Surface Plasmons Control the Dynamics of Excited Triplet States in the Presence of Gold Nanoparticles

Aqueous gold nanoparticles (AuNPs) cause a large increase in the yield of methylene blue triplets ((MB)-M-3*) obtained upon 650 nm laser excitation as a result of surface plasmon field interactions that can be described as transmitter-receiver antenna effects. Two distinct (MB)-M-3* populations are observed; a fast decaying one (tau(T) = 25 ns) is believed to be due to molecules on the AuNP surface at the time of excitation and is described as static quenching. A longer lived (MB)-M-3* population has lifetimes in the tens of microseconds but is subject to an anomalously high rate constant for a AuNP quenching of 6.4 x 10(13) M-1 s(-1). This ultrafast quenching is attributed to a nonrandom distribution caused by the AuNP plasmon field that preferentially excites MB molecules located in the proximity of the AuNP where they are subject to antenna type interactions with the nanoparticle and are spatially predisposed for efficient quenching.