A functional linkage between light-harvesting and photocatalytic components is a pivotal issue for using solar energy in chemical conversions; however, this concept is far from being practically realized. Here, we constructed a system that integrates an artificially extended photosynthetic light-harvesting complex 2 (LH2) and a light-harvesting 1-reaction center (RC) core complex (LH1-RC). A biohybrid LH2, whose light-harvesting ability was extended by a covalently attached hydrophobic fluorophore ATTO647N (LH2-ATTO) to cover the absorption gap of LH2, was assembled with LH1-RC in a lipid bilayer. Femtosecond transient absorption spectroscopy revealed that upon an excitation of the ATTO, sequential excitation energy transfer (EET), ATTO → LH2 → LH1 → RC, was followed by a subsequent electron transfer in the RC with rates comparable to those in a native system. As a proof of concept, the functional linkage between light-harvesting and photocatalytic reactions was quantitatively demonstrated through the enhancement in the charge separation yield and photocurrent generation activity of LH2-ATTO/LH1-RC assembled on an electrode.

Photosynthetic light-harvesting (LH) systems consist of photosynthetic pigments, which are non-covalently self-assembled with protein scaffolds in many phototrophs and attain highly efficient excitation energy transfer via ultrafast dynamics. In this study, we constructed a biohybrid LH system composed of an LH complex (LH2) from Rhodoblastus acidophilus strain 10050 and a hydrophobic fluorophore ATTO647N (ATTO) as an extrinsic antenna in the lipid bilayer. Through the addition of ATTOs into a solution of LH2-reconstituted lipid vesicles, ATTOs were incorporated into the hydrophobic interior of the lipid bilayer to configure the non-covalently self-assembled biohybrid LH. Steady-state fluorescence spectroscopy clearly showed efficient energy transfer from ATTO to B850 bacteriochlorophylls in LH2. Femtosecond transient absorption spectroscopy revealed that the energy transfer took place in the time range of 3–13 ps, comparable to that of the covalently linked LH2-ATTO that we previously reported. In addition, the biohybrid LH system exhibited a much higher antenna effect than the LH2-ATTO system because of the higher loading level of ATTO in the membrane. These findings suggest that the facile self-assembled biohybrid LH system is a promising system for constructing LH for solar-energy conversion.