Efficient Photoinduced Electron Transfer from Pyrene-o-Carborane Heterojunction to Selenoviologen for Enhanced Photocatalytic Hydrogen Evolution and Reduction of Alkynes

Photoinduced Radical Luminescence of Diazapyrene Derivatives upon Complexation with Cucurbit[n]uril Hosts

Molecular design with an electron donor-acceptor (D-A) structure and host-guest complexation are effective strategies for stabilizing radicals. Herein, we report the design and synthesis of cationic diazapyrene derivatives featuring a D-A structure, as well as the influence of host-guest complexation on their photoinduced organic radical photophysical properties. Compared to the methylated diazapyrene 1, the other three derivatives 2-4, containing triphenylamine, coumarin, and naphthalene units as D groups, respectively, are more favorable for the generation of radicals. Binding studies reveal that cucurbit[8]uril (CB[8]) forms 1 : 1 inclusion complexes with derivatives 2-4, while CB[10] forms a 2 : 2 inclusion complex with 2 and supramolecular polymers with 3 and 4. The radical luminescence of derivatives 1-4 in aqueous solution is significantly promoted upon complexation with CB[8] or CB[10]. Additionally, the emission color of 3 shifts from cyan to yellow-green upon light irradiation in the presence of CB[8].

A De Novo Auto-Activated Solar-Driven Biohybrid System for Hydrogen Production in Methanotrophic Cells

Climate change driving by greenhouse gas emissions from petroleum-based energy has garnered significant attention. Renewable energy production via a sustainable system that integrates the cell factory and visible-light-driven photocatalysts offers a novel approach for upcycling methane and addressing global energy challenges. Here, an auto-activated biohybrid system driven by solar energy is developed for converting methane into hydrogen fuel, which incorporated thienoviologen (S-MV2+) and genetically engineered methanotrophic bacteria. In this system, S-MV2+ functioned as photosensitizer and electron mediator, capturing solar energy and supplying electrons for an enzyme-catalyzed bioprocess. The genetically modified Methylomicrobium buryatense 5GB1 mutant, lacking methanol dehydrogenase but overexpressing hydrogenase, is able to convert methane into methanol that maintains the electron flow cycle by quenching photogenerated holes for both hydrogen biosynthesis and methane oxidation. Finally, the highest H2 production of 272.96 μM from this biohybrid system was achieved with methanol as a sacrificial agent generated by the H2-producing mutant, resulting in a 140-fold enhancement. This innovative method showcases the potential of coupling photocatalysis with methanotrophic biocatalysis for sustainable energy production. Additionally, the system introduces a new strategy for self-regeneration of sacrificial agents, offering a promising avenue for hydrogen production using greenhouse gases in an eco-friendly manner.

Directional Electron Flow in a Selenoviologen-Based Tetracationic Cyclophane for Enhanced Visible-Light-Driven Hydrogen Evolution

Directional electron flow in the photocatalyst enables efficient charge separation, which is essential for efficient photocatalysis of H2 production. Here, we report a novel class of tetracationic cyclophanes (7) incorporating bipyridine Pt(II) and selenoviologen. X-ray single-crystal structures reveal that 7 not only fixes the distances and spatial positions between its individual units but also exhibits a box-like rigid electron-deficient cavity. Moreover, host-guest recognition phenomena are observed between 7 and ferrocene, forming host-guest complexes with a 1 : 1 stoichiometry. 7 exhibits good redox properties, narrow energy gaps, and strong absorption in the visible range (370-500 nm) due to containing two selenoviologen (SeV2+) units. Meanwhile, the femtosecond transient absorption (fs-TA) reveals that 7 has stabilized dicationic biradical, efficient charge separation, and facilitates directional electron flow to achieve efficient electron transfer due to the formation of rigid cyclophane and electronic architecture. Then, 7 is applied to visible-light-driven hydrogen evolution with high hydrogen production (132 μmol), generation rate (11 μmol/h), turnover number (221), and apparent quantum yield (1.7 %), which provides a simplified and efficient photocatalytic strategy for solar energy conversion.

