Visible Light Excitation Research Articles

C(sp3)-H Ritter amination by excitation of in situ generated iodine(III)-BF3 complexes.

Visible light excitation of iodine(III)-BF3 complex enables the formation of carbocations from C(sp3)-H bonds. The complexes are generated catalytically from iodoarene, carboxylate ligand, the oxidizing agent Selectfluor, and the Lewis acid BF3. This modular catalytic system allows the formation of synthetically valuable amine derivatives without a metal- or photocatalyst.

Decarboxylative cross-nucleophile coupling via ligand-to-metal charge transfer photoexcitation of Cu(II) carboxylates.

Reactions that enable carbon-nitrogen, carbon-oxygen and carbon-carbon bond formation lie at the heart of synthetic chemistry. However, substrate prefunctionalization is often needed to effect such transformations without forcing reaction conditions. The development of direct coupling methods for abundant feedstock chemicals is therefore highly desirable for the rapid construction of complex molecular scaffolds. Here we report a copper-mediated, net-oxidative decarboxylative coupling of carboxylic acids with diverse nucleophiles under visible-light irradiation. Preliminary mechanistic studies suggest that the relevant chromophore in this reaction is a Cu(II) carboxylate species assembled in situ. We propose that visible-light excitation to a ligand-to-metal charge transfer (LMCT) state results in a radical decarboxylation process that initiates the oxidative cross-coupling. The reaction is applicable to a wide variety of coupling partners, including complex drug molecules, suggesting that this strategy for cross-nucleophile coupling would facilitate rapid compound library synthesis for the discovery of new pharmaceutical agents.

Ratiometric fluorescent detection of lead ions in aquatic environment and living cells using a fluorescent peptide-based probe

Ratiometric fluorescent detection using dual emission bands is highly necessary to quantify Pb(II) in aquatic environment and live cells. We synthesized a ratiometric fluorescent peptidyl probe (1) by conjugation of a peptide receptor for Pb(II) with an excimer-forming benzothiazolylcyanovinylene fluorophore. The peptidyl probe dissolved well in aqueous solution and displayed an emission band at 538 nm (λex = 460 nm). Upon addition of Pb(II) (0–20 μM), the emission maximum shifted from 538 nm to 575 nm and the emission intensity ratio (I575 /I538) increased significantly from 0.40 to 2.26. 1 exhibited a selective ratiometric response to Pb(II) over other metal ions. 1 with a low detection limit (1.2 ppb) of Pb(II) detected nanomolar concentrations (0–500 nM) of Pb(II) ions in groundwater and tap water. The cell-permeable probe detected intracellular Pb(II) by ratiometric fluorescent images. The binding mode study using NMR, IR and CD spectroscopy, and TEM revealed that the probe formed a 1:1 complex with Pb(II) and then formed red-emissive nanoparticles and fibrils. The probe exhibited desirable detection properties such as ratiometric detection, high solubility in water, visible light excitation, high selectivity and sensitivity for Pb(II), cell-permeability, and rapid response (< 6 min).

Novel degradation of amoxicillin by WO3/Ag3VO4 Z-scheme heterojunction deposited on rGO

In this work, Ag3VO4 was successfully hybridized with WO3 to form Ag3VO4/WO3 (AW) Z scheme heterojunction. Then, rGO was used as a substrate for deposition of the synthesized AW to further improve its electron-hole separation efficiency and surface area. The synthesized AW deposited on rGO (AW/rGO) was used for degradation residual amoxicillin upon visible light excitation. The synthesized samples were deeply characterized by XRD, HR-TEM, BET, UV–Vis, PL and Mott–Schottky plots. Scavenger experiments were also conducted to investigate photocatalytic mechanism. The obtained results indicated well hybridizing and matching band potentials between Ag3VO4 and WO3. Thus, the photo-excited electrons (e−) at WO3 conduction band (CB) would be transported from boundary to Ag3VO4 valence band (VB) and combined with its holes (h+) to inhibit charge recombination in each material resulting in accumulation of huge amounts of available e− at Ag3VO4 CB and h+ in WO3 VB. The generated e− and h+, which were high redox potentials, effectively participated in degradation of amoxicillin. The used rGO effectively increased surface area for amoxicillin adsorption and electron transfer for charge separation of the AW. Thus, the synthesized AW/rGO sample exhibited novel amoxicillin photocatalytic degradation. Finally, the regenerating experiment results indicated novel recycling ability of the AW/rGO photocatalyst.

