Construction of oxygen-enriched graphitic carbon nitride polymers for highly efficient and selective H₂O₂ production via photocatalytic O₂ reduction.

Amine-containing polymers and small molecules with only nonconventional chromophores are found to emit strong luminescence under suitable conditions, and their oxidation products are believed to be the chromophores. However, the oxidized species or groups have never been thoroughly separated and well characterized and hence the main chromophore(s) responsible for the fluorescence is not clear. In this work, three isomeric small molecular aliphatic amines are oxidized with H₂O₂ and then their oxidized products are separated and characterized. Both primary and secondary amines can be oxidized with H₂O₂, while tertiary amines cannot. Oximes (R–CN–OH) rather than hydroxylamines are proved to be the chromophores for the first time. Hexanal oxime emits very weak fluorescence in dilute solutions, but becomes highly emissive in thick solutions or in the solid state, exhibiting distinct aggregation-induced emission (AIE) characteristics. The fluorescence of hexanal oxime is also sensitive to temperature and metal ions. Crystallographic data from the single crystal structure of hexanal oxime and theoretical calculations prove that the aggregation of oxime groups (CN–OH) through intermolecular hydrogen bonding results in extended conjugation and a rigidified conformation, which lead to strong fluorescence in the aggregated state.

Multifunctional stimuli-responsive materials with room-temperature phosphorescence (RTP) has been demonstrated to be one of the most important members of the stimuli-responsive material family and their development remains a great challenge at this stage. Herein, we successfully synthesized two coordination polymers (CPs), formulated as {[M(cbbpy)(HBTC)(H₂O)]·2H₂O}_n (M = Zn (1) and Cd (2)), using a viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy) and trimesic acid (H₃BTC) by tuning different metal ions. Complexes 1 and 2 show excellent chromic behavior in response to X-ray and UV light. In particular, complex 1 exhibits thermochromism. Moreover, complexes 1 and 2 exhibit dual fluorescence and RTP emissions in the solid state, emitting yellow afterglow of 1.5 s and 1 s at room temperature (297 K) and cyan afterglow of 6.5 s and 5 s at a low temperature (77 K), respectively, when turning off the UV lamp. A hypothetical mechanism is proposed via theoretical calculations that the fluorescence corresponds to the transfer of electrons from the viologen-based moiety to O1 and O2 of complexes. And the phosphorescence corresponds to the intersystem crossing (ISC) process with electrons being transferred from the viologen moiety through the metal atom to the carboxyl group of trimesic acid in an excited triplet state and then transition back to the ground state. In addition, multiple encryption and anti-counterfeiting were successfully designed through photochromism, fluorescence and RTP of these complexes. This work not only provides a new strategy for the design and synthesis of multifunctional materials, but also develops a new dynamic photo-controlled afterglow switching.

Despite the tremendous efforts in developing non‐fullerene acceptor (NFA) for polymer solar cells (PSCs), only few researches are done on studying the NFA molecular structure dependent stability of PSCs, and long‐term stable PSCs are only reported for the cells with low efficiency. Herein, the authors compare the stability of inverted PM6:NFA solar cells using ITIC, IT‐4F, Y6, and N3 as the NFA, and a decay rate order of IT‐4F > Y6 ≈ N3 > ITIC is measured. Quantum chemical calculations reveal that fluorine substitution weakens the C═C bond and enhances the interaction between NFA and ZnO, whereas the β‐alkyl chains on the thiophene unit next to the C═C linker blocks the attacking of hydroxyl radicals onto the C═C bonds. Knowing this, the authors choose a bulky alkyl side chain containing molecule (named L8‐BO) as the acceptor, which shows slower photo bleaching and performance decay rates. A combination of ZnO surface passivation with phenylethanethiol (PET) yields a high efficiency of 17% and an estimated long T₈₀ and Ts₈₀ of 5140 and 6170 h, respectively. The results indicate functionalization of the β‐position of the thiophene unit is an effective way to improve device stability of the NFA.