Enhanced one- and two-photon excited fluorescence of cationic (phenothiazinyl)vinyl-pyridinium chromophore attached to polyelectrolyte-coated gold nanorods

In this paper we evaluate the effect of plasmonic enhancement on the fluorescence properties of cationic (phenothiazinyl)vinyl-pyridinium (PVP) chromophore attached to polyelectrolyte-coated gold nanorods (PE-AuNRs). We provide reliable evidence for the conveniently enhancement of both one- and two-photon excited fluorescence of PVP molecules on PE-AuNRs due to their favorable entrapment away from the metallic surface via multilayer PE coating. While the enhancement under one-photon excitation is mainly ascribed to the amplification of the emission rate due to plasmon effect, the two-photon excited enhancement is believed to arise from a combination of local electric field amplification and competition between increased radiative and non-radiative decay rates. Additionally, we perform numerical simulation using Finite-Difference Time-Domain method to understand better the mechanism of fluorescence enhancement under two-photon excitation.