Facile non-fullerene acceptors for efficient photocatalytic hydrogen evolution

Abstract

Organic semiconducting materials generally have large exciton binding energy due to low dielectric constants, necessitating donor:acceptor interfacial charge transfer state (CTS) for effective exciton dissociation. Precisely regulating the energy levels of donors and acceptors can effectively modulate CTS energetics. In this work, we develop a strategy for decoupled regulation of molecular energy levels by enhancing short-range intramolecular charge transfer (ICT) in non-fullerene acceptors (NFAs). We design two NFAs (B-2TPIC and T-2TPIC) incorporating strong electron-donating thieno[3,2-b]pyrrole and strong electron-accepting 3-(1,1-dicyanomethylene)-5,6- difluoro-1-indanone (IC2F) units. Density functional theory calculations reveal that pronounced electron density redistribution induces strong short-range ICT between thieno[3,2-b]pyrrole and IC2F units, leading to considerable upshift of the lowest unoccupied molecular orbital (LUMO) level and small migration of the highest occupied molecular orbital (HOMO) level with decoupling HOMO/LUMO regulation. Both B-2TPIC and T-2TPIC show LUMO levels higher than −3.8 eV, HOMO levels deeper than −5.5 eV, and strong visible and near-infrared absorption. When these NFAs are blended with the polymer donor PM6 and used as photocatalysts for hydrogen evolution, the PM6:B-2TPIC nanoparticles exhibit faster hole transfer and weaker charge recombination, resulting in an average hydrogen evolution rate of 267.4 mmol g−1 h−1 at a low concentration of 6.67 μg mL−1 for 4 h under AM 1.5 G simulated sunlight (100 mW cm−2), higher than that of the PM6:T-2TPIC counterpart (165.1 mmol g−1 h−1).