Interfacial charge transfer complex between TiO2 and non-aromatic ligand squaric acid

The attachment of squaric acid, a non-aromatic molecule, to the surface of TiO2 powder induced the optical absorption of the obtained hybrid material in the visible spectral range due to the interfacial charge transfer complex formation. The optical characterization of the hybrid is supported by the density functional theory calculations of the model cluster. The paramagnetic species generated upon excitation with ultraviolet or visible light, in both TiO2 powders, pristine and surface-modified, were identified conducting low-temperature solid-state and indirect electron paramagnetic resonance (EPR) spectroscopy experiments (spin trapping and spin scavenging). The solid-state EPR experiments indicated the promotion of electrons from the organic moiety to the titania conduction band under visible-light excitation of hybrid. Also, the spin scavenging experiments showed that the electrons generated in the hybrid upon the visible-light activation facilitate the reduction of the radical cations present in the dispersion, while these effects are not observed for pristine TiO2.

Cover Feature: UV Excitation of Carotenoid Binding Proteins OCP and HCP: Excited‐State Dynamics and Product Formation (ChemPhotoChem 1/2022)

The Cover Feature shows the carotenoid canthaxanthin (top) that is bound to orange carotenoid protein (OCP) and helical carotenoid protein (HCP) complexes depicted in the background of the orange (OCP) and purple (HCP) graphs. The transient absorption spectra obtained after visible-light (green) or UV-light (black) excitations demonstrate the different responses of the bound carotenoid to visible and UV light. Cover design by Cheryl Kerfeld and Tomáš Polívka. More information can be found in the Article by Tomáš Polívka and co-workers.

Ruthenium (II) Complexes Bearing Heteroleptic Terpyridine Ligands: Synthesis, Photophysics and Solar Energy Conversion

AbstractHeteroleptic ruthenium (II) complexes featuring donor functionalized phenyl‐terpyridine (ph‐tpy) and a monocarboxylic‐(ph‐tpy)/(tpy) are synthesized and characterized. Reactions of ruthenium (II) precursors at 80 °C favored heteroleptic complexes formation over the homoleptic side products. Visible light excitation of these complexes resulted in the metal‐to‐ligand charge transfer (MLCT) transitions. The inter‐planar torsional angle between the atoms of donor functionalized phenyl ring and the central pyridine (py) of the tpy core strongly influences visible light absorption and photovoltaic properties. The lower inter‐ring py‐ph torsion in the acceptor end of the MLCT structures and its increase in the oxidized doublets could prevent the back electron transfer. The ruthenium atom and the acceptor functionalized tpy host the triplet‐MLCT spin density. Ambient temperature excited‐state decay followed the energy gap law and occurred in the order of a few nanoseconds. Herein, we evaluate the photosensitizing ability of these complexes via a combined experimental and computational approach.

A Bipolar CdS/Pd Photocatalytic Membrane for Selective Segregation of Reduction and Oxidation Processes.

A photocatalytically active bipolar membrane consisting of a CdS photocatalyst and Pd electrocatalyst has been constructed to carry out environmentally relevant oxidation and reduction processes. The ion exchange property of a bipolar membrane (BPM) has allowed us to load the CdS photocatalyst on one side and Pd electrocatalyst on the other side. By inserting the photocatalytic BPM-CdS/Pd membrane between the two compartments of an H-cell, we can separate the reduction and oxidation processes. Following visible light excitation of CdS in the BPM-CdS/Pd membrane, we can induce vectorial electron transfer from CdS to Pd and to an electron acceptor (4-nitrophenol). The holes generated at CdS are scavenged by ethanol or 4-chlorophenol. The photocatalytic reduction rate dependence on the Pd loading in the membrane as well as its effect on modulating the rates of electron and hole transfer processes are discussed. The design of a semiconductor and metal loaded membrane paves the way for improving selectivity and efficiency of photocatalytic processes.

Photocatalytic Ammonia Synthesis: Mechanistic Insights into N2 Activation at Oxygen Vacancies under Visible Light Excitation

Photocatalytic Ammonia Synthesis: Mechanistic Insights into N₂ Activation at Oxygen Vacancies under Visible Light Excitation

The Photocatalyst-Free Cross-Dehydrogenative Coupling Reaction Enabled by Visible-Light Direct Excitation of Substrate.

A new photocatalyst-free strategy for the cross-dehydrogenative C-C and C-P coupling reaction has been described. This protocol provides a concise method to synthesize various 1-substituted tetrahydroisoquinoline (THIQ) derivatives enabled by visible-light direct excitation of substrates without using any photocatalyst. Moreover, a wide substrate scope demonstrated good synthetic versatility and practicality.

Ultraefficient Terahertz Emission Mediated by Shift-Current Photovoltaic Effect in Layered Gallium Telluride.

