Strongly Coupled Oxasmaragdyrin-BF2 Chelated Dipyrrin Dyads: Syntheses, X-ray Structure, Ground- and Excited-State Charge-Transfer Interactions.

Abstract

Oxasmaragdyrin (osm), a 22-π electron aromatic macrocycle containing four pyrroles and a furan ring connected by three methine bridges and two direct bonds is shown to be an excellent electron donor-sensitizer exhibiting adequate spectral and redox properties. Further, this novel heterocyclic macromolecule has been utilized in building donor-acceptor systems involving BF2 -chelated dipyrromethenes (BODIPYs). The osm-BODIPY dyads were fully characterized by optical, electrochemical, computational, and X-ray diffraction studies. Due to close proximity and electronic structure of the donor and acceptor entities, strong intramolecular charge-transfer interactions in these dyads was witnessed and was supported by computational studies. Solvent-polarity-dependent rapid charge separation and charge recombination in these dyads is witnessed from photochemical studies involving time-resolved emission and femtosecond transient absorption studies. The present studies bring out the importance of oxasmaragdyrin as an electron donor in light-energy-harvesting artificial photosynthesis model systems.