Light-induced Transformation Research Articles

Micro-Ring Morphology of Ag7NCs and Light-Induced Reversible Interconversion of FCC Ag14NCs via Cu2+ ions-Mediated Particle-Assisted Reversible Interconversion.

Despite the remarkable progress made on intercluster conversion in atomically precise metal nanoclusters (MNCs) and their self-organization to develop microscopic molecular architecture with well-defined size and shape, achieving light-induced reversible structural transformation and the development of micro-ring self-assembly in MNCs have, so far, remained elusive. The present investigation touches on these two long-standing quests by showcasing a new route, light-induced Particle-Assisted Reversible Interconversion (PARI) for the reversible transformation from Face Centered Cubic (FCC) Ag14NCs to Ag7NCs. Our studies reveal that the lack of plasmonic silver nanoparticles (AgNPs) in the system results in the formation of Ag7NCs with metallic kernels having centrosymmetric crystal packing. The molecular self-organization of Ag7NCs through various non-covalent interactions such as C-H⋅⋅⋅O, C-H⋅⋅⋅H-C, and C-H⋅⋅⋅π leads to the formation of micro-ring morphology, a unique molecular architecture in MNCs. The in situ generated AgNPs due to the acceleration of the reaction kinetics by Cu2+ ions facilitate the growth of Ag14NCs with FCC metallic kernel. These two structural units of AgNCs show light-induced reversible structural transformation which is also associated with the reversible tuning of their spectroscopic and morphological signatures. This PARI-guided interconversion strategy put forward a most appropriate example of a structure-property relationship in MNCs.

Light-induced transformation of all-inorganic mixed-halide perovskite nanoplatelets: ion migration and coalescence

When exposed to light, the colloidal perovskite nanoplatelets (NPLs) in the film can fuse into larger grains, and this phenomenon was thought to be closely related to ion migration. However, the available CsPbBr3 NPLs are not conducive to directly distinguishing this hypothesis. Herein, we prepare mixed-halide perovskite CsPbBr2.7I0.3 NPLs by a ligand-assisted reprecipitation method and investigate the photoluminescence evolution of NPLs under laser irradiation. At a low-irradiation intensity, 4.5-monolayer NPLs exhibit blue-shifted photoluminescence peaks due to the migration of iodide ions. Under higher laser fluence, a new photoluminescence component appears in the long wavelength region after the spectral blue shift, which is attributed to the coalescence of NPLs according to transmission electron microscopy analysis. A similar spectral evolution is also observed in 8-monolayer NPLs, while only the spectral blue shift caused by ion migration is detected in cuboidal CsPbBr2.7I0.3 nanocrystals. The use of strong bonding ligands can inhibit the fusion process of the NPLs, but not to impede ion migration, suggesting that fusion requires ligand detachment rather than ion migration. Similar suppression effects can be achieved in a vacuum atmosphere. Moreover, we demonstrate that mixed-halide NPLs can be used to realize anti-counterfeiting applications with superior photosensitivity.

Light-Induced Reactivity Switch at O2-Activating Bioinspired Copper(I) Complexes.

Using light to unveil unexplored reactivities of earth-abundant metal-oxygen intermediates is a formidable challenge, given the already remarkable oxidation ability of these species in the ground state. However, the light-induced reactivity of Cu-O2 intermediates still remains unexplored, due to the photoejection of O2 under irradiation. Herein, we describe a photoinduced reactivity switch of bioinspired O2-activating CuI complexes, based on the archetypal tris(2-pyridyl-methyl)amine (TPA) ligand. This report represents a key precedent for light-induced reactivity switch in Cu-O2 chemistry, obtained by positioning C-H substrates in close proximity of the active site. Open and caged CuI complexes displaying an internal aryl ether substrate were evaluated. Under light, a Cu-O2 mediated reaction takes place that induces a selective conversion of the internal aryl ether unit to a phenolate-CH2- moiety with excellent yields. This light-induced transformation displays high selectivity and allows easy postfunctionalization of TPA-based ligands for straightforward preparation of challenging heteroleptic structures. In the absence of light, O2 activation results in the standard oxidative cleavage of the covalently attached substrate. A reaction mechanism that supports a monomeric cupric-superoxide-dependent reactivity promoted by light is proposed on the basis of reactivity studies combined with (TD-) DFT calculations.