Generating terahertz waves using thin-layered materials holds great potential for the realization of integrated terahertz devices. However, previous studies have been limited by restricted radiation intensity and finite efficiency. Exploiting materials with higher efficiency for terahertz emission has attracted increasing interest worldwide. Herein, with visible-light excitation, a thin-layered GaTe film is demonstrated to be a promising emitter of terahertz radiation induced by the shift-current photovoltaic effect. Through theoretical calculations, a transient charge-transfer process resulting from the asymmetric structure of GaTe is shown to be the origin of an ultrafast shift current. Furthermore, it was found that the amplitude of the resulting terahertz signals can be manipulated by both the fluence of the pump laser and the orientation of the sample. Such high emission efficiency from the shift current indicates that the layered material (GaTe) is an excellent candidate for photovoltaics and terahertz emitters.

Synthesis of TiO 2 Using Calotropis gigantea for Visible Light Excitation and Degradation of Congo Red Dye

Green synthesized TiO2 (CG-TiO2) was prepared from Titanium isopropoxide (TTIP) precursor using aqueous leaf extract of Calotropis gigantea (CG). The CG-TiO2 was prepared with different mixing ratios of CG and TTIP varying from 1:3 to 1:5 and at different synthesis conditions, that is, mixing time, temperature, and calcination temperature. Morphological analysis indicated spherical nanoparticle clusters of CG-TiO2 with particles of an average size of 42 nm. The study indicated visible light excitation of CG-TiO2 and effective removal of Congo red from aqueous solution under visible light irradiation. A maximum Congo red removal efficiency of 97% was obtained within 2 h under the following conditions: Sample B (30 g leaves in 100 mL distilled water boiled for 2 h at 90°C); TTIP:CG – 1:3; mixing time and temperature – 2 h and 27°C, respectively; calcination temperature – 300°C.

Aligned TiO2 nanorod arrays decorated with closely interconnected Au/Ag nanoparticles: Near-infrared SERS active sensor for monitoring of antibiotic molecules in water

Near-infrared (NIR) excited surface-enhanced Raman scattering (SERS) spectroscopy is expected to have more appealing multiple-features than that of traditional ultraviolet (UV) or visible light excitation. Herein, we demonstrate an interesting and highly active hybrid semiconductor-based NIR-SERS sensor via well-aligned TiO2 nanorod arrays (NRAs) decorated with bimetallic Au/Ag nanoparticles (NPs). The obtained Au/Ag NPs-TiO2 NRAs with a stronger absorption capacity in 400–1300 nm region exhibit a remarkable higher NIR-SERS activity than that of monometallic Au or Ag loaded on TiO2 NRAs. Then, the established NIR-SERS sensor can provide ultrasensitive 785 nm laser excited-SERS detection of antibiotic ciprofloxacin and chloramphenicol in real-world water samples with detection limits as low as 10–9 M and 10–8 M, respectively. Interestingly, superior to the present bare metallic nanosubstrates, the Au/Ag NPs-TiO2 NRAs with unique heterostructures can also be served as reusable NIR-SERS sensor due to its excellent photocatalytic degradation ability, and ~84.2% residual SERS activity can be maintained after 5 recycling tests. Therefore, it is believed that the established multifunctional NIR-SERS sensor holds greater potential for ultrasensitive monitoring of diverse biomolecules in many specific applications.

Oxygen vacancy mediated charge transfer expediting over GQDs/TiO2 for enhancing photocatalytic removal of Cr (VI) and RhB synchronously

Understanding the underlying transport mechanism of photogenerated carriers is crucial in designing active heterojunctions in the field of photocatalysis. In this study, the redox activity of Graphene quantum dots/TiO2 (GQDs/TiO2) hybrid was investigated through water treatment under visible light irradiation. The corresponding findings showed that the charge transfer between GQDs and TiO2 accompanied with oxygen vacancy (Vo) was expedited, resulting in enhanced redox activity in the Cr (VI) and RhB co-removing system. Further investigation revealed that Vo introduced a defect level in TiO2 just below its conduction band that could induce visible light excitation while leading to quick charge separation and effective transmission from GQDs to TiO2. Therefore, carrying out photocatalytic Cr (VI) reduction and RhB degradation synchronously over GQDs/TiO2 can roughly enhance 2 and 3 times pure TiO2 nanosheets under visible light irradiation. The findings of this study may provide novel insight into heterojunction engineering and defect level controlling in order to attain efficient photocatalyst and offer additional prospects for photocatalytic applications.

An enhanced photoelectrochemical biosensor for colitoxin DNA based on HKUST-1/TiO2 and derived HKUST-CuO/TiO2 heterogeneous composites.

