Photoinduced Conversion Research Articles

Structural investigation of the high spin→low spin relaxation dynamics of the porous coordination network [Fe(pz)Pt(CN)4]⋅2.6 H2O.

The Hoffman-type coordination compound [Fe(pz)Pt(CN)4]⋅2.6 H2O (pz = pyrazine) shows a cooperative thermal spin transition at around 270 K. Synchrotron powder X-Ray diffraction studies reveal that a quantitative photoinduced conversion from the low-spin (LS) state into the high-spin (HS) state, based on the light-induced excited spin-state trapping effect, can be achieved at 10 K in a microcrystalline powder. Time-resolved measurements evidence that the HS→LS relaxation proceeds by a two-step mechanism: a random HS→LS conversion at the beginning of the relaxation is followed by a nucleation and growth process, which proceeds until a quantitative HS→LS transformation has been reached.

Photo-induced conversion from supramolecular to covalently linked polymers based on anthracene-appended amphiphiles

A photo-induced conversion from supramolecular to covalent polymers was achieved based on anthracene-appended amphiphiles.

Experimental observations of photo-induced bond conversions in GeAsS thin films

Photo-induced anisotropy phenomena have been investigated in Ge25As30S45 chalcogenide glassy thin-films prepared by the electron beam evaporation technique. Thin-films of thicknesses ranging from 3 to 7μm were prepared, annealed slightly below the glass transition temperature Tg and characterized by means of optical transmission, thermal analysis, elemental microanalysis through energy dispersive X-ray spectroscopy and by micro-Raman spectroscopy. Photo-induced dichroism (PID) was studied using band gap 514nm laser excitation. Its kinetics was studied by observing the transmission and reflection of the film at different excitation intensities and temperatures. The conversion of homopolar (Ge–Ge, As–As) toward heteropolar (Ge–S, As–S) bonds was confirmed by polarized micro-Raman spectroscopic studies.A phenomenological unipolar model, that suggests the presence of photo induced bond changes through an energetic barrier (estimated at 14kJ/mol), is proposed to explain the experimentally observed non-monotonic behavior of PID.

Metal-free synthesis of E-vinylphosphonates via photoinduced alkyne hydrophosphonylation and thiol promoted isomerization sequence

The alkyne hydrophosphonylation is an atom economical method for the synthesis of vinylphosphonates that are compounds of both biological and synthetic relevance. Recent approaches based on the use of metal catalysts have only partially solved the problems of the reaction selectivity as well as of economical and large amount production. We report in this Letter on a metal-free approach that leads to E-vinylphosphonates in high yields. The approach is based on a two-step one-pot synthesis, namely: (a) photoinduced anti-Markovnikov addition of a H-phosphonate to alkynes to give mixtures of E- and Z-vinylphosphonates, and (b) cysteine promoted photoinduced conversion of the crude mixtures of adducts into E-isomers (58–92% overall yields).

WO3/TiO2 core–shell nanostructure for high performance energy-saving smart windows

The electrochromic, photodegradation, and photoinduced hydrophilicity properties of the WO3/TiO2 core–shell nanostructure as a smart building material for energy-saving are investigated. The core–shell nanostructure exhibits a highly reduced ion intercalation capacity with good reversible electrochemical cycling of intercalation–deintercalation, and shows a higher coloration efficiency (110.8cm2C−1), faster switching speed (0.7s and 2.9s) and better cycling performance than as-deposited WO3 nanowires (NWs). The TiO2 shell layer greatly enhanced the photocatalytic oxidation activity of WO3 NWs, increasing the photoinduced hydrophilic conversion. The enhanced photocatalytic reaction by the core–shell structure was attributed to the multi-electron reduction in the interlayer, caused by the electrons injected from the conduction band of the WO3 NWs. These results suggest that the WO3/TiO2 core–shell nanostructure enhances the electrochromic, photodegradation, and photoinduced hydrophilicity properties due to the increased density of charge separated electron–hole pairs aided by the TiO2 and WO3 interlayer. The WO3/TiO2 core–shell structure was found to possess superior properties giving it good potential for use in energy-saving smart windows.

