2DES Reveals Ultrafast Energy Transfer in a Hybrid Bio-conjugate Bacterial Reaction Center

The photosynthetic Reaction Center (RC) from purple bacterium Rb Sphaeroides has unique photoconversion capabilities which can be ideally used to build up bio-hybrid devices for solar energy conversion. Recently, an efficient covalent functionalization of the bacterial RC with an 'ad-hoc' synthetized organic chromophore has been successfully implemented.1-3 Heptamethyne Cyanine dyes were purposely synthesized to acts as a light harvesting antenna in the visible spectral range, leading to a robust increase in ability of energy photoconversion compared to the pristine native system. We have characterized the dynamics of energy and charge transfer in this bio-conjugated RC employing 2D electronic spectroscopy (2DES). This technique has specific abilities to reveal complex patterns of energy migration and couplings among interconnected chromophores with femtosecond time resolution. Our results reveal the occurrence of ultrafast energy transfer from the light harvesting chromophore towards the special pair and the monomer bacterio-chlorophyll acting primary electron donors in the native protein, and an increased rate of charge separation with the bacterio-pheophytin electron acceptor compared to the wild type RC.