Visible Light Energy Research Articles

Complete surface coverage of ZnO nanorod arrays by pulsed electrodeposited CuInS2 for visible light energy conversion

Well-aligned ZnO nanorods were uniformly coated with a layer of CuInS2 nanoparticle photosensitizers using a tailored sequential pulsed electrodeposition. The formation of CuInS2-ZnO heterojunction with well-matched band energy alignment and the superior electron mobility in ZnO nanorods led to a remarkable 3.75 times improved photoelectrochemical performance of the electrode under visible light irradiation.

BODIPY functionalized o-carborane dyads for low-energy photosensitization.

A new type of organic dyad that can induce low-energy photosensitization has been developed; electron donor and electron acceptor units are boron dipyrromethene (BODIPY) and ortho-carborane (o-Cb), respectively. The new dyads consist of a V-shaped BODIPY-(o-Cb)-BODIPY molecular array in which two BODIPY units are substituted onto two adjacent carbon atoms of the central o-Cb. In the presence of the o-Cb unit, as an electron acceptor, significant fluorescence quenching was observed which indicated that photoinduced electron transfer (PET) had occurred from the end-on BODIPY units to the central o-Cb with PET efficiencies of 63-71%. As a result, the corresponding cationic and anionic species that are responsible for the charge transfer state were detected by the serial spectroelectrochemical studies: cationic BODIPY radicals at 400 nm at the applied voltage of 1.44 V and broad absorption bands of anionic o-Cb radicals in the range of 250-490 nm at -1.84 V. Transient absorption studies further confirmed the BODIPY radical anion at 540 nm and the o-Cb radical anion at 350-475 nm with a structureless broad band.

Steric and Electronic Factors Associated with the Photoinduced Ligand Exchange of Bidentate Ligands Coordinated to Ru(II).

In an effort to create a molecule that can absorb low energy visible or near-infrared light for photochemotherapy (PCT), the new complexes [Ru(biq)2 (dpb)](PF6 )2 (1, biq = 2,2'-biquinoline, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline) and [(biq)2 Ru(dpb)Re(CO)3 Cl](PF6 )2 (2) were synthesized and characterized. Complexes 1 and 2 were compared to [Ru(bpy)2 (dpb)](PF6 )2 (3, bpy = 2,2'-bipyridine) and [Ru(biq)2 (phen)](PF6 )2 (4, phen = 1,10-phenanthroline). Distortions around the metal and biq ligands were used to explain the exchange of one biq ligand in 4 upon irradiation. Complex 1, however, undergoes photoinduced dissociation of the dpb ligand rather than biq under analogous experimental conditions. Complex 3 is not photoactive, providing evidence that the biq ligands are crucial for ligand photodissociation in 1. The crystal structures of 1 and 4 are compared to explain the difference in photochemistry between the complexes. Complex 2 absorbs lower energy light than 1, but is photochemically inert although its crystal structure displays significant distortions. These results indicate that both the excited state electronic structure and steric bulk play key roles in bidentate photoinduced ligand dissociation. The present work also shows that it is possible to stabilize sterically hindered Ru(II) complexes by the addition of another metal, a property that may be useful for other applications.

Low energy light induced DNA photocleavage with a bis-ruthenated porphyrin

When the new porphyrin 5,15-(4-pyridyl)-10,20-(4-trifluoromehtylphenyl)porphyrin is reacted with two equivalents of Ru(bipy)2Cl2 (where bipy=2,2′-bipyridine) formation of the target ruthenated porphyrin is achieved with 57% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrins Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dπ) to bipy(π∗) metal to ligand charge transfer (MLCT) band. The bipyridyl π to π∗ transition occurs at 295nm. Cyclic voltammetry experiments of the porphyrin indicate porphyrin centered reductions in the cathodic direction with no noticeable oxidation process within the window scanned. The ruthenated porphyrin shows the characteristic quasireversible redox couple in the anodic region indicative of oxidation of Ru(II) to Ru(III). A single redox couple for Ru(III/II) indicates no electronic interaction between the ruthenium moieties. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give an unusually large binding constant Kb=(1.1±0.7)×106M−1 indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 550nm) complete nicking of the DNA is observed.