Giant bulk photovoltaic effect in thin ferroelectricBaTiO3films

The voltage generated in a noncentrosymmetric crystal due to the bulk photovoltaic effect (BPE) can greatly exceed the energy gap, however, the light energy conversion efficiency is extremely low. Here we show that the BPE is remarkably enhanced in the case of thin films. The measurements of the BPE in heteroepitaxial single domain ferroelectric ${\mathrm{BaTiO}}_{3}$ thin films reveal the enhancement of both photoinduced electric field and conversion efficiencies of the BPE by more than 4 orders of magnitude. Besides the fundamental aspect, our results indicate the potential for the use of the BPE in photovoltaic applications.

Sunlight-driven synthesis of anisotropic silver nanoparticles

Abstract Photoinduced shape conversion of silver nanoparticles was realized using sunlight. The silver seeds were transformed to silver nanoprisms under sunlight when the concentration of citrate was low (⩽5.0 × 10 −4 M). Nevertheless, sunlight converted the obtained silver nanoprisms to silver nanodecahedrons when the concentration of citrate in reaction system was increased. It was found that the ultraviolet light from sunlight played a vital role in the shape conversion from nanoprism to nanodecahedron. Lighting power density did not influence the shape conversion except for reaction rate. Besides, the silver nanodecahedrons were synthesized in the mixed solution of AgNO 3 and citrate in absence of silver seeds through irradiation by simulated sunlight. The mechanism on the sunlight induced synthesis of silver nanoparticles was discussed. Anisotropic silver nanoparticles including nanoprisms and nanodecahedrons were obtained through controlling the citrate concentration and irradiation time by sunlight from green light source.

Photoinduced conversion of methane into benzene over GaN nanowires.

As a class of key building blocks in the chemical industry, aromatic compounds are mainly derived from the catalytic reforming of petroleum-based long chain hydrocarbons. The dehydroaromatization of methane can also be achieved by using zeolitic catalysts under relatively high temperature. Herein we demonstrate that Si-doped GaN nanowires (NWs) with a 97% rationally constructed m-plane can directly convert methane into benzene and molecular hydrogen under ultraviolet (UV) illumination at rt. Mechanistic studies suggest that the exposed m-plane of GaN exhibited particularly high activity toward methane C-H bond activation and the quantum efficiency increased linearly as a function of light intensity. The incorporation of a Si-donor or Mg-acceptor dopants into GaN also has a large influence on the photocatalytic performance.

Comparative study of photoinduced wettability conversion between [PW12O40]3−/brookite and [SiW12O40]4−/brookite hybrid films

Two tungsten-based Keggin-type heteropolyacids (PW12: ([PW12O40]3−) and SiW12: ([SiW12O40]4−)) were hybridized with brookite-type TiO2. Then photocatalytic decomposition activity, photoinduced hydrophilicity, and sustainability of the hydrophilicity in the dark were evaluated using gaseous 2-propanol (IPA) decomposition and sessile drop method. The obtained films were transparent in the visible wavelength range. Both hybrid films exhibited higher photocatalytic decomposition activity and had higher photoinduced hydrophilicizing rates than pure brookite films under UV illumination. The PW12/TiO2 film exhibited better photocatalytic performance than the SiW12/TiO2 film did. Atmosphere dependence, XPS analysis, and electrochemical experiments indicated the cause of these two films' different levels of sustainability of hydrophilicity to be differences in their electron storage capability. Results show that the electron scavenger capability and reoxidation efficiency of the heteropolyacid are key factors affecting the overall performance of wettability conversion of this hybrid film system before and after UV illumination.

