Artificial photosynthetic antenna-reaction center complexes based on a hexaphenylbenzene core

Abstract

A hexaphenylbenzene scaffold has been used to organize the components of artificial photosynthetic antennas and antenna-reaction center mimics that feature bis(phenylethynyl)anthracene antenna moieties and porphyrin-fullerene charge-separation units. The five bis(phenylethynyl)anthracene chromophores absorb in the spectral region around 430-480 nm, where porphyrins have low extinction coefficients but solar irradiance is maximal. The hexaphenylbenzene core was built up by the well-known Diels-Alder reaction of diarylacetylenes with substituted tetraphenylcyclopentadienones. The latter were in turn prepared by condensation of substituted benzils and dibenzyl ketones, allowing flexibility in the design of the substitution pattern on the core. The spacing between the various chromophores is suitable for rapid singlet-singlet energy transfer among antenna moieties and the porphyrin, and the relatively rigid structure of the hexaphenylbenzene limits conformational heterogeneity that could reduce the efficiency of energy and electron transfer. NMR studies reveal a high barrier to rotation of the porphyirn plane relative to the hexaphenylbenzene.