure to CF3COOH vapor and sequential thermal treatment at 80 °C (see ) and obtained similar the thin-film of pDSP-1 was also not further that its geometry was not by the treatments. the transformation of SP units in pDSP-1 into the MC units is associated with variations of the dipole moment, that the dipole moment of the SP form is whereas the MC form a dipole moment of In fact, as shown in Figure the for thin film of pDSP-1 were measured to be and before and after UV light irradiations, respectively. Such variation is consistent with the MC form a larger dipole moment than the SP form. is that the MCH+ form, achieved by treatment of the SP form with as the also possess a large dipole According to previous species such as MC and with large dipole might as charge carrier scattering sites by the which to decrease of the FETs device We also observed threshold voltage changes (), which might be due to the variations of charge or semiconducting and we could the reversible tuning of the semiconducting performances of FETs coupled with pDSP-1 to the dipole moment change among SP, MC or MCH+ forms, as in Figure Figure 4 | UV-vis absorption spectra the reversible of based on thin-film of pDSP-1 under UV light irradiation (365 nm for 30 s) and heating treatment (80 °C for 2 Download figure Download PowerPoint Figure 5 | mechanism for multi-stimuli-responsive FETs based on SP-containing semiconducting polymer. Download figure Download PowerPoint further that SP moieties of pDSP-1 are for the charge the polymer pDSP-5 of pDSP-1, Scheme in which the molar ratio of the SP-containing alkyl chains versus the branching ones is 1∶5, was prepared. Thus, polymer pDSP-5 contents of SP units than pDSP-1. After to we that the semiconducting performances of FETs coupled with pDSP-5 could also be tuned reversibly by light irradiations, and heating in the same as FETs with pDSP-1 (see ). However, as shown in Table 1, after UV light irradiation for 30 s, the average device current (IDS at VGS = VDS = −60 V) of pDSP-5 decreased to of the initial current. This further upon exposure of FETs coupled with pDSP-5 to UV and light irradiation, during which the current variation ratio to than that for the FETs device coupled with pDSP-1 under the same conditions. On the other the device current variation ratio exhibited similar after treatment with CF3COOH for FETs coupled with pDSP-5 and pDSP-1. Additionally, as shown in , the for thin film of pDSP-5 were measured to be and before and after UV light irradiations, respectively, and to be than the respective pDSP-1 (see Figure Thus, we from this comparative analysis because pDSP-5 a of SP units than pDSP-1, this resulted in the formation of of MC or MCH+ units after UV light irradiation or treatment with CF3COOH the charge within the thin film of pDSP-5 was by the UV light irradiation or treatment with CF3COOH vapor, with pDSP-1. We report a novel strategy for the of multi-stimuli-responsive polymeric semiconductors through the of SP groups in the side chains of a DPP-based D–A polymer by the of the reversible transformation of SP into MC or MCH+ under light irradiations, and heating. The semiconducting performances of FETs coupled with pDSP-1 that SP units could tune reversibly after alternating UV and visible light irradiations, alternating UV light irradiation, and heating, or alternating protonation with CF3COOH and heating. it was to fabricate multi-stimuli-responsive FETs with such semiconducting SP units in the side chains. Our current results that the molecular transformations among SP, MC, and MCH+ in the side chains of conjugated polymers could affect the charge within the semiconducting thin films. Accordingly, our studies new for applications of semiconducting is of are no

Cross-linked supramolecular polymers (CLSPs) are a special type of materials that combine the improved mechanical stability of covalently cross-linked network polymers with the dynamic and reversible interactions of supramolecular chemistry. In this review, the structures and characteristics of CLSPs are examined, with an emphasis on macrocycle-based architectures such as crown ethers, pillar[5]arenes, cryptands, cucurbiturils, calix[n]arenes, and calix[4]pyrroles. Among these macrocycles, calix[4]pyrrole-based CLSPs are important because they can interact with both neutral and anionic guest species, which endows them with unique binding characteristics, in contrast to other macrocycles that form complexes with cationic species. We focus on key examples from the recent literature, showing their crosslinking strategies and the properties of the resulting materials. We also emphasize the various applications of CLSPs in stimuli-responsive systems, self-healing materials, and biomedical applications. This review also highlights the potential of CLSPs as functional materials in the context of recent developments.

