Ultrafast Photoinduced Charge Separation in Wide-Band-Capturing Self-Assembled Supramolecular Bis(donor styryl)BODIPY-Fullerene Conjugates.

A new series of self-assembled supramolecular donor-acceptor conjugates capable of wide-band capture, and exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques as artificial photosynthetic mimics. The donor host systems comprise of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) containing a crown ether entity at the meso-position and two styryl entities on the pyrrole rings. The styryl end groups also carried additional donor (triphenylamine or phenothiazine) entities. The acceptor host system was a fulleropyrrolidine comprised of an ethylammonium cation. Owing to the presence of extended conjugation and multiple chromophore entities, the BODIPY host revealed absorbance and emission well into the near-IR region covering the 300-850 nm spectral range. The donor-acceptor conjugates formed by crown ether-alkyl ammonium cation binding of the host-guest system was characterized by optical absorbance and emission, computational, and electrochemical techniques. Experimentally determined binding constants were in the range of 1-2×10(5) M(-1) . An energy-level diagram to visualize different photochemical events was established using redox, computational, absorbance, and emission data. Spectral evidence for the occurrence of photoinduced charge separation in these conjugates was established from femtosecond transient absorption studies. The measured rates indicated ultrafast charge separation and relatively slow charge recombination revealing their usefulness in light-energy harvesting and optoelectronic device applications. The bis(donor styryl)BODIPY-derived conjugates populated their triplet excited states during charge recombination.