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 (C60 ), 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-C60 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 (1) BODIPY* were realized from the energy-level diagram. Accordingly, (1) BODIPY* resulted in competitive ultrafast energy transfer to produce BODIPY-(1) azaBODIPY*-C60 and electron transfer to produce BODIPY(.) (+) -azaBODIPY-C60 (.) (-) as major photochemical events. The charge-separated state persisted for few nanoseconds prior populating (3) C60 *, 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.