Three kinds of photoresponsive copolymers with azobenzene side chains were synthesized by radical polymerization of N‐4‐phenylazophenylacrylamide (PAPA) with N‐isopropylacrylamide (NIPAM), N,N‐diethylacrylamide (DEAM) or N,N‐dimethylacrylamide (DMAM) respectively. Their structures were characterized by FT‐IR, 1H‐NMR and UV/Vis spectroscopy. Their reversible photoresponses were studied with or without α‐cyclodextrin (α‐CD), which showed that both the copolymers and their inclusion complexes with α‐CD underwent rapid photoisomerization. The lower critical solution temperature (LCST) of the copolymers and their inclusion complexes with α‐CD were investigated by cloud point measurement, which showed that the LCST of three kinds of copolymers increased largely after adding α‐CD. After UV irradiation on the solutions of copolymers and their inclusion complexes, the LCST of the copolymers increased slightly with the absence of α‐CD, while decreased largely with the presence of α‐CD. Furthermore, the LCST reverted to its originality after visible light irradiation. This change of LCST could be reversibly controlled by UV and visible light irradiation alternately. In particular, in the copolymer of PAPA and DMAM, the reversible water solubility of the inclusion complexes could be triggered by alternating UV and visible light irradiation.

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In this study, the photocatalytic activity of annealed TiN powders and films were examined to clarify the influence of annealing temperature and pressure on the photocatalytic properties under UV and visible light irradiation. TiN films were deposited on stainless steel and quartz substrates by DC magnetron sputtering, and annealed TiN powders were used as a reference material to confirm the effectiveness of TiN oxidation. TiN powders which were annealed at 873-1173K, showed obvious photocatalytic activity, under both UV and visible light irradiation. However, annealed TiN films on the stainless steel substrate showed low photocatalytic activity except for those annealed at 823K and 1.0kPa. This is because film annealed above 923 K consisted of a dominant rutile phase, and the film annealed at 1023K delaminated from the stainless substrate. For the quartz substrate, the dominant phase of the films annealed at 823 and 923 K was anatase, and all films remained completely on the substrate after annealing. In particular, the film which was annealed at 923K and 1.0kPa showed high photocatalytic activity both under UV and visible light irradiation. Thus, good photocatalytic activity can be obtained by annealing TiN with an appropriate temperature, pressure and substrate material.

Three-dimensional multicellular spheroids are better in vitro cell models than two-dimensional cell monolayers; however, their applications are limited by their difficult production. PHEMA hydrogel films with honeycomb-like wrinkled patterns have been developed for high-throughput generation of multicellular spheroids with a uniform shape and size; however, the films are prepared by polymerization of the HEMA monomer, and should be washed extensively before use. Here to synthesize washing-free PHEMA hydrogel films, linear anthracene-functionalized PHEMA polymers were first synthesized by the free-radical copolymerization of HEMA and an anthracene-containing vinyl monomer. Smooth films were then prepared from the linear polymers in the wells of cell culture plates by solution casting. They were cross-linked via photo-dimerization of anthracene groups by exposing to 365 nm UV light, and patterned spontaneously by adding water to swell them. The swelling degree of the films and hence the shape of the wrinkled patterns could be facilely adjusted by adjusting the anthracene content in the linear polymers. If necessary, the cross-link density of the film and thus the shape of the wrinkled patterns could be callbacked by irradiating with 254 nm UV light, thanks to the reversibility of the photo-dimerization of anthracene. The as-prepared films exhibit a high biocompatibility and support cell growth well even without washing and sterilization. The high biocompatibility is attributed to the facts that no low molecular weight monomer, crosslinker and initiator were involved in the film preparation, and the photo-dimerization of anthracene groups produces no by-products. The films are sterilized simultaneously when cross-linked with UV irradiation, thus avoiding an additional sterilization step. PHEMA films with long-range ordered hexagonal wrinkled patterns were selected to generate multicellular spheroids of tumor cell lines. The resulting spheroids exhibit a narrow size distribution and high cell viability. Preliminary tests demonstrated their potential in the screening of anti-cancer drugs.

