Photocatalytic water splitting into hydrogen is considered as a promising approach for solar energy storage. The existing organic semiconductor photocatalysts are mainly dominated by π-conjugated covalent structures featuring π → π* electronic transition. Recent studies found that activating n → π* electronic transition is an effective strategy for improving photocatalytic activity of organic semiconductors. Nevertheless, n → π* electronic transition is generally forbidden in perfect symmetric structures. Herein, we have successfully synthesized asymmetric trithiocyanuric acid (TA) aggregates by a solvent chemistry strategy. The asymmetric degrees of TA aggregates can be greatly tuned by changing the pulling strength of solvent molecules. The asymmetric characteristic of TA aggregates increases the orbital overlap between the lone pair electrons on sulfur atoms and the adjacent π* orbitals of triazine, thus allowing n → π* electronic transition. Simultaneously, the asymmetric aggregation induces a large dipole moment, significantly improving the separation and transfer of charge carriers. After an assay of a hydrogen evolution reaction, a quantum yield of 42.9 % at 400 nm was recorded for the asymmetric TA aggregates, which is much higher than those of most existing covalent semiconductors. This study unlocks a fresh realm of artificial photosynthesis, which uses asymmetric aggregates featuring n → π* electronic transition for efficient photocatalytic hydrogen production.

中文翻译：

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受控不对称聚集促进 n → π* 电子跃迁和电荷分离，增强光催化氢合成

光催化水分解成氢气被认为是太阳能存储的一种有前途的方法。现有的有机半导体光催化剂主要以π共价结构为主，具有π→π*电子跃迁。最近的研究发现，激活n→π*电子跃迁是提高有机半导体光催化活性的有效策略。然而，在完美的对称结构中，n → π* 电子跃迁通常是被禁止的。在这里，我们通过溶剂化学策略成功合成了不对称三硫氰尿酸（TA）聚集体。通过改变溶剂分子的拉伸强度可以极大地调节TA聚集体的不对称程度。 TA聚集体的不对称特性增加了硫原子上的孤对电子与三嗪相邻π*轨道之间的轨道重叠，从而允许n→π*电子跃迁。同时，不对称聚集产生大的偶极矩，显着改善载流子的分离和转移。经过析氢反应分析后，不对称 TA 聚集体在 400 nm 处记录到了 42.9% 的量子产率，远高于大多数现有共价半导体的量子产率。这项研究开启了人工光合作用的新领域，它利用具有 n → π* 电子跃迁的不对称聚集体来高效光催化制氢。