Light-harvesting with panchromatically absorbing BODIPY–porphyrazine conjugates to power electron transfer in supramolecular donor–acceptor ensembles

Abstract

Prerequisites for the design of efficient organic solar light converting systems are intense absorptions across the visible region, the ability to funnel excited state energy by intramolecular energy transfer, and the option to partake in photoinduced electron transfer processes. We have established a versatile synthesis platform for functionalized porphyrazines and present the synthesis of a light harvesting dibenzoquinoxalinoporphyrazine that is peripherally substituted with eight alkynyl-linked BODIPY chromophores. Photophysical investigation by means of time-resolved fluorescence and femtosecond transient absorption spectroscopy revealed efficient intramolecular energy transfer from the photoexcited BODIPY to the porphyrazine core. Coordination of a pyridyl-functionalized phenothiazine (PTZ) to the central metal ion of the porphyrazine generates a complex capable of an efficient electron transfer from the PTZ to the photoexcited porphyrazine core. The porphyrazine˙⁻/PTZ˙⁺ fingerprints in the visible and in the near-infrared regions as well as the electron transfer dynamics were determined using spectroelectrochemistry and femtosecond transient absorption spectroscopy. The findings form the basis for the development of supramolecular multichromophore ensembles as materials in solar light converting systems.