Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide

This paper studies the intramolecular photoinduced electron-transfer （PET） of covalent bonded azobenzene-perylene diimide （AZO-PDI） in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 10^11 s^-1 is found. This PET process is also consolidated by femtosecond transient absorption spectra.

Light-Responsive Proton Conductor:Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Light-responsive proton conductors might find applications in both traditional fields(fuel cells,chemical sensors,bio-ionic functions,etc.)and modern high-speed switchable smart systems(Internet of things,robotics,etc.).Previous synthetic methods resulted in low switching contrasts(<two times)or they tended to be limited significantly in solid matrixes due to large structural changes.The photoinduced electron-transfer(PIET)method avoids the influence of stereo space in solid matrixes and capable of achieving high switching contrasts.For the first time,we applied the PIET strategy to design lightresponsive proton conductors to achieve the hitherto largest gain of proton conductivity(ca.54 times)for light-responsive proton conductors in one crystalline photochromic viologen-based H-bonded supramolecule.The weakening of hydrogen-bonding interactions in the proton-transport path after PIET accounted for an increased proton conductivity.These findings would inspire the exploration of photon conductors that display higher proton conductivities or switchable smart systems with high contrasts.

Photoinduced phase segregation in wide-bandgap mixed-halide perovskite solar cells

Wide-bandgap(WB)mixed-halide perovskite solar cells(PSCs)play a crucial role in perovskite-based tandem solar cells(TSCs),enabling them to exceed the Shockley-Queisser limits of single-junction solar cells.Nonetheless,the lack of stability in WB perovskite films due to photoinduced phase segregation undermines the stability of WB PSCs and their TSCs,thus impeding the commercialization of perovskite-based TSCs.Many efforts have been made to suppress photoinduced phase segregation in WB perovskite films and significant progresses have been obtained.In this review,we elaborate the mechanisms behind photoinduced phase segregation and its impact on the photovoltaic performance and stability of devices.The importance role of advanced characterization techniques in confirming the photoinduced phase segregation are comprehensively summarized.Beyond that,the effective strategies to alleviate photoinduced phase segregation in WB mixed halide PSCs are systematically assessed.Finally,the prospects for developing highly efficient and stable WB PSCs in tandem application are also presented.

PHOTOINDUCED BIREFRINGENCE AND NUMERICAL SOLUTION OF A NEW DYNAMIC MODEL IN AN AMORPHOUS COPOLYMER CONTAINING AZOBENZENE GROUPS

Photoinduced birefringence is investigated in a new amorphous copolymer containing azobenzene groups. The levels of birefringence signal are found to depend an the polarization angle between the pump beam and the probe beam, and on the ellipticity of the pump beam. Both the growth and decay processes of the birefringence signal can be described by known biexponential equations. The rate constants and the amplitudes associated with the growth process of the photoinduced birefringence are observed to display a linear dependence with the pump beam intensity. A new dynamic model of the photoinduced birefringence is presented taking into account the contributions of both the bans and cis isomers of azobenzene groups and the local polymer segments. The numerical treatment of this model shows good agreement with the experimental data in the whole writing-erasing processes of the photoinduced birefringence conducted in our polymer samples.

Ni nanoparticles as electron-transfer mediators and NiS_x as interfacial active sites for coordinative enhancement of H_2-evolution performance of TiO_2

The development of efficient photocatalytic H2-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H2 production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron- transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H2-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H2 by Ni-modified TiO2, the formation of NiSx as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO2/Ni-NiSx photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO2 surface and the subsequent formation of NiSx on the Ni surface by a hydrothermal reaction method. It was found that the TiO2/Ni-NiSx photocatalysts exhibited enhanced photocatalytic H2-evolution activity. In particular, TiO2/Ni-NiSx(30%) showed the highest photocatalytic rate (223.74 μmol h.1), which was greater than those of TiO2, TiO2/Ni, and TiO2/NiSx by factors of 22.2, 8.0, and 2.2, respectively. The improved H2-evolution performance of TiO2/Ni-NiSx could be attributed to the excellent synergistic effect of Ni and NiSx, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO2 surface and NiSx serves as interfacial active sites to capture H+ ions from solution and promote the interfacial H2-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.

A silica-immobilized Pt^(2+) catalyst for the selective,aerobic oxidation of methane via an electron-transfer chain

The combination of Pt^2＋, benzoquinone and NaNO2 forms an electron-transfer chain, which leads to the oxidation of methane by O2 in CF3COOH aqueous solution. The overall turnover number per hour （TOF） of methane at 120 ℃ is 0.5 h^-1, however, only about one fourth （23%） of methane is converted to the desired product of methanol in the formation of CF3COOCH3. The over-oxidation of methane to CO2, over the catalyst with the Pt^2＋ species immobilized via 2,2＇-bipyridyl as a ligand on the silica substrate, is depressed distinctly. Under the same conditions, the conversion to methanol dominates, and no CO2 is observed, on account of the over-oxidation of methane, as confirmed by the isotope experiment.

