Using carotenoid with ICT state to overcome the limit of photosynthetic light-harvesting

Abstract

The excitation energy transfer (EET) from carotenoid to bacteriochlorophyll a (Bchl a) has a significant impact in determining the overall efficiency of utilization of the incident solar spectrum of the primary process of bacterial photosynthesis. This can be enhanced when the carotenoid has intramolecular charge-transfer (ICT) character, such as in the light-harvesting systems in marine alga and diatoms. This study provides new insights into the significance of the ICT excited states following incorporation of a higher plant carotenoid, β-apo-8'-carotenal, into the carotenoidless LH1 system from the purple photosynthetic bacterium, Rhodospirillum rubrum strain G9+. β-apo-8'-carotenal generates two types of the ICT excited state in the reconstituted LH1 complex there by achieving an efficiency of EET that exceeds that found in the wild-type LH1 complex. The present study demonstrates a strategy of how to go beyond the EET efficiency from carotenoid to Bchl a, which has evolved in the bacterial light-harvesting systems.