Cyclometalated Iridium(III) Complexes Containing Viologen-Modified Phenylpyridine Ligands as Electroluminochromic Active Molecules for Information Display

Electroluminochromic (ELC) materials have garnered significant research interest because of their potential applications in lighting, displaying, and sensing. These materials exhibit reversible modulation of photoluminescence under low-voltage stimuli. Here five phosphorescent iridium(III) complexes are reported featuring viologen-substituted 2-phenylpyridine (Vppy) ligands acting as electroactive components. Four of the complexes are bis-cyclometalated and coordinated with either neutral bipyridine derivatives or negatively charged 2-picolinate. The remaining complex is heteroleptic tris-cyclometalated, containing one Vppy and two 2-phenylquinoline ligands. Upon photoexcitation, the bis-cyclometalated complexes exhibit orange to red phosphorescence originating from mixed triplet metal-to-ligand charge transfer (3MLCT) and intraligand (3IL) dπ(Ir)/π(Vppy) → π*(Vppy) state, whereas the tris-cyclometalated complex is non-emissive due to a low Ir(IV/III) oxidation potential favoring oxidative quenching by the viologen pendants. When the cationic viologens are electrochemically reduced to their neutral form, the bis-cyclometalated complexes show a remarkable blue-shift in their phosphorescence maxima due to increased energy levels of the Vppy molecular orbitals. In the case of the tris-cyclometalated complex, reduction of the viologen groups interrupts the quenching process, leading to a luminescence turn-on. These complexes are used to develop ELC devices, which exhibit reversible luminescence response in terms of color or on-off switching under a low voltage of 2 V.

An All-In-One Integrating Strategy for Designing Platinum(II)-Based Supramolecular Polymers for Photocatalytic Hydrogen Evolution

Organic polymer photocatalysts have achieved significant progress in photocatalytic hydrogen evolution, while developing the integrated organic polymers possessing the functions of photosensitizer, electron transfer mediator, and catalyst simultaneously is urgently needed and presents a great challenge. Considering that chalcogenoviologens are able to act as photosensitizers and electron-transfer mediators, a series of chalcogenoviologen-containing platinum(II)-based supramolecular polymers is designed, which exhibited strong visible light-absorbing ability and suitable bandgap for highly efficient photocatalytic hydrogen evolution without the use of a cocatalyst. The hydrogen evolution rate (HER) increases steadily with the decrease in an optical gap of the polymer. Among these "all-in-one" polymers, Se-containing 2D porous polymer exhibited the best photocatalytic performance with a HER of 3.09 mmol g-1 h-1 under visible light (>420 nm) irradiation. Experimental and theoretical calculations reveal that the distinct intramolecular charge transfer characteristics and heteroatom N in terpyridine unit promote charge separation and transfer within the molecules. This work could provide new insights into the design of metallo-supramolecular polymers with finely tuned components for photocatalytic hydrogen evolution from water.

Synthesis, Photophysical and Electronic Properties of a D-π-A Julolidine-Like Pyrenyl-o-Carborane