Effects of Lycium barbarum polysaccharide on the photoinduced autophagy of retinal pigment epithelium cells

AIM:To investigate the relationship between autophagy and apoptosis in photoinduced injuries in retinal pigment epithelium(RPE)cells and how Lycium barbarum polysaccharide(LBP)contributes to the increased of RPE cells to photoinduced autophagy.METHODS:In vitro cultures of human RPE strains(ARPE-19)were prepared and randomly divided into the blank control,model,low-dose LBP,middle-dose LBP,high-dose LBP,and 3-methyladenine(3MA)groups.The viability of the RPE cells and apoptosis levels in each group were tested through cell counting kit-8(CCK8)method with a flow cytometer(Annexin V/PI double staining technique).The expression levels of LC3II,LC3I,and P62 proteins were detected with the immunofluorescence method.The expression levels of beclin1,LC3,P62,PI3K,P-mTOR,mTOR,P-Akt,and Akt proteins were tested through Western blot.RESULTS:LBP considerably strengthens cell viability and inhibits the apoptosis of RPE cells after photoinduction.The PI3K/Akt/mTOR signal pathway is activated because of the upregulation of the phosphorylation levels of Akt and mTOR proteins,and thus autophagy is inhibited.CONCLUSION:LBP can inhibit the excessive autophagy in RPE cells by activating the PI3K/Akt/mTOR signaling pathways and thereby protect RPE cells from photoinduced injuries.

Studies on the Technology and Mechanism of Laser Photoinduced Alignment of Liquid Crystal

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Study of Photoinduced Interaction between Calf Thymus-DNA and Bovine Serum Albumin Protein with H₂Ti₃O₇Nanotubes

Hydrogen titanate nanotubes were synthesized by hydrothermal process using 10 M NaOH and TiO2 anatase powder. The material synthesized was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to ensure the structural and morphological characteristics. The interaction of calf thymus DNA (CT-DNA) and bovine serum albumin protein with suspended aqueous solution of titanate nanotubes was investigated using UV absorption spectroscopy and the apparent association constant was found to be, Kb= 1.68 × 104 M-1 and Kap=5.41 × 103 M-1 for DNA and BSA respectively. Addition of the titanate nano material resulted quenching of fluorescence spectra of ethidium bromide-DNA in tris HCl buffer solution and that of aqueous protein solution. The apparent binding constant (Ksv= 5.46 × 104M-1 for DNA binding and Ksv = 6.063 × 103M-1 for protein binding) was deduced from relevant fluorescence quenching data using Stern-Volmer equation.

PHOTOINDUCED ADDITION REACTIONS OF CHLORANIL WITH FURAN DERIVATIVES

Photoinduoed reaction of chloranil (TCBQ) with 2-methylfuran la and 2,5-dimethylfuran 1b in benzene gave addition products 2a and 2b respecvely together with tetrachlorohydroquinone 3. A mechanism of sequential electron and proton transfer from la or 1b to ~3TCBQ followed by coupling of the furfuryl and semiquinone radical pairs was proposed and is evidenced by the photo-CIDNP studies of the TCBQ-1a and TCBQ-1b systems.

Physical Diffusion and Electron-transfer Dynamics of Electroactive Solutes in Polymer Electrolytes Ⅲ. Effect of the Polymer Solvents

The diffusion coefficients(Dapp) and the heterogeneous electron transfer rate constants(ks)for ferrocene in several polymer solvents were determined by using steady-stae voltammetry. Thetemperature dependence of the two parameters indicates Arrhenius behavior. The polymer solventeffects on diffusion and electron transfer dynamics of ferrocene were discussed

Photoinduced Second Harmonic Generation of Bi_2S_3 Microcrystallite Doped Silica Glass

Silica glasses doped with Bi2S3 microcystallite was prepared by the sol-gel process. Photoinduced second harmonic generation (SHG) was observed in the glass when it was irradiated with intense 1.06 mum and frequency doubled laser beams from a mode-locked Nd: YAG laser. It was found that the signal intensity increased with the irradiating time and approached a saturation gradually. The effect may be explained reasonably by the DC field model.

PHOTOINDUCED S_(RN)1 REACTIONS OF ARYL HALIDES WITH CARBAZOLYL NITROGEN ANION

The photoinduced reactions of aryl halides with carbazolyl nitrogen anion,in dimethyl sulfoxide,yield the corresponding N-arylated products.These reactions are suggested in terms of the S;Nl mechaism of nucleophilic substitution.

Review of photoinduced effect in manganite films and their heterostructures

Light–matter interaction plays an important role in the non-equilibrium physics, especially in strongly correlated electron systems with complex phases. Photoinduced effect can cause the variation in the physical properties and produce some emergent phases. As a classical archetype, manganites have received much attention due to their colossal magnetoresistance（CMR） effect and the strong interaction of charge, spin, orbital, and lattice degrees of freedom. In this paper, we give an overview of photoinduced effect in manganites and their heterostructures. In particular, some materials, including ZnO, Si,BiFeO3（BFO）, titanate-based oxides, and 0.7 Pb（Mg（1/3） Nb（2/3））O3-0.3 PbTiO3（PMN-PT） have been integrated with manganites. Heterostructures composed of these materials display some exciting and intriguing properties. We do hope that this review offers a guiding idea and more meaningful physical phenomena will be discovered in active areas of solid state physics and materials science.

