Photo-induced Alignment Behavior of Azobenzene-containing Polymer Films with Different Cross-linking Degree

Three series of amorphous copolymers containing azobenzene groups with various substituents and certain amounts of crosslinkable acrylic groups were prepared. The cross-linked polymer films were obtained by thermal polymerization of the acrylic groups in the copolymers, during which, by controlling the time of cross-linking reaction, the films can be made with different cross-linking degree （from 0 to 32%, which was monitored by FT-IR spectra measurement）. Photo-induced alignment process of the films was performed under irradiation with linearly polarized light at 442 nm, and the effect of cross-linking degree on the photo-induced alignment rate was investigated. The dynamics of the photo-induced alignment was analyzed with biexponential curve fitting. The photo-induced alignment rate and the maximum transmittance of the films decreased because of the cross-linking. Furthermore, for the cross-linked samples, it was found that their saturated value of transmittances keep constant after repeated ＂writing＂ and ＂erasing＂ cycles. The findings reveal that the cross-linking of the film can effectively restrain the phototactic mass transport of azopolymer during irradiation by polarized light. The relationship between the cross-linking degree and the photo-induced alignment behavior of azopolymer is discussed in detail.

Photo-induced intramolecular electron transfer and intramolecular vibrational relaxation of rhodamine 6G in DMSO revealed by multiplex transient grating spectroscopy

Photo-induced intramolecular electron transfer （PIET） and intramolecular vibrational relaxation （IVR） dynamics of the excited state of rhodamine 6G （Rh6G＋） in DMSO are investigated by multiplex transient grating. Two major compo- nents are resolved in the dynamics of Rh6G＋. The first component, with a lifetime τTPIET = 140 fs-260 fs, is attributed to PIET from the phenyl ring to the xanthene plane. The IVR process occurring in the range ZIVR = 3.3 ps-5.2 ps is much slower than the first component. The PIET and IVR processes occurring in the excited state of Rh6G＋ are quantitatively determined, and a better understanding of the relationship between these processes is obtained.

PHOTO-INDUCED DOPED POLYANILINE BY THE VINYLIDENE CHLORIDE AND METHYL ACRYLATE COPOLYMER AS PHOTO ACID GENERATOR

The emeraldine base form of polyaniline (PANI) can be doped by a photo-induced doping method. In this method a. copolymer of vinylidene chloride and methyl acrylate (VCMAC) was used as photo acid generator which can release proton when it is exposed to ultraviolet light (lambda = 254 nm). The structure of PANI-VCMAC system before and after irradiation was characterized by elemental analysis, IR, XTP, anti SEM images. Results obtained indicate that the photo-induced doping characteristics, such as doping position and type of charge carriers, are similar to that of PANI doped with HCl. The poor room-temperature conductivity (similar to 10-S-5/cm) of PANI-VCMAC system after irradiation may be due to low doping degree (similar to pH=3) and the difference in morphology as compared with PANI-HCl film.

Photo-induced Phenomena in GeS_4 Glasses

GeS4 bulk glasses were prepared by the melt-quench technique and the samples were irradiated by 532-nm linearly polarized light. After the laser treatment, the photo-induced changes of the samples were investigated by UV-1601 speetrophotometer and optical second-order nonlinear tester. The results show that the transmittance of the samples around 532 nm obviously decreases and Bragg reflector forms, which is due to the production of photon-generated carriers. With the increase of laser pulse energy or the extension of irradiation duration, the Bragg reflector increases and gradually tends to be stable. These can be ascribed to the excitation- capture process of the carriers. After irradiation, the relaxation phenomenon results from the release of part of the absorbed energy in the glass matrix. And the fitting equation of the relaxation process is consistent with a conventional Kohlrausch stretched exponential function. The origin of the second harmonic generation （SHG） is because of the dipole reorientation caused by the photo-induced anisotropy in the glass.

STUDY ON PHOTO-INDUCED ORIENTATION OF A NOVEL PHOTO-ALIGNMENT FILM WITH SURFACE ENHANCED RAMAN SCATTERING (SERS) SPECTROSCOPY

Surface enhanced Raman scattering (SERS) spectroscopy was first utilized to study the photo-orientation behaviour of the photoreactive groups on a novel photo-alignment film surface and elucidate the generation mechanism of pretilt angle. The novel photo-alignment film was prepared by spin-coating a solution of ladderlike polysiloxane (LPS) bearing dual photoreactive group on an ITO surface and by irradiation with linear-polarized ultraviolet (LPUV) light A Si—H terminal compound (M) containing an identical photosensitive part has been used to fabricate a model film for SERS investigation.