The role of iron(ii) dilution in the magnetic and photomagnetic properties of the series [FexZn1−x(bpp)2](NCSe)2

The effects of metal dilution on the spin-crossover behavior of iron(II) in the mixed crystal series [Fe(x)Zn(1-x)(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) have been studied using magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. For each mixed-crystal system, the thermal spin transition temperature, T(1/2), and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T(1/2) decreases with the metal dilution while T(LIESST) remains unchanged. Dilution also tends to decrease the hysteresis width and smooth the transition curves. These effects were discussed first qualitatively and then quantitatively on the basis of a kinetic study governing the photo-induced back conversion taking into account the relative sizes of Zn(II) and Fe(II) ions. Interestingly, single crystals were obtained for [Fe(0.6)Zn(0.4)(bpp)2](NCSe)2 allowing the X-ray diffraction crystal-structure determination.

Tracing the slow photon effect in a ZnO inverse opal film for photocatalytic activity enhancement

Highly ordered, dense and continuous ZnO inverse opal (ZnO-IO) films with different air sphere sizes have been successfully prepared by a metal salt-based sol–gel infiltration method and used to prove and demonstrate the slow photon effect occurrence to enhance the photocatalytic activity. The obtained ZnO-IO films have a pure wurzite structure with similar crystallite size according to the XRD experiments and show very ordered macroporous structures from SEM and TEM analyses. The ZnO-IO films present a photoinduced surface wettability conversion phenomenon and the wettability of the ZnO film can be tuned from superhydrophobicity to hydrophilicity after UV-vis irradiation. Compared with the ZnO film without inverse opal structure, both ZnO-IO films demonstrate highly enhanced photocatalytic activities due to the hierarchically macro–mesoporous structure and particularly the slow photon enhanced light absorption. The synergy of the slow photon effect and hierarchically porous structure of inverse opal itself results in the highest photocatalytic activity at an incident light angle of θ = 40°. Moreover, our results suggest that the slow photon effect occurring at the red edge of PBG exhibits a higher photocatalytic reaction rate than that at the blue edge of PBG. The extraordinary enhancement of the photocatalytic activity via changing the incident light angle reveals that the slow photon effect does take place and further dramatically enhance the photocatalytic activity of ZnO-IO films. This work may open an exciting door to all the fields related to light absorption, such as solar cells, and optical and electro-optical devices.

Photoinduced reversible shape conversion of silver nanoparticles assisted by TiO₂.

Silver nanoprisms were transformed into nanodecahedra through photoinduction of ultraviolet (UV) light in the presence of titanium dioxide (TiO2) quantum dots (QDs). Subsequently, the silver nanodecahedra were reconverted to silver nanoprisms under sodium lamp if there was sufficient citrate in the reaction system. The localized surface plasmon resonance (LSPR) optical properties of silver nanoparticles were tuned during photoinduced shape conversion. The photocatalytic activity of TiO2 QDs assisted the conversion of prisms to decahedra upon UV light irradiation. Nevertheless, the presence of TiO2 did not inhibit the photoinduced reconversion from decahedra to prisms by sodium light. It was demonstrated that citrate was indispensable in the photoinduction process. In addition, oxygen in solution played a vital role in the reversible shape conversion of silver nanoparticles. Moreover, simulated sunlight can convert silver nanoprisms to nanodecahedra instead of UV light with assistance of TiO2 QDs, which would promote the photoinduced reaction of silver nanoparticles based on a natural light source.

Tuning chelating groups and comonomers in spiropyran-containing copolymer thin films for color-specific metal ion binding

Photochromic molecules can be used to selectively bind divalent metal ions. In order to study the influence of increased chelation in spiropyran-containing copolymers, we synthesized two derivatives: spiropyran methacrylate (SPMA) and spiropyran methacrylate with a methoxy substituent in the 8′ position of the benzopyran ring (MEO). Additionally, the comonomer with which spiropyran was polymerized is also varied between methyl methacrylate (MMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) to tune the colorimetric response. Fourier transform-infrared (FT-IR) spectroscopy was used to characterize the photoinduced conversion of spiropyran to merocyanine, as well as the merocyanine–metal ion (MC–M2+) interaction. By means of UV-Vis absorption spectroscopy, we demonstrate that each metal ion gives rise to a unique colorimetric response for the various spiropyran-containing copolymers studied.