Photoinduced Electron Transfer in Host-Guest Complexes of Naphthalene Derivatives with p-NBCD and m-NBCD

A number of naphthalene derivatives containing adamantanamine binding moiety and an （CH2）. （n = 2, 3, 4, 5, 6） spacer were prepared as electron donor. A supramolecular assembly was fabricated by the inclusion complexation of the donor substrates with the host molecules, mono-6-O-p-nitrobenzoyl-β-cyclodextrin （p-NBCD） and mono-6-O-m-nitrobenzoyl-β-cyclodextrin （m-NBCD）, in water. The fluorescence quenching in these systems was studied and detailed Stern-Volmer constants were measured. It revealed that an efficient photoinduced electron transfers （PET） between the naphthalene donors and the cyclodextrin acceptors occurred.

Photoinduced DNA Cleavage of Fullerols,Water-Soluble Polyhydroxylated [C_(60)] Fullerene Derivatives

The effects of polyhydroxylated [C60 ] fullerene derivatives fullerols on DNA was studied, using the piasmid pXJ41-neo DNA as the experimental model. The cleaved DNA products were detected by agarose gel electrophoresis. The results showed that fullerols could stimulate DNA cleavage in dose and irradiation dependent manners. 0.4 mmol/L fullerols together with 1.5 h exposure to a 500 W tungsten halogen lamp at a distance of 20 cm could convert most of plasmid DNA from the intact form into the nicked and linear forms. Scavengers of various reactive oxygen species （ROS） including sodium azide, mannitol and superoxide dismu- tase （SOD） could inhibit the photoinduced DNA cleavage of fuUerols. These data presented for the first time the photoinduced biological activities of fullerols, and implied a possible use of these fullerene derivatives as the candidates for novel photosensitizers in the biomedical therapy.

PHOTOINDUCED CHARGE TRANSFER POLYMERIZATION OF STYRENE INITIATED BY ELECTRON ACCEPTOR

Photoinduced charge transfer polymerization of styrene(St) with electron acceptor as initiator was investigated. In case of fumaronitrile (FN) or maleic anhydride (MA) as initiator the polymerization takes place regularly, whereas the tetrachloro-1,4-benzenequinone (TCQ), 2,3-dichloro-5, 6-dicyano-1, 4-benzenequinone (DDQ). or tetracyano ethylene (TCNE) as initiator the polymerization proceeds reluctantly only after the photoaddition reaction. A mechanism was proposed that free radicals would be formed following the charge and proton transfer in the exciplex formed between St and electron accepters.

Photoinduced Electron Transfer (PET) between C_(60) and Amines in Micelle Solution A Kinetic ESR Study

As indicated by kinetic ESR measurements, the key factor to affect electron recombination in the process of PET between C60 and amines is the space between donor and C60. To increase solubility of C60 in water, it was incorporated into micelle of surfactants. ]

KINETICS AND MECHANISM OF PHOTOINDUCED POLYMERIZATION BY α,α-DIMETHOXY-α-PHENYL ACETOPHENONE

α,α-dimethoxy-α-Phenyl acetophenone (DMPA) is an efficient and thermally stable photoinitiator. Here its spectral characteristics in the transient state were shown. The transient species were identified as a benzoyl radical and a dimethoxyi benzyl radical that played a primary initiation role in polymerization. The kinetics and mechanism of the bulk polymerization of MMA were investigated. The exponent of DMPA concentration and k_p/k_1^(1/2) value were found to be 0.5 and 0.066 mol(-1/2)l^(1/2)s^(-1/2), respectively. The existence of oxygen led to obtain the polymer with higher molecular weight, which can be attributed to the occurrence of the subsequent polymerization induced by active polymer end group. In the photocrosslinking reaction, the dependence of DMPA content on initial rate has been found. A principal reason is that the sample contained higher percentage of DMPA has higher light-absorbed efficiency. In solid film, higher concentration of DMPA is permitted to be used because there is little excited state self-quenching effect in the rigid medium.

PHOTOINDUCED ALIGNMENT OF OPTICALLY ACTIVE POLYMER CONTAINING A TEMPO RADICAL END GROUP

A new azobenzene side-chain polymer (TEMPO-PAZ) containing TEMPO (4-hydroxy-2, 2, 6, 6-tetramethyl-piperidinooxy) radical end group was synthesized by free radical copolymerization. Photoinduced alignment was studied onthe polymer films at room temperature with linearly polarized light of 514.5 nm, The experimental results showed that themagnetic response intensity of the TEMPO-PAZ could be easily controlled by choosing the appropriate polarized lightirradiating times, presumably due to the nitroxide radical in the TEMPO-PAZ molecular structure. For the polymerinvestigated here, the photoinduced alignment technique was introduced to increase the magnetic response intensity ofpolymer under irradiation, aiming originally at searching for a new photo-active organic magnetic multifunctional materials.On the other hand, experimental results also showed that the TEMPO-PAZ can be used as a material for optical image storage.