Photo-induced Coupling Reaction of 1,1-Diphenyl-2,2-dicyanoethylene with 10-Methyl-9,10-dihydroacridine

Diphenyl-2, 2-dicyanoethylene reacts with 10-methyl-9, 10-dihydroacridine in deaerated acetonitrile under irradiation with l>320 nm to give the coupling product 1, 1-diphenyl-1-(10-methyl-9-acridinyl)-2, 2-dicyanoethane, which has been characterized by X-ray crystallographic, MS and NMR analyses.

Photo-induced absorption in the pump probe spectroscopy of single-walled carbon nanotubes

Femtosecond pump probe spectroscopy is employed to study the photo-induced absorption feature in the single-walled carbon nanotube transient spectrum. The two advantages of the experiment, a chirality enriched sample and tuning the pump wavelength to the resonance of a specific nanotube species, greatly facilitate the identification of the photo-induced absorption signal of one tube species. It is found that a photo-induced absorption feature is located at one radial breathing mode to the blue side of the E11 state. This finding prompts a new explanation for the origin of the photo-induced absorption： the transition from the ground state to a phonon coupled state near the E ii state. The explanation suggests a superposition mechanism of the photo-bleach and photo-induced absorption signals, which may serve as a key to the interpretation of the complex pump probe transient spectrum of carbon nanotubes. The finding sheds some light on the understanding of the complex non-radiative relaxation process and the electronic structure of single-walled carbon nanotubes.

Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCI molecule encapsulated in C60 under femtosecond laser pulses

By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level.

CHARGE-TRANSFER AND ENERGY-TRANSFER IN THE PHOTO-INDUCED COPOLYMERIZATION OF 2-VINYLNAPHTHALENE WITH MALEIC ANHYDRIDE

The initiation mechanism of the copolymerization of 2-vinylnaphthalene with maleic anhydride was studied under irradiation of 365 nm. The excited complex was formed from (1) the local excitation of 2-vinylnaphthalene followed by the charge-transfer interaction with maleic anhydride and (2) the excitation of the ground state charge-transfer complex, and then it collapsed to 1,4-tetramethylene biradical for initiation. A1: 1 alternating copolymer was formed in different monomer feeds. Addition of benzophenone could greatly enhance the rate of copolymerization through energy-transfer mechanism.

Photo-Induced Thermally Stimulated Depolarization Current (TSDC) in Natural and Synthetic Alexandrite (BeAl2O4:Cr3+)

The investigation of electrical properties in alexandrite (BeAl2O4:Cr3+) in synthetic and natural forms is presented in this paper. Alexandrite is a rare and precious mineral that changes color according to the light incident on it. In the synthetic form, it is used technologically as an active laser medium. The electrical characterization was obtained using the Thermally Stimulated Depolarization Current (TSDC) technique, an interesting tool to study the behavior of impurities in insulators. Alexandrite presented the electric dipole relaxation phenomenon, both in natural and in synthetic samples. It was possible to observe TSDC bands for the synthetic sample at around 170 K, and at around 175 K for the natural sample. Besides, photo-induced TSDC measurements were performed through the excitement of the samples by using a continuous wave argon laser. In addition, photoluminescence measurements were performed to verify in advance whether the laser light would be absorbed by the sample, and in order to complement the photo-induced TSDC measurements analysis. The results of photo-induced TSDC experiments have contributed to the understanding of the TSDC bands behavior: the results obtained with the technique suggest that there is an effective participation of Cr3+ ions in the formation of TSDC bands because they were more intense when the sample was exposed to the argon laser beam.

Photo-induced Ag modulating carbon dots:Greatly improved fluorescent properties and derived sensing application

Carbon dots(CDs)have been attracted much attention and widely studied due to their excellent fluorescence(FL)properties,better biocompatibility and outstanding photo/chemical stability.However,the disadvantage of lower quantum yield(QY)still limits its wide application.Herein,we reported a novel and convenient strategy to prepare photo-induced Ag/CDs(p-Ag/CDs)by irradiating the mixed Ag+and hydrophobic CDs(h-CDs)acetone solution with ultraviolet(UV)light.The obtained p-Ag/CDs exhibit a greatly enhanced FL emission together with a blue shift(460 nm)than h-CDs(520 nm).The QY of p-Ag/CDs is measured to be 51.1%,which is 10.4 times higher than that of h-CDs(4.9%),indicating that photo-induced Ag modulation can effectively improve the optical properties of CDs.The mechanisms for the FL enhancement and blue shift of h-CDs are studied in detail.The results prove that the greatly enhanced FL emission is from the generated Ag nanoparticles(AgNPs)by UV light irradiation based on metal-enhanced fluorescence(MEF),and the increased oxygen-contained groups in this process lead to the blue shift in CDs fluorescence.Interestingly,the p-Ag/CDs exhibit higher sensitivity and selectivity for sulfide ions(S2-)detection than that of h-CDs,which have a lower response to S2-.This work not only offers a novel strategy to improve the FL properties of materials but also endows them with new functions and broadens their application fields.