Light-induced phase transformation to two-dimensional amorphous spinel CoAlOx nanosheets as a tandem photothermal catalyst for efficient and durable toluene oxidation

Low temperature fabrication of spinel oxides and development of efficient and durable toluene photothermal catalysts remain challenging. Herein, two-dimensional amorphous spinel CoAlOx nanosheets (CoAl-LDH-L2) have been fabricated via a light-induced phase transformation strategy using intense photooxidation. Light-induced decomposition and phase transformation process have been used to elucidate the growth mechanism. The CoAl-LDH-L2 exhibits improved toluene adsorption and photothermal conversion, with the highest photothermal catalytic toluene conversion (∼100 % at 500 ppm) at 90 °C, outperforming most previously reported catalysts. Irradiation with mild external heating significantly increases the mineralization rate (∼90 %) and improves the long-term and cycling stability (∼5% losses within 39 h) relative to that under single-light-driven conditions. In-situ DRIFT spectroscopy was also performed for revealing the “tandem photothermal catalysis” mechanism for toluene conversion. This work offers a novel strategy for developing spinel oxides as low-temperature photothermal catalyst in a green and sustainable way.

In-situ formatting donor-acceptor polymer with giant dipole moment and ultrafast exciton separation

Donor-acceptor semiconducting polymers present countless opportunities for application in photocatalysis. Previous studies have showcased their advantages through direct bottom-up methods. Unfortunately, these approaches often involve harsh reaction conditions, overlooking the impact of uncontrolled polymerization degrees on photocatalysis. Besides, the mechanism behind the separation of electron-hole pairs (excitons) in donor-acceptor polymers remains elusive. This study presents a post-synthetic method involving the light-induced transformation of the building blocks of hyper-cross-linked polymers from donor-carbon-donor to donor-carbon-acceptor states, resulting in a polymer with a substantial intramolecular dipole moment. Thus, excitons are efficiently separated in the transformed polymer. The utility of this strategy is exemplified by the enhanced photocatalytic hydrogen peroxide synthesis. Encouragingly, our observations reveal the formation of intramolecular charge transfer states using time-resolved techniques, confirming transient exciton behavior involving separation and relaxation. This light-induced method not only guides the development of highly efficient donor-acceptor polymer photocatalysts but also applies to various fields, including organic solar cells, light-emitting diodes, and sensors.

Illuminating biomembranes: Light-induced control and transformation of membranes

Illuminating biomembranes: Light-induced control and transformation of membranes

Visible light-induced metal-free cascade denitrogenative borylation and iodination of nitroarenes.

An efficient method was developed for the one-pot construction of C-B and C-I via visible light-induced transformation of nitroarenes. This protocol relies on the photochemical properties of nitroarenes under visible light, followed by reduction with B2pin2 and diazotization with tBuONO. An array of arylboronates and iodobenzenes were constructed smoothly after excitation with purple LEDs at room temperature. In addition, the synthetic utility of this method was further demonstrated in the late-stage modification of a drug molecule. The advantages of this strategy include metal-free system, mild reaction conditions and acceptable substrate scope.

Transparent Organogels as a Medium for the Light-Induced Conversion from Spiropyran to Merocyanine.

Low-molecular-weight peptide gelators are a versatile class of compounds able to form gels under a variety of conditions, even via simple ultrasound sonication. In this paper, the ability of Boc-L-Phe-D-Oxd-L-Phe-OBn to gelate three organic solvents (toluene, tert-butyl methyl ether, and ethanol) was evaluated. The rheological behaviour of the materials was assessed via strain sweep analysis, while the fibrous network was analysed via optical microscopy on the wet gels. The gel obtained from toluene is a highly transparent material, and the one from ethanol appears translucent, while the one from tert-butyl methyl ether is opaque. These gels were used to study the reversible light-induced transformation from spyropiran (SP) to merocyanine (MC) and back, as a model system to check the effect of the gel medium onto the rection kinetic. We observed that the solvent used to form the organogels has a crucial effect on the reaction, as gels from aprotic solvents stabilize the SP form, while the ones from protic solvents stabilize the MC form. We thus obtained a solid support to stabilize the two photochromic species just by changing the solvent polarity. Moreover, we could demonstrate that the self-assembled gels do not interfere with the light-driven conversion process, either starting from SP or MC, thus representing a valid and economical photochromic material.

Modulation of magnetization dynamics of an Er(III) coordination polymer by the conversion of a ligand to a radical using UV light.

