Tuning antibonding-orbital occupancy in pyrene-COFs via electron-donating phenolic −OH for boosted photocatalytic H2 evolution

Covalent organic frameworks (COFs) are widely studied as photocatalysts for the hydrogen evolution reaction (HER), yet most design strategies target light absorption or charge separation rather than the H* desorption barrier at the catalytic site itself. We re-examine the problem from a bond-resolved view: the crystal orbital Hamilton population (COHP) is used to treat the occupancy of the N−H antibonding manifold as a quantitative descriptor of how strongly the imine nitrogen of a Schiff-base COF binds H*. Two pyrene-based COFs, PY-BD and PY-DHBD, are synthesized to test the descriptor. Adding two phenolic −OH groups to the dialdehyde linker raises the antibonding occupancy (ICOHP from −7.52 to −7.18 eV), weakens the N−H bond, and shifts Δ G H* from −0.22 to 0.04 eV, close to thermoneutrality. The visible-light H 2 -evolution rate accordingly rises from 450 to 1127 μmol g −1 h −1 , 2.5-fold the rate of PY-BD. The work places COHP-resolved antibonding occupancy alongside the d -band-centre framework familiar from metal catalysis as a quantitative descriptor for tuning HER on N-rich COF active sites. Grafting electron-donating phenolic –OH groups onto a pyrene-based COF raises the N-H antibonding-orbital occupancy for photocatalytic H 2 evolution under visible light. Download: Download high-res image (149KB) Download: Download full-size image