Photo-induced grease/oil switched lubricant for friction regulation

Controllable friction regulation has drawn much interest in both scientific and industrial fields.And there have been many researches on friction regulation by many physical fields and chemical factors.Photo-sensitive materials are promising because it is relatively easy to change their properties compared with others.Here,a new kind of photo-induced grease/oil switched lubricant is designed and shows great reversibility under ultraviolet(UV)and visible(Vis)irradiation.Its viscosity can change more than 50 times under different irradiation,and the coefficients of friction(COFs)obviously increase under Vis irradiation and decrease under UV irradiation,which performs better than those of the common grease.According to the experimental results,the phenomena are contributed to the break and reconstruction of the three-dimensional network inside the lubricant.With a switchable grease/oil state under different irradiation,this work provides a new principle for designing a smart lubricant with controllable friction regulation.

Investigation on the photo-induced de-oxygenation process of myoglobin in aqueous solution by use of fluorescence spectroscopy

A photo-induced de-oxygenation process of myoglobin (Mb) in aqueous solution was investigated by use of fluorescence spectroscopy. The spectra are characterized by the fluorescence intensity declining gradually after each scan,and the decay of fluorescence intensity being significant in each scan,which is assigned to the release of oxygen from the opening of the heme-pockets induced by illumination. More illumination will cause more release of oxygen; if the temperature of an Mb solution is increased when it is illuminated,the rate of de-oxygenation will be higher. It was found that ligand-oxygen in Fe-porphyrin could be removed from Mb by nitrogen. This indicates that the interac-tion between oxy-Mb and other different gases can be tested by the method of fluorescence spectros-copy. In addition,fluorescence spectroscopy can be employed to probe the energy transfer between Fe-porphyrin and tryptophan or tyrosine in Mb molecules.

Photo-induced visual response of western flower thrips attracted and repulsed by their phobotaxis spectrum light

This study aimed to clarify the synergistic phototactic attraction-repulsion effect formed by the photo-induced approach-avoidance behavior of thrips,construct phototactic attraction-repulsion light control technologies.The phototactic push-pull effects of red light and UV(365 nm),violet(405 nm),green(520 nm),and yellow(560 nm)single light,as well as their pairwise combined light on the behavior of western flower thrips were investigated using an apparatus that measured thrips response.The study also analyzed the influence of light properties on the phototactic attraction-repulsion effects of thrips and the synergistic effects of red light,and the attraction-repulsion regulation mode.The influence factors on the photo-induced attraction-repulsion effect of thrips were also discussed.The results showed that the red light,presenting the push effect,drove thrips to respond to the sensitive light.The synergistic attraction-repulsion effect of red light and singlelight,as well as that of red light and combined light was related to the light intensity.However,the attraction-repulsion synergism did not reflect thrips response effect and approach effect pulled and pushed by red light and single light,red light and combined light.Thrips preference for green-yellow light,and their behavior depended on the degree of UV light,making the attraction-repulsion synergy of red and green light the strongest.When the light intensity increased,the attraction-repulsion synergy of red and yellow light was the strongest.The attraction-repulsion response to red light and single light was related to the spectral attribute of the single light,with that of red lightand UV light being better.The attraction-repulsion response to red light and combined light was related to light intensity.The intensity of combined light made the attraction-repulsion response to red light and the combined UV and violet light be the best,and the brightness of long-short spectrum light rendered red light and the combined UV and yellow light the best.All such light and combinations were remarkably better than that of red light and UV light.Relative to red light and UV light,the use ofred light and combined light provided limited enhancement to the approach effect of thrips;however,under red light and combined light,violet light intensified the approach of thrips to UV light,with yellow light strengthening the approach to green light.Those results provided a scientific basis for the development of light trapping equipment and the adjustment of light control strategies for thrips.

Photo-induced effect in the layered perovskite manganite La_(1.2)Sr_(1.8)Mn_(1.8)Co_(0.2)O_(7)

It is helpful to study the photo-induced effect in the perovskite manganites not only for elucidating the mechanism of colossal magnetoresistance (CMR) effect but also for potential applications in technology. The laser-induced effect in the Co doping layered perovskite manganites La1.2Sr1.8Mn1.8Co0.2O7 is studied in this paper and the obtained results are also compared with that gained in the Nd-doping manganites with cubic perovskite structure.

