Multistep Energy and Electron Transfer in a "V-Configured" Supramolecular BODIPY-azaBODIPY-Fullerene Triad: Mimicry of Photosynthetic Antenna Reaction-Center Events

A new photosynthetic antenna-reaction-center model compound composed of covalently linked BF2-chelated dipyrromethene (BODIPY), BF2-chelated azadipyrromethene (azaBODIPY), and fullerene (C-60), in a V-configuration, has been newly synthesized and characterized by using a multistep synthetic procedure. Optical absorbance and steady-state fluorescence, computational, and electrochemical studies were systematically performed in nonpolar, toluene, and polar, benzonitrile, solvents to establish the molecular integrity of the triad and to construct an energy-level diagram revealing different photochemical events. The geometry obtained by B3LYP/6-31G* calculations revealed the anticipated V-configuration of the BODIPY-azaBODIPY-C-60 triad. The location of the frontier orbitals in the triad tracked the site of electron transfer determined from electrochemical studies. The different photochemical events originated from (BODIPY)-B-1* were realized from the energy-level diagram. Accordingly, (BODIPY)-B-1* resulted in competitive ultrafast energy transfer to produce BODIPY-(1)azaBODIPY*-C-60 and electron transfer to produce BODIPY.+-azaBODIPY-C-60(.-) as major photochemical events. The charge-separated state persisted for few nanoseconds prior populating C-3(60)*, which in turn revealed an unusual triplet-triplet energy transfer to produce (3)azaBODIPY* prior returning to the ground state. These findings delineate the importance of multimodular systems in energy harvesting, and more importantly, their utility in building multifunction performing optoelectronic devices.