Engineering Donor-Acceptor Arrangement in Perylene Diimide-Based Covalent Organic Frameworks for Enhanced Singlet...

The photocatalytic efficiency of two-dimensional covalent organic frameworks (2D COFs) is governed by the spatial arrangement of donor-acceptor (D-A) moieties, which strongly influences exciton transport. However, precise control over D-A alignment, especially across intra- and interlayer dimensions, remains a key challenge for optimizing singlet oxygen (¹O₂) generation. Here, we present a linker geometry-directed approach to modulate D-A organization within perylene diimide (PDI)-based COFs. Two imine-linked 2D COFs, PDI-TPE-COF and PDI-DBC-COF, were synthesized by condensing a PDI acceptor with either a flexible tetraphenylethylene (TPE) or a rigid dibenzo[g,p]chrysene (DBC) donor. While PDI-TPE-COF adopts an eclipsed AA stacking, the rigid DBC linker induces an inclined AB stacking in PDI-DBC-COF, promoting both inter- and intralayer exciton migration. Both COFs exhibit quantitative ¹O₂ generation under visible light irradiation, but PDI-DBC-COF delivers a 42% higher quantum yield. This leads to markedly enhanced photocatalytic activity in quinoxaline and α-aminocarbonyl synthesis under low-intensity LED light. Transient absorption (TA) studies and theoretical calculations confirm the key role of interlayer exciton transfer. PDI-DBC-COF also shows excellent recyclability and gram-scale applicability under simulated sunlight. This work highlights the critical role of spatial D-A engineering in exciton control and offers design principles for high-performance, metal-free COF photocatalysts.