The photocatalytic activity of iron-containing metal-ceramic composites based on silicon nitride modified with semiconductor tantalum oxo compounds in the process of oxidative degradation of diclofenac (DCF) was investigated. The composites were synthesized by autowave combustion in nitrogen atmosphere of ferrosilicoaluminum with different additives (5, 10, 15 wt%) of metallic tantalum. The phase composition was determined by X-ray diffraction and IR-spectroscopy, and the content of elements in local surface areas was quantitatively evaluated by X-ray spectral microanalysis. The activity of composites under conditions of heterogeneous photocatalysis, combined heterogeneous photocatalysis with photo-Fenton and "Peroxone" processes under UV irradiation, catalytic ozonation under UV and visible light irradiation was studied. The combination of heterogeneous photocatalysis and "Peroxone" process is the most effective. The Langmuir-Hinshelwood scheme was applied to establish the mechanism of DCF photocatalytic degradation process.

Problem statement: Since bacteria mainly causes damage on fresh vegetables and fruits during transportation to market, anti-bacterial TiO2 photocatalyst was applied for their packaging films. However, it has been known that pure TiO2 exhibits low photocatalytic property due to rapid recombination of photo-activated electrons and holes. Doping with metal or metal oxide shows the improvement of photocatalytic activity and disinfection effect. Approach: Fe3+ was considered to dope into TiO2/3SnO2 photocatalyst in order to enhance the photocatalytic property and bacterial inactivation efficiency. The Fe3+ doped TiO2/3SnO2 nanoparticles were prepared by sol-gel method and calcined at 400 °C for 2 h. The synthesized powders were characterized by XRD, BET and SEM. Photocatalytic activity and bacteria killing effect were determined by means of degradation of methylene blue solution and inactivation of E. coli bacteria, respectively. These tests were performed under UV and visible light irradiations. Results: Fe3+ doping into TiO2/3SnO2 has an effect on inhibition of anatase crystal growth, led to the enlargement of the composite specific surface area. Therefore, the photocatalytic activity of Fe3+ doped TiO2/3SnO2 composite in proper concentration was greater than those of pure TiO2 and TiO2/3SnO2 and 0.5 mol% Fe3+ doping exhibited the highest photocatalytic activity and E.coli inactivation efficiency. The E. coli was completely killed within 90 min under UV irradiation or 99.7% inactivated under visible light exposure. Conclusion: Fe3+ doped TiO2/3SnO2 nanoparticles were successfully synthesized and identified as 100% anatase phase. The 0.5mol% Fe3+-doped TiO2/3SnO2 which has particle size of 12.89 μm and specific surface area of 117.61 m2 g-1, exhibited the highest activity and disinfection efficiency. An attractive feature of Fe3+ doped TiO2/3SnO2 photocatalytic disinfection is its potential to be activated by visible light. Therefore, these composite TiO2 nanoparticles can be utilized for fresh food packaging films.

Photoresponsive polymer with azobenzene pendant group (PDMAA‐co‐PAPA) was synthesized by radical polymerization of N,N‐dimethylacrylamide (DMAA) and N‐4‐phenylazophenyl acrylamide (PAPA), and the characterization of the inclusion complexes of the PDMAA‐co‐PAPA with α‐cyclodextrin (α‐CD) were performed by FTIR, GPC, 1H NMR, 2D NOESY, and UV–vis spectroscopy. It was found that the solubility of PDMAA‐co‐PAPA and α‐CD inclusion complexes in aqueous solution showed tunable property, which could be triggered by alternating UV–vis light irradiation at a certain temperature due to the effect of molecular recognition of α‐CD with azobenzene moiety in the polymer. After UV irradiation, the lower critical solution temperature (LCST) of the polymer aqueous solution increased slightly without α‐CD while the LCST decreased sharply at presence of α‐CD. Furthermore, UV spectroscopy showed that the photoisomerization of the polymer solution went on rapidly and reversibly, and 2D NOESY data suggested that the inclusion complexation of α‐CD with trans azobenzene moiety and the decomplexation with cis azobenzene resulted in reversible solubility behavior when objected to UV and Vis light irradiation alternately. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Liquid–liquid equilibria in ternary systems of linear and cross-linked water-soluble polymers