Visible Light Photoredox Catalyzed Biaryl Synthesis Using Nitrogen Heterocycles as Promoter

Although transition-metal-catalyzed direct arylation of aromatic C–H bonds is one of the most efficient ways for the construction of biaryl targets, it is also expected for other alternative methods that can use inexpensive catalysts and abundant solar energy to drive chemical reactions. Herein, we describe a new activation mode for biaryl synthesis by using a photosensitive complex of potassium tert-butoxide (KOt-Bu) and nitrogenous heterocyclic ligands via visible light excitation. Under low-energy visible light irradiation, the single-electron transfer from electron-donor KOt-Bu to electron-deficient nitrogenous heterocycle occurred in the inner part of the complex by using potassium as a bridge atom. The ligand accepted the as-photoexcited single electron and transformed into stable radical anions which played a dominant role in the coupling reactions of benzene with aryl halides at ambient temperature. This reaction paradigm features the use of inexpensive catalyst, abundant visible light energy, and...

Degradation of Rhodamine B by Highly Efficient Photocatalyst TiO<sub>2</sub>-Ag/Ag<sup>+</sup> under Simulated Sunlight Irradiation

nanosized Ag/Ag3PO4 doped titanium dioxide (TiO2) particulates (TiO2-Ag/Ag3PO4) were synthesized by sol-gel process. TiO2-Ag/Ag3PO4 was used to coat on the glass tubes interfaces to investigate the photocatalytic effect against Rhodamine B under simulated solar light. The calcination temperature and time, number of coating layers, dopant ratio of Ag was optimized. It is noted that the photocatalytic effect under simulated solar was 99.8% only for 60min, which is much higher than pure TiO2. The hybrid material was characterized using X-ray diffractometer (XRD), SEM and UV–vis spectroscopy (UV–vis). By the result, it is noticed that pure Ag and Ag3PO4 particles were combined with TiO2 nanoparticles, and TiO2-Ag/Ag3PO4 thin film exhibited significantly better photocatalytic effect due to its narrow band gap energy (2.26 eV) and higher visible light absorbing ability. The stability of TiO2-Ag/Ag3PO4 material was also investigated.

Photothermally triggered fast responding hydrogels incorporating a hydrophobic moiety for light-controlled microvalves.

Iron oxide nanoparticles dispersed within a thermally responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel matrix effectively convert the photo energy of visible light of modest intensity into thermal energy, providing the efficient means to trigger changes in volumetric swelling of hydrogels. However, long irradiation time (on the order of minutes) and modest volume change limit their applications that need fast response and/or large volume change. In this work, we found that the degree of volume change triggered by light could be maximized by adjusting the lower critical solution temperature (LCST) of the hydrogels. On the basis of the evidence in this investigation, we can develop highly responsive hydrogels that show rapid and significant light-induced volume change, which could be achieved by incorporating a hydrophobic N,N-diethylacrylamide moiety in the PNIPAm network. This enhanced responsiveness led to the successful application of this material in a remote-controllable microvalve for microfluidic devices operated by light illumination within a few seconds.

Oxide-based chromogenic coatings and devices for energy efficient fenestration: Brief survey and update on thermochromics and electrochromics

Modern buildings often have large windows and glass facades in order to achieve good day-lighting and desirable indoors–outdoors contact. These glazings are challenging with regard to the buildings' energy efficiency and frequently let in or out too much energy; this phenomenon has to be balanced by energy guzzling cooling or heating. In particular, the cooling requirement has grown strongly in recent years. Chromogenic glazings, based on thermochromism or electrochromism, are emerging technologies that can regulate the inflow of visible light and solar energy between widely separated limits and create better energy efficiency than is possible with static solutions. Thermochromic thin films—in practice based on vanadium dioxide—have a transmittance of infrared solar radiation that is smaller at high temperature than at low temperature. Electrochromic multilayer structures—often incorporating nanoporous thin films of tungsten oxide and nickel oxide—are able to vary the transmittance of visible light and solar energy when a low voltage is applied for a short time so as to shuttle charge between the two oxide films. Furthermore, and importantly, the new chromogenic fenestration technologies are able to improve indoor comfort. This brief tutorial review surveys the fields of oxide-based thermochromics and electrochromics with particular attention to recent advances.

