Axially Assembled Photosynthetic Antenna-Reaction Center Mimics Composed of Boron Dipyrromethenes, Aluminum Porphyrin, and Fullerene Derivatives

Abstract

Sequential photoinduced energy transfer followed by electron transfer leading to the formation of charge separated states in a newly assembled series of supramolecular triads comprised of boron dipyrromethenes (BODIPY or BDP), aluminum porphyrin (AlTPP) and C₆₀ is demonstrated. In the present strategy, the energy donor (BDP) and electron acceptor (C₆₀) were axially positioned to the plane of AlTPP via the central metal. The structural integrity of the newly synthesized compounds and self-assembled systems were fully established using spectral, electrochemical and computational methods. Thermodynamic feasibility of energy transfer from ¹BDP* to AlTPP and subsequent electron transfer from ¹AlTPP* to generate BDP-AlTPP^•+-C₆₀^•- charge separated states was derived from free-energy calculations. Occurrence of ultrafast energy transfer from ¹BDP* to AlTPP was established from studies involving steady-state and time-resolved emission, as well as femtosecond transient spectroscopic techniques. The BDP-AlTPP^•+-C₆₀^•- charge separated states persisted for several nanoseconds prior returning to the ground state.