Plasmon‐Mediated Syntheses of Metallic Nanostructures

The ability to prepare noble metal nanostructures of a desired composition, size, and shape enables their resulting properties to be exquisitely tailored, which has led to the use of these structures in numerous applications, ranging from medicine to electronics. The prospect of using light to guide nanoparticle reactions is extremely attractive since one can, in principle, regulate particle growth based on the ability of the nanostructures to absorb a specific excitation wavelength. Therefore, using the nature of light, one can generate a homogenous population of product nanoparticles from a heterogeneous starting population. The best example of this is afforded by plasmon-mediated syntheses of metal nanoparticles, which use visible light irradiation and plasmon excitation to drive the chemical reduction of Ag(+) by citrate. Since the initial discovery that Ag triangular prisms could be prepared by the photo-induced conversion of Ag spherical nanoparticles, plasmon-mediated synthesis has become a highly controllable technique for preparing a number of different Ag particles with tight control over shape, as well as a wide variety of Au-Ag bimetallic nanostructures. We discuss the underlying physical and chemical factors that drive structural selection and conclude by outlining some of the important design considerations for controlling particle shape as learned through studies of plasmon-mediated reactions, but applicable to all methods of noble metal nanocrystal synthesis.

Photoinduced Reactions of Surface-Bound Species on Titania Nanotubes and Platinized Titania Nanotubes: An in Situ FTIR Study

Photoinduced conversion of surface-bound species on titania nanotubes that were first oxidized and then reduced (Ti–NT–O2–H2) and on platinized titania nanotubes subjected to oxidation and reduction (Pt–Ti–NT–O2–H2) has been investigated by means of in situ FTIR spectroscopy. Bidentate and monodentate carbonates as well as bicarbonates and carboxylates are formed subsequent to exposure of both Ti–NT–O2–H2 and Pt–Ti–NT–O2–H2 to CO2. Formic acid was only observed on Pt–Ti–NT–O2–H2. UV illumination of the nanotubes led to an increase in the number of surface-bound species as a result of the further reaction with gas-phase CO2 with a greater increase in surface species on Ti–NT–O2–H2 than on Pt–Ti–NT–O2–H2. The underlying basis of the photoinduced increase in adsorbed species is discussed for both types of nanotubes. Photoinduced reactions of surface species also take place and are remarkably different on the two types of nanotubes. UV illumination of Ti–NT–O2–H2 converts bidentate carbonates and bicarbonates...

Photochemical reaction of 2-chlorobiphenyl with N(III) (H2ONO+/HONO/NO2−) in acidic environment studied by using co-linear laser flash photolysis

Photo-induced transformation in the presence of N(III) is an important pathway for pollutants conversion in atmospheric condensed phase. In this study, the photochemical reaction between 2-chlorobiphenyl and N(III) was investigated in acidic environment by using co-linear laser flash photolysis technique. The photo-induced conversion of 2-PCB is initiated from its rapid oxidation by OH, a primary product from the photolysis of N(III). The second-order rate constant for the reaction between 2-PCB and OH was determined to be (8.9 ± 1.2) × 109 M−1 s−1. HONO and NO2− were found to be more important than H2ONO+ with respect to the photochemical transformation of pollutants in atmospheric hydrometeors. The complicated photochemical conversion pathways and their significance in the atmosphere were discussed as well in this paper.