A Novel Method for Measuring Photo-Induced Birefringence of Photosensitive Fibers

In this paper, we report a novel method for accurately measuring the photo-induced birefringence of photosensitive fiber by using Mach-Zehnder interferometer. The results indicate that the normalized birefringence can attain 10-5.

Stabilizing photo-induced vacancy defects in MOF matrix for highperformance SERS detection

Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering(SERS)sensing,photocatalysis,and photovoltaic applications.However,the long-term maintenance and use of photo-induced vacancy defects remain elusive,because of their rapid self-healing upon air exposure.In this study,we demonstrate that photo-induced oxygen vacancy(PIVO)defects can be stabilized by the photoexcitation of metal–organic framework(MOF)materials,which is crucial for SERS analysis.The PIVO defects in MOF materials are stable for at least two weeks in the ambient atmosphere,owing to the combination of steric hindrance and electron delocalization around vacancy defects,which significantly contrasts the short lifetime(within minutes)of PIVO defects in metal-oxide semiconductors.With the formation of stable PIVO defects,a prominent SERS enhancement surpassing that of pristine MOFs is achieved,accompanied with a reduced limit of detection by three orders of magnitude.Moreover,the additional SERS enhancement rendered by PIVO defects can be stably retained and is effective for monitoring various small molecules,such as dopamine and bisphenol A.

Photo-induced deep aerobic oxidation of alkyl aromatics

Oxidation is a major chemical process to produce oxygenated chemicals in both nature and the chemical industry.Presently,the industrial manufacture of benzoic acids and benzene polycarboxylic acids(BPCAs)is mainly based on the deep oxidation of polyalkyl benzene,which is somewhat suffering from environmental and economical disadvantage due to the formation of ozone-depleting Me Br and corrosion hazards of production equipment.In this report,photo-induced deep aerobic oxidation of(poly)alkyl benzene to benzene(poly)carboxylic acids was developed.CeCl_(3) was proved to be an efficient HAT(hydrogen atom transfer)catalyst in the presence of alcohol as both hydrogen and electron shuttle.Dioxygen(O_(2))was found as a sole terminal oxidant.In most cases,pure products were easily isolated by simple filtration,implying large-scale implementation advantages.The reaction provides an ideal protocol to produce valuable fine chemicals from naturally abundant petroleum feedstocks.

PHOTO-INDUCED INTERMOLECULAR AND INTRAMOLECULAR ELECTRON-TRANSFER REACTIONS BETWEEN XANTHENE DYES AND DONORS/ACCEPTORS

A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced electron transfer reactions were determined and calculated. It is found that the photo-induced electron transfer reactions occurred between xanthene dyes and many, including very weak donors or acceptors. The rate constants of intermolecular reactions were controlled by diffusion, and influenced by the reactant concentrations. The laser flash experiments showed that for low reactant concentrations, this kind of reactions took place mainly via the triplet excited state of the dyes. If different electric charges exist with dyes and donors/acceptors, there will be static quenching of the dyes’ fluorescence. The intramolecular electron transfer reactions are independent of the solution concentrations, and they may directly proceed via the singlet excited state of the dyes effectively.

Contributions of Cs and Rb on Inhibiting Photo-induced Phase Segregation and En-hancement Optoelectronic Performances of MA_(1-y)XyPbI_(1.8)Br_(1.2)(X=Cs,Rb)Single Crystals

Introducing inorganic cation into hybrid organic-inorganic perovskites(HOIPs)has attracted great attention because of the enhancement stabilities without sacrificing their excellent optoelectronic properties.Here,we introduce Cs and Rb into MAPbI_(1.8)Br_(1.2)single crystals(SCs)to dig out the mixed cation effect on optoelectronic performances and phase stabilities.Both Rb and Cs can increase the lattice capacity,which is sufficient to relieve the lattice stress caused by photon energy,thus achieving the purpose of stabilizing the lattice structure and inhibiting migration of halide ions,compared with MAPbI_(1.8)Br_(1.2)SC.On the other hand,the smaller polarity of Rb and Cs reduces the electron-phonon coupling,thus significantly inhibiting the migration of halide ions.Meanwhile,through planar photo-detectors,MA_(0.9)Cs_(0.1)PbI_(1.8)Br_(1.2)-based device behaves much excellent optoelectronic performance(R=0.170 A/W,EQE=51.39%,D^(*)=4.42×10^(12)Jones,on/off ratio:~522).