σ–π Hyperconjugation Unlocks Interlayer Charge Separation of Ullazine-Based Supramolecular Nanostructures for Photocatalytic Hydrogen Evolution
Qin Yang, Wanqing Li, Ying Wang, Yan Zhuang, Shuhong Wu, Shuo Wang, Na Wen, Zhengxin Ding, Huaxiang Lin, Jinlin Long
Abstract
This work proposes a σ–π hyperconjugation strategy to establish interlayer charge transport channels (CTC) in supramolecular organic nanostructures. A series of ullazine-based molecular semiconductors were designed and synthesized successfully by engineering end groups to demonstrate the σ–π hyperconjugation that unlocks the quantum confinement of photogenerated charges in π-conjugated planes. Ullazine grafted with tert -butyl (U- t -Bu) showed a J -cross-stacking model in which the cross-stacked U- t -Bu molecular pair smoothly glides along the elongated dimension, forming a Z-schemed interlayer CTC by σ–π hyperconjugations between C–H σ-bonds of tert -butyl end group and π-bonds of ullazines in adjacent layers along the stacking dimension. Consequently, upon photoexcitation of ullazine-based supramolecular nanoaggregates in aqueous solution, the formed Frenkel excitons are dissociated to charge-separated excitons by the interlayer charge separation channels, undergoing an ultrafast charge transfer within 0.58 ps and an ultrafast charge separation within 0.67 ps. The Z-schemed charge separation between adjacent layers leads to a significantly enhanced hydrogen yield over U- t -Bu/PVP/Pt, with a hydrogen evolution rate of 369.9 μmol·g –1 ·h –1 and an apparent quantum yield of 1.46% at 420 nm. It is 3.8-fold larger than that of ullazine modified with methoxy (U-OMe), without the σ–π hyperconjugation.