This work reports the enhancement of 23000 and 9200 times of the 15N nuclear spin polarization of cis and trans isomers of azobenzene, correspondingly, as compared to the thermal NMR signals at 9.4 T by exploiting Signal Amplification by Reversible Exchange (SABRE) and parahydrogen molecules at 400 nT simultaneously with light irradiation. Only cis-azobenzene gains substantial hyperpolarization of its 15N spins directly from parahydrogen in SABRE through the coherent polarization transfer. Consequently cis-trans photoisomerization at ultralow magnetic field preserves the SABRE-derived nuclear hyperpolarization of cis-azobenzene resulting in hyperpolarization of trans-azobenzene as well, despite its direct coordination with the SABRE Ir-complex being sterically hindered. Moreover, the proposed approach, which we called photo-SABRE, allows to hyperpolarize the long-lived spin order of trans-isomer 15N spins with a lifetime of about 25 minutes, which greatly exceeds their relaxation times at high (10 seconds) and low (200 seconds) magnetic field. Since this spin order in 15N2-trans-azobenzene is collectively formed by nuclei of different kinds, it can be detected by both 15N or 1H NMR.

In this Review, we highlight cucurbituril-based host–guest assemblies demonstrating fluorescence (singlet–singlet, FRET) and phosphorescence (triplet–singlet, TS-FRET) resonance energy transfer. We overview the achievements and challenges as well as discuss current and future applications of the cucurbituril-based energy transfer systems.

Abstract

Supramolecular systems demonstrating resonance energy transfer have recently became a topical area on the borderline of supramolecular chemistry, photochemistry, photophysics and biology. The modularity of supramolecular interactions is a prerequisite for fine tuning of optical properties, which is difficult to achieve by other means. As a component of such systems, cucurbit[n]uril (CB[n]) macrocycles can play a wide spectrum of roles from anchoring of FRET pairs and modulation of the optical output to providing biocompatibility of FRET stains for cell imaging. The aim of this Review is to outline the development of the CB[n]-based systems with fluorescence (FRET) and phosphorescence (TS-FRET) energy transfer and to highlight achievements, challenges and perspectives of this fascinating combination of a classical photophysical process and a classical supramolecular host. Particular attention in this Review is given to the current and potential applications of the reviewed systems.

This Review provides an overview on recent research on BiVO₄ heterojunction photoanodes for photoelectrochemical water oxidation reactions, including interface junction formation (Type I/Type II heterojunctions, p–n heterojunctions, Z-scheme and S-scheme heterojunctions) and surface functional junction formation (incorporating metal(oxy) hydroxides/metal oxides, functional interlayer structures, MOF/COF-based cocatalysts, molecular metal complexes, and protective layers).heterojunctioninterfacephotocatalysisphotoelectrodevanadateswater splitting

Abstract

Photoelectrochemical (PEC) water splitting has attracted strong interest as sustainable technology by converting solar energy into hydrogen. The semiconductor photoelectrodes play an important role to increase the solar-to-hydrogen conversion efficiency. Bismuth vanadate (BiVO₄) is an excellent candidate as a photoanode material for PEC water oxidation because of its visible light absorption, suitable band edge location, high stability and low cost. However, BiVO₄ alone may undergo short carrier diffusion length, rapid recombination of photo-induced charge carriers and photocorrosion. The heterojunction strategy established by combining two or more materials has provided an outstanding technique to address these issues. This Review focuses on recent important works with respect to BiVO₄ heterojunction photoanodes for PEC water oxidation reactions, including interface junction and surface functional junction formation. Additionally, challenges faced and prospects for future research on BiVO₄ heterojunction photoanodes in the field of solar-to-hydrogen conversion are proposed.

This study investigates the synthesis and catalytic performance of MA₃Sb₂I₉, a perovskite-like material, in the presence of platinum (Pt) as a co-catalyst, for hydrogen production. The material showed an enhanced hydrogen evolution performance up to 883 μmol g⁻¹ upon addition of Pt nanoparticles due to generation of additional Fermi levels in the catalytic system, and demonstrated good stability over four consecutive catalytic cycles.

