Pure and Applied Chemistry

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.