Light-induced substance conversion is highly promising for creating new radical-based compounds. Herein, we report an Er(III) coordination polymer [Er(CA)(ACA)(DMF)(H2O)]n (1) and its Y(III)-diluted analogue 1@Y (H2CA = 2,5-dichloro-3,6-dihydroxy-p-quinone, HACA = 9-anthracene carboxylic acid) with the light-induced transformation of the ligand to a radical. The χMT values of light-transformed products 1a and 1a@Y are higher than those of 1 and 1@Y, respectively, due to the formation of radicals by ultraviolet light irradiation, confirmed by EPR measurement as well. The effective energy barriers for magnetization reversal (Ueff) decrease from 72 K for 1 to 67 K for 1a, and from 117 K for 1@Y to 94 K for 1a@Y. This work not only provides a new light-conversion system but also reveals the nature of photo-induced variation of magnetic properties.

Mechanism of arsenic release from realgar oxidation in the presence of dissolved oxygen: Effect of reactive oxygen species and light-induced transformation

Oxidative dissolution of realgar is an important cause of arsenic (As) pollution in waters and soils. Generally, environmental factors including dissolved oxygen (DO) and solar radiation can lead to the formation of reactive oxygen species (ROS) on As-bearing metal sulfide minerals, which significantly promotes mineral oxidation and As release. Realgar is a typical nonmetallic sulfide mineral with excellent photochemical properties. However, the possible formation mechanism of ROS and the effect of solar radiation on realgar oxidation and the subsequent As release remain elusive. Here, the processes of realgar oxidation and As release were studied under darkness and solar radiation, and the influence of DO and pH on the reaction process was also investigated. The decomposition of H2O at the sulfur-defect sites and the oxidation of crystal surface As(II) by DO on realgar led to the formation of ROS including H2O2 and OH, which play a critical role in realgar oxidation and As release. Under solar radiation, the reactions between electrons and O2 on light-excited realgar promoted the production of O2−; while the realgar oxidation and As release could be mainly ascribed to the transformation of realgar to pararealgar in the presence of DO. Under atmospheric conditions, the release ratio of total As in realgar suspension was 4.2% under darkness, and increased to 18.1% under solar radiation. Both higher DO concentration and pH facilitated the generation of ROS and light-induced transformation of realgar to pararealgar, thereby promoting As release. These results imply that the ROS generated on realgar can induce its oxidation and As release in underground aquifers and sediments, and solar radiation may be an important factor causing As pollution in realgar tailings. The findings improve the understanding of As pollution in sulfide mineral mining areas.

S-Tetrazine-Bridged Photochromic Aromatic Framework Material.

Integrating fluorescent chromophores in aromatic frameworks could not only prevent aggregation-induced quenching caused by the π–π stacking interaction between the chromophore components but also confer new fluorescence properties. Herein, we report the fabrication of s-tetrazine-bridged aromatic frameworks TzAF by the incorporation of the smallest aromatic fluorophore, s-tetrazine (Tz), into the skeleton of a tetrahedrally connected lattice of aromatic frameworks. The thin films of TzAF coated on silica gel plates were found to exhibit reversible photoswitching fluorescence characteristics under alternate UV and visible-light irradiations with excellent fluorescence stability and high on/off contrast. The repeatable “on/off”fluorescence photoswitchability of the TzAF thin films was mechanistically attributed to light-induced reversible transformation between TzAF’s neutral and radical states.

Spectroscopic Identification of the Heterocumulenic Isocyanatoborane Radical HBNCO.

The highly elusive isocyanatoborane radical HBNCO has been generated by the reaction of laser-ablated boron atoms with HNCO and also by the light-induced chemical transformation of the hydrogen-bonded molecule-radical complex BNH···CO in solid neon matrix. IR spectroscopic and theoretical studies indicate that the HBNCO radical possesses a quasilinear B═N═C═O heterocumulenic structure with the unpaired electron mainly located at the boron atom. This is in sharp contrast to the bonding properties of the isoelectronic analogues HCCCO and NCCO, in which the unpaired electron is located at the terminal CO moiety.

Light-induced perovskite dynamic transformation enabling a photodetector to mimic a neuromorphic vision sensing system

In this work, we employ transformational NH4PbI3·MA as the photoactive material, which makes the photodetector exhibit short-term synaptic plasticity and realize image transmission and prepocessing functions of a neuromorphic vision sensing system.