We synthesized 2-(1-1,2-dicarbadodecaboranyl(12))-6,6,12,12-tetramethyl-7,8,11,12-tetrahydro-6H,10H-phenaleno[1,9-fg]pyrido[3,2,1-ij]quinoline (4), a julolidine-like pyrenyl-o-carborane, with pyrene substituted at the 2,7-positions on the HOMO/LUMO nodal plane. Using solid state molecular structures, photophysical data, cyclic voltammetry, DFT and LR-TDDFT calculations, we compare o-carborane and B(Mes)2 (Mes=2,4,6-Me3C6H2) as acceptor groups. Whereas the π-acceptor strength of B(Mes)2 is sufficient to drop the pyrene LUMO+1 below the LUMO, the carborane does not do this. We confirm the π-donor strength of the julolidine-like moiety, however, which raises the pyrene HOMO-1 above the HOMO. In contrast to the analogous pyrene-2-yl-o-carborane, 2-(1-1,2-dicarbadodecaboranyl(12))-pyrene VI, which exhibits dual fluorescence, because the rate of internal conversion between locally-excited (LE) and charge transfer (CT) (from the pyrene to the carborane) states is faster than the radiative decay rate, leading to a thermodynamic equilibrium between the 2 states, 4 shows only single fluorescence, as the CT state involving the carborane as the acceptor moiety in not kinetically accessible, so a more localized CT emission involving the julolidine-like pyrene moiety is observed.

A High-Density Raman Photometry for Tracking and Quantifying of AchE Activity in The Brain of Freely Moving Animals with Network

A high-density Raman photometry based on a dual-recognition strategy is created for accurately quantifying acetylcholinesterase (AchE) activity in 24 brain regions of free-moving animals with network. A series of 5-ethynyl-1,2,3,3-tetramethyl-based molecules with different conjugated structures and substitute groups are designed and synthesized for specific recognition of AchE by Raman spectroscopy. After systematically evaluating the recognition ability toward AchE, 2-(4-((4-(dimethylamino)benzoyl)oxy)styryl)-5-ethynyl-1,3,3-trimethyl-3H-indol-1-ium (ET-5) is finally optimized for AchE determination, which shows the highest selectivity, the greatest sensitivity, and the fastest response time among the investigated seven molecules. More interestingly, using the developed probe for AchE with high accuracy and sensitivity, the optimized AchE regulated by nitric oxide (NO) is discovered for promoting the neurogenesis of neural stem cells (NSCs). Benefiting from the high-density photometry, it is found that the activity and distribution of AchE varied in 24 brain regions, and the levels of AchE activity in 24 brain regions of Alzheimer's mice (AD) are lower than those of normal mice. It is the first time that a functional network of AchE in 24 brain regions is established. It is also found that the loss of AchE functional network in AD mice is restored and reconstructed by the controlled release of AchE regulated by NO.

Survey of Recent Advances in Molecular Fluorophores, Unconjugated Polymers, and Emerging Functional Materials Designed for Electrofluorochromic Use

In this review, recent advances that exploit the intrinsic emission of organic materials for reversibly modulating their intensity with applied potential are surveyed. Key design strategies that have been adopted during the past five years for developing such electrofluorochromic materials are presented, focusing on molecular fluorophores that are coupled with redox-active moieties, intrinsically electroactive molecular fluorophores, and unconjugated emissive organic polymers. The structural effects, main challenges, and strides toward addressing the limitations of emerging fluorescent materials that are electrochemically responsive are surveyed, along with how these can be adapted for their use in electrofluorochromic devices.

Enhanced Built-in Electric Field Promotes Photocatalytic Hydrogen Performance of Polymers Derived from the Introduction of B←N Coordination Bond

High concentrations of active carriers on the surface of a semiconductor through energy/electron transfer are the core process in the photocatalytic hydrogen production from water. However, it remains a challenge to significantly improve photocatalytic performance by modifying simple molecular modulation. Herein, a new strategy is proposed to enhance the photocatalytic hydrogen evolution performance using boron and nitrogen elements to construct B←N coordination bonds. Experimental results show that polynaphthopyridine borane (PNBN) possessing B←N coordination bonds shows a hydrogen evolution rate of 217.4 µmol h-1 , which is significantly higher than that of the comparison materials 0 µmol h-1 for polyphenylnaphthalene (PNCC) and 0.66 µmol h-1 for polypyridylnaphthalene (PNNC), mainly attributed to the formation of a strong built-in electric field that promotes the separation of photo-generated electrons/holes. This work opens up new prospects for the design of highly efficient polymeric photocatalysts at the molecular level.