In a photo-energy conversion system, the efficiency of photon capture is one of key issues that determine the overall efficiency. Metal nanostructures are recently drawing attention due to their unique optical properties, which are known as localized surface plasmon resonance (LSPR). Since metal nanostructures can confine incoming photon energy into the nanoscale region through excitation of LSPR, they are expected to function as optical nano-antennas. Indeed, various optical processes such as Raman scattering or fluorescence can gain intensity from LSPR. Such plasmonic enhancement is theoretically well explained and various applications have been demonstrated. On the other hand, plasmonic enhancement of photochemical reactions is still under discussion because the efficiency of photochemical reactions is influenced by many factors. Moreover, kinetics of photochemical reactions may be much slower than the lifetime of LSPR; plasmonic effect is not straightforward in this case. We have reported that photo-induced uphill single-electron transfer reaction can be enhanced by forming plsmonic nano-antennas on top of porphyrin-linked molecular monolayers at an Au electrode. In this talk, plasmonic enhancement of multi-electron transfer reactions will also be discussed, which are governed by more complicated and slower kinetics.

Fig. local field enhancement near an Au nanoparticle deposited on molecular monolayer on an Au substrate