Surface pattern based on an azobenzene-containing copolymer thin film and its light-driven morphology modulation

A type of azobenzene-containing block copolymer polymethyl methacrylate-b-poly (n-butylmethacrylate-co-6-(4-(phenylazo) benzoate) hexyl methacrylate) (PMMA-b-(PnBMA-co-PAzoMA)) was synthesized by the atom transfer radical polymerization (ATRP). Macroinitiator polymethyl methacrylate (PMMA) was prepared by ATRP and used to initiate the copolymerization of monomern-butyl methacrylate (nBMA) and azobenzene-based methacrylate monomer (AzoMA). Herein, three block copolymers with different molecular weights and block volume fractions were obtained and spin-coated on a silicon substrate or quartz plate before annealing at 180 °C for 14 h. The surface morphologies in these annealed copolymer films were observed by atomic force microscopy (AFM). Bicontinuous stripe or island patterns with different sizes were formed dependent on the film thickness. These ordered patterns are considered to be formed arising from the dewetting process of the surface layer in the copolymer film. Photoisomerization of azobenzene units in the copolymer films changed the dewetting behaviors of the surface layer of the thin film. Therefore, some copolymer annealed films showed a reversible morphology conversion between bicontinuous stripe and island structure when exposed to UV light and upon being stored in the dark. It was found that the composition of the block copolymer had obvious influences on the photoinduced morphology conversion behaviors in these copolymer thin films. When the volumes of PnBMA and PAzoMA phases in the block copolymer were large enough, the surface morphology could be modulated by UV light irradiation and storage in the dark. This work proposes a new possibility for photoinduced control and design of the dewetting processes of thin films using a linear block copolymer.

Factors Affecting UV-Induced Superhydrophilic Conversion of a TiO2 Surface

The present study explored the effects of several factors (wetting, light intensity, spectral variation of the actinic light, heating, and surface acidity) on the hydrophilic conversion of the surface of TiO2 nanocoatings. The experimental dependencies of the efficiencies of photoinduced hydrophilic surface conversion on the intensity and wavelength of the actinic light clearly indicate the role of electronic photoexcitation in hydrophilic surface transformation. Particularly, the maximum extrema in spectral dependence of the efficiency of photoinduced hydrophilic conversion correspond to the energies of the first indirect and first direct electronic band-to-band transitions in TiO2. At the same time, temperature dependence and the effect of the surface acidity on the hydrophilic behavior of the TiO2 surface demonstrate the importance of the multilayer hydrate structure in both the original hydrophilicity of the surface and the direction of the photoinduced hydrophilic conversion. Estimation of the surfac...

Effect of pressure on photochromic furylfulgide

The effect of pressure on photochromic furylfulgide is investigated using monodispersed molecules in solution and molecules in a single crystal by measuring the optical absorption at room temperature under pressure provided using a diamond anvil cell. Monodispersed open-ring (E-form) and closed-ring (C-form) isomers in solution are stable under high pressure; however, pressure-induced E → C isomerisation is observed in a single crystal composed of E-form molecules above 3.0 GPa without UV irradiation. Photochromism of furylfulgide can be observed under high pressures up to 5.0 GPa in both monodispersed molecules and single crystals. In a single crystal, photoinduced conversion from the E-form to the C-form accelerates above a critical value when the fraction of C-form molecules becomes relatively large; this critical value depends on the applied pressure. The acceleration is due to the effect of the surrounding molecules, i.e., destabilisation of E-form molecules surrounded by a sufficient number of photoconverted C-form molecules results in conversion of the E-form molecule without the absorption of a photon.

Isolation and Photoinduced Conversion of 6-epi-Stephacidins from Aspergillus taichungensis

Three prenylated indole alkaloids with a rare anti bicyclo-[2.2.2]diazaoctane core ring (5-7) were isolated from Aspergillus taichungensis. The structures including absolute configurations were elucidated based on NMR, X-ray, and CD methods. (+)-Versicolamides B and C (8-9) which contain a spiro-center, together with seven analogues (7, 10-15), were isolated as photoinduced conversion products of 6. Biological evaluation indicated that 6 and 7 exhibited significant cytotoxicities with IC50 values in the low micromolar range.