Photorheological fluids of azobenzene polymers for lubrication regulation

Fluid viscosity is ubiquitous property and is of practical importance in intelligent fluids, industrial lubrication, and pipeline fluid transportation. Recently, there has been a surging interest in viscosity regulation. Here, we have developed a group of photorheological fluids by utilizing azobenzene polymers with a light-induced microstructure transformation. In this work, a photosensitive polymer with 4,4′-bis-hydroxyazobenzene as the main chain was designed and synthesized as a pivotal functional material. The sufficiently large structural difference under ultraviolet and near-infrared light makes it possible to regulate the viscosity of a polyethylene glycol solution. The viscosity of the photosensitive rheological fluids under ultraviolet light radiation is found to be up to 45.1% higher than that under near-infrared light radiation. To explore this intelligent lubricating technology, the friction regulation of ceramic sliding bearings was investigated utilizing photosensitive rheological fluids. Reversible friction regulation with a ratio of up to 3.77 has been achieved by the alternative irradiation of near-infrared and ultraviolet light, which can be attributed to the differences in mechanical properties and molecular structures under ultraviolet and near-infrared light according to both simulations and experiments. Such photorheological fluids will have promising applications in controllable lubrication, intelligent rheological fluids, and photosensitive dampers.

Effect of Solution pH on the Dual Role of Dissolved Organic Matter in Sensitized Pollutant Photooxidation.

Dissolved organic matter (DOM) has a dual role in indirect phototransformations of aquatic contaminants by acting both as a photosensitizer and an inhibitor. Herein, the pH dependence of the inhibitory effect of DOM and the underlying mechanisms were studied in more than 400 kinetic irradiation experiments over the pH range of 6–11. Experiments employed various combinations of one of three DOM isolates, one of two model photosensitizers, the model antioxidant phenol, and one of nine target compounds (TCs), comprising several aromatic amines, in particular anilines and sulfonamides, and 4-cyanophenol. Using model photosensitizers without antioxidants, the phototransformation of most TCs increased with increasing pH, even for TCs for which pH did not affect speciation. This trend was attributed to pH-dependent formation yields of TC-derived radicals and their re-formation to the parent TC. Analogous trends were observed with DOM as a photosensitizer. Comparison of model and DOM photosensitizer data sets showed increasing inhibitory effects of DOM on TC phototransformation kinetics with increasing pH. In systems with anilines as a TC and phenol as a model antioxidant, pH trends of the inhibitory effect could be rationalized based on the reduction potential difference (ΔEred) of phenoxyl/phenol and anilinyl/aniline couples. Our results indicate that the light-induced transformation of aromatic amines in the aquatic environment is governed by the pH-dependent inhibitory effects of antioxidant phenolic moieties of DOM and pH-dependent processes related to the formation of amine oxidation intermediates.

Optical Control of N-Methyl-d-aspartate Receptors by Azobenzene Quaternary Ammonium Compounds

Azobenzene-based quaternary ammonium compounds provide optical control of ion channels and are considered promising agents for regulation of neuronal excitability and for restoration of the photosensitivity of retinal cells. However, the selectivity of the action of these compounds remains insufficiently known. We studied the action of DENAQ (diethylamine-azobenzene-quaternary ammonium) and DMNAQ (dimethylamine-azobenzene-quaternary ammonium) on ionotropic glutamate receptors in rat brain neurons. In the dark, both compounds applied extracellularly caused fast and reversible inhibition of NMDA (N-methyl-d-aspartate) receptor-mediated currents with IC50 values of 10 and 5 μM, respectively. Light-induced transformation of DENAQ and DMNAQ to their cis forms caused the IC50 values to increase to 30 and 27 μM, respectively. Detailed analysis of this action revealed a complex nature consisting of fast inhibitory and slower potentiating effects. The AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors were only weakly affected independently on illumination. We conclude that, in addition to their long-lasting intracellular action, which persists after washout, azobenzene-based quaternary ammonium compounds should affect glutamatergic transmission and synaptic plasticity during treatment. Our findings also extend the list of soluble photoswitchable inhibitors of NMDA receptors. While the site(s) and mechanisms of action are unclear, the effect of DENAQ demonstrates strong pH dependence. At acidic pH values, DENAQ potentiates both NMDA and AMPA receptors.

Hymoins A-D: Two Pairs of Polyprenylated Acylphloroglucinols from Hypericum monogynum and Their Light-Induced Transformation.