HKUST-1 MOFs and its derivative HKUST-CuO were coupled with TiO2 nanoparticles to form the heterogeneous composites of HKUST-1/TiO2 and HKUST-CuO/TiO2 based on their well-suitable bandgap energies (Eg). Compared with mono-component HKUST-1 or HKUST-CuO, theprepared composites displayed photoelectrochemical(PEC) response due to the synergistic effect from their heterogeneous structure. Higherphotocurrent response was obtained on HKUST-CuO/TiO2-modified ITO electrode (HKUST-CuO/TiO2/ITO), which could be attributed to the hollow structure with a thin shell of HKUST-CuO greatly enhancing visible spectra harvesting. The CuO component in HKUST-CuO not only could accelerate electron transfer on the heterojunction interface but also effectively separate the photo-generated charge carriers (e-1/h+). Based on the excellent PEC performance of prepared photoactive composite material, under visible-light excitation (λ ≥ 420nm) and with a working potential of 0V (vs. Ag/AgCl), the S1 (probe DNA)/HKUST-CuO/TiO2/ITO PEC platform was successfully fabricated for colitoxin DNA detection without using ascorbic acid (AA) as an electron donor. Compared with the analysis results on S1/HKUST-1/TiO2/ITO electrode, S1/HKUST-CuO/TiO2/ITO displayed a wider linear response range from 1.0 × 10-6 to 4.0 × 10-1nM with a lower detection limit of 3.73 × 10-7nM (S/N = 3), the linear regression equation was ΔI (10-6 A) =0.5549-0.1858 log (CS2/M), which confirmed the HKUST-CuO could improvesensitivity because of its prominent PEC property. The relative standard deviation (RSD) of the PEC sensor for target DNA detection of 2.0 × 10-4nM was 7.4%. The proposed DNA biosensor also possessed good specificity and stability. Hence, this reported work was a promising strategy for molecular diagnosis in the bio-analysis field. (A) Schematic illustration of the preparation process of the proposed PEC biosensors for colitoxin DNA detection. (B) The preparation process of HKUST-1 and HKUST-CuO.

Near infrared autofluorescence imaging of retinal pigmented epithelial cells using 663 nm excitation.

Fundus autofluorescence (AF) using adaptive optics scanning laser ophthalmoscopy (AOSLO) enables morphometric analysis of individual retinal pigmented epithelial (RPE) cells. However, only a few excitation wavelengths in the visible and near-infrared have been evaluated. Visible light excitation (<600 nm) presents additional safety hazards and is uncomfortable for patients. Near-infrared excitation (>700 nm) overcomes those problems but introduces others, including decreased AF signal and cone signatures that obscure RPE structure. Here we investigated the use of an intermediate wavelength, 663 nm, for excitation and compared it to 795 nm. Subjects were imaged using AOSLO equipped with a detection channel to collect AF emission between 814 and 850 nm. Two light sources (663 and 795 nm) were used to excite the retinal fluorophores. We recorded 90 s videos and registered them with custom software to integrate AF images for analysis. We imaged healthy eyes and an eye with pattern dystrophy. Similar AF microstructures were detected with each excitation source, despite ~4 times lower excitation power with 663 nm. The signal-to-noise values showed no meaningful difference between 663 nm and 795 nm excitation and a similar trend was observed for image contrast between the two excitation wavelengths. Lower light levels can be used with shorter wavelength excitation to achieve comparable images of the microstructure of the RPE as have been obtained using higher light levels at longer wavelengths. Further experiments are needed to fully characterize AF across spectrum and determine the optimal excitation and emission bandwidths that balance efficiency, patient comfort, and efficacy.

Conjugated Coordination Porphyrin-based Nanozymes for Photo-/Sono-Augmented Biocatalytic and Homologous Tumor Treatments.

Porphyrin-based nanozymes (Porzymes) have shown promising application potential to fight against tumors using catalytically generated reactive oxygen species from the excessively produced H2O2 in the tumor microenvironment. However, the low coordination porphyrin (CP) loading ratio, difficult controllable nanostructure, low bioavailability, and low biocatalytic activities of current established Porzymes have severely limited their antitumor applications. Here, a novel malignant melanoma cell membrane-coated Pd-based CP nanoplatform (Trojan Porzymes) has been synthesized for biocatalytic and homologous tumor therapies. The Trojan Porzymes exhibit a high CP loading ratio, uniform nanoscale size, single-atom nanostructure, homologous targeted ability, and high-efficiency photo/sono-augmented biocatalytic activities. The enzyme-like biocatalytic experiments display that the Trojan Porzymes can generate abundant •OH via chemodynamic path and 1O2 via visible light or ultrasound excitation. Then we demonstrate that the Trojan Porzymes show homologous targeting ability to tumor cells and can achieve efficient accumulation and long-term retention in cancer tissues. Our in vivo data further disclose that the photo/sono-assisted chemodynamic therapies can significantly augment the treatment efficiency of malignant melanoma. We believe that our work will afford a new biocatalytic and homologous strategy for future clinical malignant melanoma treatments, which may inspire and guide more future studies to develop individualized biomedicine in precise tumor therapies.

