Light-driven hydrogen evolution system with glutamic-acid-modified zinc porphyrin as photosensitizer and [FeFe]-hydrogenase model as catalyst

Abstract

An intermolecular light-driven hydrogen evolution system with free glutamic-acid-modified zinc tetra(p-phenyl) porphyrin (Glu-ZnP) as a photosensitizer and [Fe2(CO)6(μ-adt)C6H5] [μ-adt = N(CH2S)2] (Badt) as a catalyst has been constructed. Using phenylmercaptan (BSH) as electron donor and acetic acid (HOAc) as proton source, hydrogen was obtained after irradiation with visible light for 2 h; the efficiency is comparable to that of the similar intramolecular dyad. Steady-state and time-resolved spectroscopy and cyclic voltammetry show that both the first and the second electron transfer from singlet 1* Glu-ZnP to Badt and reduced Badt are thermodynamically feasible. However, the competition of electron transfer from singlet 1* Glu-ZnP to Badt with intersystem crossing from singlet 1* Glu-ZnP to triplet 3* Glu-ZnP, inefficient electron transfer from triplet 3* Glu-ZnP to Badt, and the lower energy of triplet 3* Glu-ZnP and possible 3* Badt to that of yielded charge-separated state of Glu-ZnP +· -Badt −· were believed to be the obstacles for efficient hydrogen evolution.