“Two-Point” Self-Assembly and Photoinduced Electron Transfer in meso-Donor-Carrying Bis(styryl crown ether)-BODIPY–Bis(alkylammonium)fullerene Donor–Acceptor Conjugates

5 years ago

“Two-Point” Self-Assembly and Photoinduced Electron Transfer in meso-Donor-Carrying Bis(styryl crown ether)-BODIPY–Bis(alkylammonium)fullerene Donor–Acceptor Conjugates

Habtom B. Gobeze, Shuai Shao, Paul A. Karr, Francis D'Souza

BF2-chelated dipyrromethene, BODIPY, was functionalized to carry two styryl crown ether tails and a secondary electron donor at the meso position. By using a “two-point” self-assembly strategy, a bis-alkylammonium-functionalized fullerene (C60) was allowed to self-assemble the crown ether voids of BODIPY to obtain multimodular donor–acceptor conjugates. As a consequence of the two-point binding, the 1:1 stoichiometric complexes formed yielded complexes of higher stability in which fluorescence of BODIPY was found to be quenched; this suggested the occurrence of excited-state processes. The geometry and electronic structure of the self-assembled complexes were derived from B3LYP/3-21G(*) methods in which no steric constraints between the entities was observed. An energy-level diagram was established by using spectral, electrochemical, and computational results to help understand the mechanistic details of excited-state processes originating from 1bis-styryl-BODIPY*. Femtosecond transient absorbance studies were indicative of the formation of an exciplex state prior to the charge-separation process to yield a bis-styryl-BODIPY.+–C60.− radical ion pair. The time constants for charge separation were generally lower than charge-recombination processes. The present studies bring out the importance of multimode binding strategies to obtain stable self-assembled donor–acceptor conjugates capable of undergoing photoinduced charge separation needed in artificial photosynthetic applications. Shining light on the matter: Formation of stable self-assembled hybrids and the occurrence of photoinduced electron transfer via an intermediate exciplex state in bis(styryl crown ether)-BODIPY–fullerene donor–acceptor conjugates is demonstrated (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/asia.201700662