Photoinduced Electron Transfer in the Strong Coupling Regime: Waveguide–Plasmon Polaritons

Reversible exchange of photons between a material and an optical cavity can lead to the formation of hybrid light–matter states where material properties such as the work function [Hutchison et al. Adv. Mater. 2013, 25, 2481−2485 ], chemical reactivity [Hutchison et al. Angew. Chem., Int. Ed. 2012, 51, 1592−1596 ], ultrafast energy relaxation [Salomon et al. Angew. Chem., Int. Ed. 2009, 48, 8748−8751 ; Gomez et al. J. Phys. Chem. B 2013, 117, 4340–4346 ], and electrical conductivity [Orgiu et al. Nat. Mater. 2015, 14, 1123−1129 ] of matter differ significantly to those of the same material in the absence of strong interactions with the electromagnetic fields. Here we show that strong light–matter coupling between confined photons on a semiconductor waveguide and localized plasmon resonances on metal nanowires modifies the efficiency of the photoinduced charge-transfer rate of plasmonic derived (hot) electrons into accepting states in the semiconductor material. Ultrafast spectroscopy measurements reveal a strong correlation between the amplitude of the transient signals, attributed to electrons residing in the semiconductor and the hybridization of waveguide and plasmon excitations.