Microneedle patch based on molecular motor as a spatio-temporal controllable dosing strategy of L-DOPA for Parkinson’s disease

Controlling medication according to the condition has become a universal treatment regimen for Parkinson's disease (PD) worldwide. However, the general oral administration method is prone to a variety of digestive system discomfort, easy to be broken down by digestive juices and intestinal microorganisms, resulting in low absorption efficiency, and a serious delay in the efficacy of the drug. Here, we developed a microneedle patch (MNP) that could release drugs with controlled temporal and spatial precision triggered by near-infrared (NIR) light for the treatment of PD. The microneedles (MNs) took Gelatin-methacryloy (GelMA) as the matrix, and therapeutic drugs (L-DOPA) were stored in the mesopore of the upconversion micron-rods (UCMRs), dispersing in the GelMA. The molecular motor, as a poreblocker and gate switch, isomerizes under the excitation of ultraviolet and visible light from UCMRs for controlling drug release. This kind of MNP penetrates the epidermis in a painless, non-invasive, and non-infectious way. Under the exposure of NIR light, the L-DOPA in the MNs will be released as needed, and then it seeps into the blood and brain for relieving the symptoms of PD. In the treatment of Parkinson's mice model, this regimen significantly restored motor function, and further mechanistic studies revealed that it reduced neuroinflammation and dopaminergic neuronal death in the substantia nigra. Besides, the released L-DOPA directly entered the blood, which reduces the side effects on the gastrointestinal tract and improves the utilization rate of the drug. These attractive superiorities indicated that the MNP with controlled drug delivery system may be candidate strategies for the treatment of PD and can be used in various related biomedical fields.

A Novel Polyaniline Nanofiber Combined with Toluidine Blue as a Sensitive Detection Platform for Lignin by Raman Spectroscopy

Raman spectroscopy is widely applied in wood science because of its features of being nondestructive, rapidity, and high resolution. However, Raman scattering is weak, and the Raman signal is easily disturbed by autofluorescence arising from endogenous fluorescent molecules in biological tissue. In this work, a sensitive lignin detection platform was fabricated by a composite with a polyaniline (PANI) nanofiber and toluidine blue (TB) under the excitation of visible light. In this platform, TB acts as a specific marker for lignin, and a PANI nanofiber was used as a reinforcing reagent to improve the Raman intensity of TB. When wood slice is impregnated with TB/PANI, the lignin in wood can be precisely labeled with the TB, and the Raman intensity of TB had a threefold increase at 532 nm excitation. This TB/PANI detection platform is expected to make a significant contribution in qualitative and quantitative analysis of lignin to avoid autofluorescence in various lignin-based biosciences.

Gold anchoring to CuFe2F8(H2O)2 oxyfluoride for robust sono-photodegradation of Rhodamine-B

This work presents mixed-anion blends (e.g., oxynitrides and oxysulfides) as prospective representatives for visible-light sono-photocatalyst. While generally tolerate oxidative degradation of photogenerated holes causes to medium durability and stability. Hence, an exceptionally stable, mixed-anion oxyfluoride photocatalyst was designed and prepared based on CuFe2F8(H2O)2, decorated by gold nanoparticles (Au-NPs) as a sink for photogenerated electron and sacrificial electron mediator. Electrochemical analysis revealed Au-NPs can appearance Schottky barriers with CuFe2F8(H2O)2, injection of electrons into CuFe2F8(H2O)2, cause to electron capturing at profound surface pitfall states of CuFe2F8(H2O)2. Au-NPs sensitized CuFe2F8(H2O)2 were applied as a robust photocatalyst in pairs with ultrasound (US) waves for Rhodamine B (RhB) dye degradation. Quenching investigations indicated that •OH and •O2− were productive species for RhB degradation on Au/CuFeF8(H2O)2 which the kinetics of it was the first order and fitted to the Langmuir-Hinshelwood model. This study displays the first type of sonophotocatalytic decomposition (SPD) of an organic dye driven by visible-light excitation of a metal-doped oxyfluoride with Schottky barrier and surface plasmonic resonance (SPR).