Evidence and conjecture about mechanisms of cutaneous disease in photodermatology.

Photosensitivity disorders are caused by a variety of mechanisms. Three common themes are as follows: excess chromophore allowing visible light energy to cause photodynamic damage, reduced DNA repair capacity to UV-induced DNA damage, and enhanced sensitivity to light-induced allergens mediated immunologically. Although the cause of each condition may be known, the precise pathogenesis underlying the photosensitivity has taken longer to understand. By focussing on three clinical disorders under each of these themes, we have explored the following: why erythropoietic protoporphyria differs so markedly from the other cutaneous porphyrias; how a DNA repair defect was eventually revealed to be the underlying cause of the vitamin B3 deficiency disorder of pellagra; an immunological explanation for the over reactivity to photoallergens in chronic actinic dermatitis.

Photoinduced Electron Transfer–Reversible Addition–Fragmentation Chain Transfer (PET-RAFT) Polymerization of Vinyl Acetate andN-Vinylpyrrolidinone: Kinetic and Oxygen Tolerance Study

Photoinduced electron transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization was employed for the polymerization of unconjugated monomers, including vinyl acetate, vinyl pivalate, N-vinylpyrrolidinone, dimethyl vinylphosphonate, vinyl benzoate, and N-vinylcarbazole, in the presence of low concentration (ppm range) of photoredox catalyst, fac-[Ir(ppy)3], under low energy visible light irradiation. Kinetic studies of vinyl acetate indicated excellent control of molecular weights and molecular weight distributions (Mw/Mn = 1.09–1.2), even with high monomer conversion (>75%), in different catalyst concentrations. High molecular weights of poly(vinyl acetate) (Mn > 100 000 g/mol) and poly(N-vinylpyrrolidinone) (Mn > 40 000 g/mol) with low dispersities (Mw/Mn < 1.25) were obtained in bulk polymerizations. Moreover, the online kinetic study using Fourier transform near-infrared (FTNIR) showed comparable kinetic rates for the polymerizations in the absence and presence of relatively l...

Aqueous photoinduced living/controlled polymerization: tailoring for bioconjugation

We report a photoinduced living polymerization technique able to polymerize a large range of monomers, including methacrylates, acrylates and acrylamides, in water and biological media as well as organic solvents. This polymerization technique employs ultra-low concentrations of a ruthenium-based photoredox catalyst (typically 1 ppm to monomers) and enables low energy visible LED light to afford well-defined polymers with narrow polydispersities (Mw/Mn < 1.3). In this paper, different parameters, including photocatalyst concentrations and solvent effects, were thoroughly investigated. In addition, successful polymerizations in biological media have been reported with good control of the molecular weights and molecular weight distributions (Mw/Mn < 1.4). Finally, protein–polymer bioconjugates using a “grafting from” approach were demonstrated using bovine serum albumin as a model biomacromolecule. The enzymatic bioactivity of the protein was demonstrated to be maintained using a standard assay.

Magnetic and optical properties of N-doped, Fe-doped and (N, Fe)-codoped anatase TiO2

Electronic structure, magnetic and optical properties of N-doped, Fe-doped and N, Fe-codoped anatase TiO2 have been investigated by using first-principles calculations. Both N-doped and Fe-doped anatase TiO2 exhibit ferromagnetic semiconductors, while N, Fe-codoped one manifests metallic nature with antiferromagnetic ground state. The optical absorption spectrum for all the doped models extends the optical absorption to the visible-light region. Especially, N, Fe-codoped anatase TiO2 presents the highest absorption coefficient during the visible-light energy range (1.63–3.1eV). Furthermore, the ultraviolet absorption is also enhanced, particularly for N-doped model.

