Electron and energy transfer in a porphyrin–oxoporphyrinogen–fullerene triad, ZnP–OxP–C60

Abstract

A multichromophoric triad, ZnP–OxP–C₆₀ containing porphyrin (ZnTPP hereafter ZnP), oxoporphyrinogen (OxP) and fullerene (C₆₀) has been synthesized to probe the intramolecular dynamics of its electron and energy transfer in relation to the presence of the closely linked electron deficient OxP–C₆₀ ‘special pair’, constructed as a mimic of the naturally occurring photosynthetic antenna-reaction center. The DFT optimized structure of the triad reveals the relative spatial remoteness of the ZnP entity with proximal OxP/C₆₀ entities. Free-energetics of different energy and electron transfer events were estimated using spectral, computational and electrochemical studies, according to the Rehm–Weller approach. Femtosecond transient absorption spectral studies revealed energy transfer from ¹ZnP* to OxP to yield ZnP–¹OxP*–C₆₀, and electron transfer to yield ZnP˙⁺–OxP–C₆₀˙⁻ and/or ZnP–OxP˙⁺–C₆₀˙⁻ charge seperated states. That is, the ZnP entity in the triad operates as both antenna and electron donor to generate relatively long-lived charge separated states thus mimicking the early photoevents of natural photosynthesis.