Abstract

With increasing energy demands and environment concerns, the substitution of lead hybrid perovskites with antimony-based perovskite structures is an important research topic. Herein we report the synthesis of a lead-free perovskite-like material MA₃Sb₂I₉ by a hydrothermal method and the photocatalytic performance of the material in the hydrogen evolution reaction (HER). The synthesized material MA₃Sb₂I₉ has been characterized by PXRD, SEM, EDX and UV-Vis absorption spectroscopy. The band gap of the synthesized material was observed to be 2.28 eV. MA₃Sb₂I₉ demonstrated good catalytic performance for the splitting of HI using hypophosphorous acid (H₃PO₂) as scavenger. For enhancing the rate of hydrogen evolution, platinum nanoparticles have been used as a co-catalyst in different ratios. The hydrogen evolution performance of MA₃Sb₂I₉ enhanced up to 883 μmol g⁻¹ upon addition of 3 mg of Pt nanoparticles due to generation of additional Fermi levels in the catalytic system. The MA₃Sb₂I₉ material demonstrated good stability showing no evident reduction in catalytic activity after four consecutive cycles.

Surface plasmon resonance results in fascinating optical and physical characteristics when interacting with light. This Review summarized recent progress in plasmon-induced water splitting by plasmonic metal–semiconductor catalysts, including developments in the understanding of plasmonic charge separation, distribution and reaction sites, together with devices for enhancing the plasmon-induced water splitting efficiency.

Abstract

Surface plasmon resonance (SPR) in metals results in unique optical properties and photoelectric functions, which are helpful for light harvesting in photocatalysis. Additionally, the plasmon-associated charge transfer process gives a complementary platform to understand the charge dynamics at a fundamental level. This Review focused on the recent developments of water splitting by plasmonic metals/semiconductor photocatalysts. Firstly, the basic characteristics of SPR and the plasmon-enhanced photocatalysis mechanisms including plasmon resonance energy transfer and interfacial charge transfer are introduced, highlighting the recent understanding of the plasmonic electron-hole separation, distribution, and the reaction sites for water splitting. Then, advances in the strategies to improve the quantum efficiency of plasmon-induced water splitting are summarized by considering modulation in metals, interface contacts, and bulk properties of semiconductors. Finally, we discuss future prospects in the development of high-efficiency plasmonic metal/semiconductor photocatalysts for water splitting.

Organic molecules AN9P and AN2P exhibit fast reversible fluorescence evolutions upon alternate acid and base stimuli in solutions and as crystals.

Abstract

Organic compounds that can respond to external stimuli and exhibit fluorescence changes have drawn increasing attention recently because of their potential applications in intelligent displays, optical data storage, anticounterfeiting, bioimaging, and sensors. Herein, we have synthesized two new organic compounds based on frameworks of anthracene and pyridine groups: 4-(anthracen-9-yl) pyridine (AN9P) and 4-(anthracen-2-yl) pyridine (AN2P). Both compounds, in solution and solid state, including polycrystals and single crystals, display reversible fluorescence transformations under alternate acid and base treatments. AN9P and AN2P solutions could be regulated to emit white-light luminescence. The photoluminescence of the AN9P and AN2P polycrystals showed fast fluorescence changes with wide ranges (>300 nm) upon alternate acid and base stimuli and still exhibited remarkable fluorescence emission with almost no attenuation after 15 cycles of the reversible process. Both experimental and computational results suggested that the heteroatom nitrogen in the AN9P and AN2P molecules significantly influenced the intra- and intermolecular electronic interactions during the reversible protonation and deprotonation processes, resulting in changes in their frontier molecular orbitals and fluorescence emission characteristics. Our results provide a new facile approach to design molecular structures that realize highly dynamic photoluminescence changes in both liquid solution and solid crystal.