Electron–Hole Pair Generation of the Visible-Light Plasmonic Photocatalyst Ag@AgCl: Enhanced Optical Transitions Involving Midgap Defect States of AgCl

We explored how the visible-light energy absorbed by noble-metal nanoparticles (NPs) is converted to electrons and holes in the semiconductor in a visible-light plasmonic photocatalyst by studying the representative system Ag@AgCl on the basis of density functional calculations and classical electrodynamics calculations. These calculations suggest that the energy transfer from the Ag NPs to the semiconductor AgCl requires the presence of midgap defect states in the semiconductor and that the surface plasmon resonance (SPR) of the Ag NPs strongly enhances the optical transitions of the semiconductor involving the defect states. We verified this suggestion experimentally by preparing Ag@AgCl samples possessing different degrees of bulk and surface defects and subsequently by carrying out photodegradation experiments using these samples.

Solar Synthesis: Prospects in Visible Light Photocatalysis

Chemists have long aspired to synthesize molecules the way that plants do-using sunlight to facilitate the construction of complex molecular architectures. Nevertheless, the use of visible light in photochemical synthesis is fundamentally challenging because organic molecules tend not to interact with the wavelengths of visible light that are most strongly emitted in the solar spectrum. Recent research has begun to leverage the ability of visible light-absorbing transition metal complexes to catalyze a broad range of synthetically valuable reactions. In this review, we highlight how an understanding of the mechanisms of photocatalytic activation available to these transition metal complexes, and of the general reactivity patterns of the intermediates accessible via visible light photocatalysis, has accelerated the development of this diverse suite of reactions.

Bacterial imaging with photostable upconversion fluorescent nanoparticles

Autofluorescence, photodamage and photobleaching are often encountered when using downconverting fluorophores and fluorescent proteins for bacteria labeling. These caveats represent a serious limitation when trying to map bacteria dissemination for prolonged periods. Upconversion nanoparticles (UCNs), which are able to convert low energy near-infrared (NIR) excitation light into higher energy visible or NIR light, can address these limitations. These particles' unique optical properties translate into attractive advantages of minimal autofluorescence, reduced photodamage, deeper tissue penetration and prolonged photostability. Here, we report a UCN-based bacteria labeling strategy using Escherichia coli as prototypic bacteria. A comparative analysis highlighted the superior photostability of UCN-labeled bacteria over green fluorescent protein-expressing bacteria. Infection study of UCN-labeled bacteria in dendritic cells indicated co-localization of the UCN signal with bacterial position for up to 6 h post-infection. Furthermore, long-term monitoring of the same infected cells demonstrated the potential to utilize photostable UCN-based imaging for bacterial trafficking purposes.

Modification effects of meso-hexakis(pentafluorophenyl) [26]hexaphyrin aggregates on the photocatalytic water splitting.

Water splitting activity of a GaN:ZnO photocatalyst was improved by meso-hexakis(pentafluorophenyl) [26]hexaphyrin (3). The hexaphyrin (3) assisted the water splitting reaction over the GaN:ZnO photocatalyst by using visible light energy around 600 nm.

Direct Photocatalysis by Plasmonic Nanostructures

Recent reports have shown that plasmonic nanostructures can be used to drive direct photocatalysis with visible photons, where nanostructures act as the light absorber and the catalytic active site. These reports have showcased direct plasmon driven photocatalysis as a route to concentrate and channel the energy of low intensity visible light into adsorbed molecules, enhancing the rates of chemical transformations, and offering pathways to control reaction selectivity. In this perspective, we will discuss the fundamental photophysics of localized surface plasmon resonance (LSPR) excitation in the context of driving chemical transformations. The various demonstrated chemical conversions executed using direct plasmonic photocatalysis will be reviewed. Experimental observations, such as the dependence of photocatalytic rate on illumination intensity and photon energy, will be related to microscopic mechanisms of photocatalysis. In addition, theoretical treatments of various mechanisms within the process of d...

