Molecular Dipole-Induced Photoredox Catalysis for Hydrogen Evolution over Self-Assembled Naphthalimide Nanoribbons.

ABSTRACT

D-π-A type 4-((9-phenylcarbazol-3-yl)ethynyl)-N-dodecyl-1,8-naphthalimide (CZNI) with a large dipole moment of 8.49 D and A-π-A type bis[(4,4'-1,8-naphthalimide)-N-dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of a molecular dipole as the dominant mechanism for controlling charge separation of organic semiconductors. In aqueous solution, these two novel naphthalimides can self-assemble to form nanoribbons (NRs) that present significantly different traces of exciton dissociation dynamics. Upon photoexcitation of NINI-NRs, no charge-separated excitons (CSEs) are formed due to the large exciton binding energy, accordingly there is no hydrogen evolution. On the contrary, in the photoexcited CZNI-NRs, the initial bound Frenkel excitons are dissociated to long-lived CSEs after undergoing ultrafast charge transfer within ca. 1.25 ps and charge separation within less than 5.0 ps. Finally, these free electrons were injected into Pt co-catalysts for reducing protons to H2 at a rate of ca. 417 µmol h-1 g-1 , correspondingly an apparent quantum efficiency of ca. 1.3 % can be achieved at 400 nm.