Hymoins A-D (1-4), two pairs of light-induced transformative polyprenylated acylphloroglucinols with an unprecedented pentacyclic skeleton, were isolated from the flowers of Hypericum monogynum. The first decarbonylative ring contraction of complex natural products was investigated by light irradiation. Their structures were elucidated by nuclear magnetic resonance analysis, X-ray crystallography, and electronic circular dichroism calculations. In addition, compound 3 showed moderate inhibition efficacy of the platelet-activating-factor-induced aggregation of rabbit platelets.

Photoelectrochemistry of Au Nanocluster-Sensitized TiO2: Intricacy Arising from the Light-Induced Transformation of Nanoclusters into Nanoparticles

Investigating photoelectrode interfaces is challenging due to complex charge carrier pathways, and photodegradation aggravates this difficulty because interfacial properties are significantly alter...

Facile Light-Induced Transformation of [RuII(bpy)2(bpyNO)]2+ to [RuII(bpy)3]2.

Ru-based coordination compounds have important applications as photosensitizers and catalysts. [RuII(bpy)2(bpyNO)]2+ (bpy = 2,2'-bipyridine and bpyNO = 2,2'-bipyridine-N-oxide) was reported to be extremely light-sensitive, but its light-induced transformation pathways have not been analyzed. Here, we elucidated a mechanism of the light-induced transformation of [RuII(bpy)2(bpyNO)]2+ using UV-vis, EPR, resonance Raman, and NMR spectroscopic techniques. The spectroscopic analysis was augmented with the DFT calculations. We concluded that upon 530-650 nm light excitation, 3[RuIII(bpyNO-•)(bpy)2]2+ is formed similarly to the 3[RuIII(bpy-•)(bpy)2]2+ light-induced state of the well-known photosensitizer [RuII(bpy)3]2+. An electron localization on the bpyNO ligand was confirmed by obtaining a unique EPR signal of reduced [RuII(bpy)2(bpyNO-•)]+ (gxx = 2.02, gyy = 1.99, and gzz = 1.87 and 14N hfs Axx = 12 G, Ayy = 34 G, and Azz = 11 G). 3[RuIII(bpyNO-•)(bpy)2]2+ may evolve via breaking of the Ru-O-N fragment at two different positions resulting in [RuIV═O(bpy)2(bpyout)]2+ for breakage at the O-|-N bond and [RuII(H2O)(bpy)2(bpyNOout)]2+ for breakage at the Ru-|-O bond. These pathways were found to have comparable ΔG. A reduction of [RuIV═O(bpy)2(bpyout)]2+ may result in water elimination and formation of [RuII(bpy)3]2+. The expected intermediates, [RuIII(bpy)2(bpyNO)]3+ and [RuIII(bpy)3]3+, were detected by EPR. In addition, a new signal with gxx = 2.38, gyy = 2.10, and gzz = 1.85 was observed and tentatively assigned to a complex with the dissociated ligand, such as [RuIII(H2O)(bpy)2(bpyNOout)]3+. The spectroscopic signatures of [RuIV═O(bpy)2(bpyout)]2+ were not observed, although DFT analysis and [RuII(bpy)3]2+ formation suggest this intermediate. Thus, [RuII(bpy)2(bpyNO)]2+ has potential as a light-induced oxidizer.

Visible light-mediated, rose Bengal-catalyzed oxidative radical C[sbnd]H cyclization of alkyl 1,1′-biaryl-2-ones: An efficient synthesis of 10-alkylphenanthren-9-ols in water

A visible light-mediated (blue LED: λ = 455 ± 10 nm), rose bengal-catalyzed intramolecular cycloaromatization reaction of alkyl 1, 1′-biaryl-2-ones for the synthesis of 10-alkylphenanthren-9-ols in water under open air atmosphere at ambient conditions has been developed. Experimental studies demonstrate that the reaction proceeded via a radical pathway. This protocol is applicable to a wide variety of substrates giving expected 10-alkylphenanthren-9-ols in good yields, appropriate for the gram-scale synthesis, atom economy, and eco-friendly as compared to literature reported methodology for the preparation of phenanthrol derivatives. Moreover, to the best of our knowledge, no instance has hitherto been accounted on the visible light-induced transformation of readily available alkyl 1,1′-biaryl-2-ones to 10-alkylphenanthren-9-ols.