Carbon coated nitrogen doped P25 for the photocatalytic removal of organic pollutants under solar and low energy visible light irradiations

The commercially available TiO2 Degussa P25 was modified using a simple technique to produce a visible light active carbon (C) coated and nitrogen (N) doped P25. The modified photocatalyst was prepared by mechanical mixing of P25 powder with various amount of urea and followed by thermal heating under semi-closed reactor at different temperatures. The results showed that a layer of carbon graphite was deposited on the surface of P25 and N atoms were incorporated into the lattice of the nano-scaled photocatalyst. It was observed that the UV–Vis spectra of the modified photocatalyst exhibited red shift to the visible region as compared to that of the pristine P25, implying the decreased of band gap energy for the modified photocatalyst. Moreover, the modified photocatalyst was found to yield efficient photocatalytic degradations of the RR4, MB and phenol pollutants under visible light and solar light irradiations.

Relative Unidirectional Translation in an Artificial Molecular Assembly Fueled by Light

Motor molecules present in nature convert energy inputs, such as a chemical fuel or incident photons of light, into directed motion and force biochemical systems away from thermal equilibrium. The ability not only to control relative movements of components in molecules but also to drive their components preferentially in one direction relative to each other using versatile stimuli is one of the keys to future technological applications. Herein, we describe a wholly synthetic small-molecule system that, under the influence of chemical reagents, electrical potential, or visible light, undergoes unidirectional relative translational motion. Altering the redox state of a cyclobis(paraquat-p-phenylene) ring simultaneously (i) inverts the relative heights of kinetic barriers presented by the two termini--one a neutral 2-isopropylphenyl group and the other a positively charged 3,5-dimethylpyridinium unit--of a constitutionally asymmetric dumbbell, which can impair the threading/dethreading of a [2]pseudorotaxane, and (ii) controls the ring's affinity for a 1,5-dioxynaphthalene binding site located in the dumbbell's central core. The formation and subsequent dissociation of the [2]pseudorotaxane by passage of the ring over the neutral and positively charged termini of the dumbbell component in one, and only one, direction relatively defined has been demonstrated by (i) spectroscopic ((1)H NMR and UV/vis) means and cyclic voltammetry as well as with (ii) DFT calculations and by (iii) comparison with control compounds in the shape of constitutionally symmetrical [2]pseudorotaxanes, one with two positively charged ends and the other with two neutral ends. The operation of the system relies solely on reversible, yet stable, noncovalent bonding interactions. Moreover, in the presence of a photosensitizer, visible-light energy is the only fuel source that is needed to drive the unidirectional molecular translation, making it feasible to repeat the operation numerous times without the buildup of byproducts.

Photocatalysis by 3,6-Disubstituted-s-Tetrazine: Visible-Light Driven Metal-Free Green Synthesis of 2-Substituted Benzimidazole and Benzothiazole

s-Tetrazine based molecules were prepared for visible-light-driven organic transformations. The 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) derivative shows visible light absorption and reversible one-electron reduction behavior. In the presence of pytz and aerial oxygen, aldehyde reacts with o-phenylenediamine or o-aminothiophenol under visible light irradiation at ambient temperature to produce corresponding 2-substituted benzimidazoles and benzothiazoles, respectively. Pytz catalyst demonstrates excellent catalytic activity for alkyl, aryl, organo-metallic substituted aldehydes and reducing sugar. The reaction yield is high for both the electron-donating and electron withdrawing substituents in aromatic aldehydes. The use of a metal-free catalyst and visible light energy, along with the mild reaction conditions, makes this reaction an environmentally benign and energy-saving chemical process.