The identification and quantification of hydrogen (H)-bonded complexes form the cornerstone of reaction-mechanism analysis in ultrafast proton transfers. Traditionally, the Benesi-Hildebrand method has been employed to obtain the formation constants of H-bonded complexes, given that H-bonding additives induce an alteration in spectral features exclusively through H-bond formation. However, if the additive introduction impacts the bulk polarity of the solution, inducing a spectral shift, the spectroscopic method's accuracy in analyzing the H-bond formation becomes compromised. In this study, we scrutinize H-bond formation under the influence of an H-bond accepting solute in an aprotic solvent. This is achieved by quantifying the fractions of two concurrent pathways involved in the excited-state proton transfer (ESPT) of a super-photoacid: the ultrafast ESPT of an H-bonded complex vs. the diffusion-controlled ESPT of the free acid. Our method offers improved accuracy compared to conventional steady-state spectroscopic techniques, by directly quantifying the H-bonded complexes using the time-resolved spectroscopic method, thereby circumventing the aforementioned limitation.

New complex [RuLCl2(PPh3)] (L= N,N-bis(2-hydroxy-5-nitrobenzaldehyde)-2,2’-diaminodiethylamine) was prepared and characterized analytically. [RuLCl2(PPh3)] was employed as a luminescent chemosensor for the detection of anions. The results show that [RuLCl2(PPh3)] can detect HSO4 ̄ and AcO ̄ selectively with sequential order in H2O-CH3CN (8:2, v/v) at pH 7.0. The spectral binding, titration, and interference analyses reveal that the addition of HSO4 ̄ to [RuLCl2(PPh3)] emits a distinguished fluorescence intensity (IF/I0= 6.55) significantly. This shows that HSO4 ̄ interacts suitably with the complex to switch ON the fluorescence which could be explained by inhibition of a PET mechanism as the above addition forms [RuLCl(HSO4)(PPh3)] in the excited state. Selectivity of [RuLCl2(PPh3)] with HSO4 ̄ forms [RuLCl(HSO4)(PPh3)] in the water showing a negligible change in its emission except for AcO ̄, which enhances fluorescence intensity. For the addition of AcO ̄  to [RuLCl2(PPh3)] forms [RuLCl(AcO)(PPh3)], however, the adding of HSO4 ̄  to [RuLCl(AcO)(PPh3)] does not show any change in the intensity, suggesting that there exists a logic gate function for the addition of HSO4 ̄  followed by AcO ̄  to [RuLCl2(PPh3)]. This finding is interesting because [RuLCl2(PPh3)] can act as a fast selective chemosensor for the sequential detection of HSO4 ̄ and AcO ̄.

Asymmetric boron complexes composed of (iso)quinolyl-pyrrole ligands possessing triphenylamine unit on the (iso)quinoline or pyrrole moieties were systematically prepared. Their optical properties were investigated in various organic solvents, and they showed solvatochromic properties, which were influenced by the π-structure of the ligands and the position of the electron-donor group. The degrees of changes in the emission-color drastically changed for regioisomeric chromophores 1 and 2. In this study, the solvatochromic properties of the compounds were investigated and described using both experimental and computational results.

Touching base: The photobasicity and pH sensitivity of a fluorescent indolin-3-imine derivative is described. The fluorophore can deprotonate and sense weakly acidic protic solvents – a process enhanced by excited state proton transfer. Cell imaging experiments revealed that indolin-3-imine is a potential scaffold for fluorescence cell microscopy.

Abstract

This work presents the pH sensing ability of a fluorescent indolin-3-imine derivative. Protonation of the weakly basic imine (pK _a=8.3 of its conjugate acid) results in a significant red-shift of the absorption band. The fluorophore acts as a photobase, with a basicity increase of approximately 6 units upon photoexcitation. This behavior promotes excited state proton transfer from weak acids such as protic solvents. The characteristics of the fluorophore enable sensing of water fractions in organic solvents and differentiation between methanol, ethanol, and longer chain alcohols. Initial cell studies indicated the future potential of indolin-3-imines as fluorophores for bioimaging applications.