Solvent-dependent two-photon photoluminescence and excitation dynamics of gold nanorods

Abstract

PEG-SH-capped gold nanorods (Au NRs) well dispersed in various organic solvents have been prepared to study the solvent effects on the two-photon photoluminescence (TPPL) properties and ultrafast excitation dynamics of Au NRs. The TPPL intensities of Au NRs in different organic solvents including DMF, DEG, CH3OH, C2H5OH, CH3CN, DMSO, and THF were found to be significantly quenched compared to that of Au NRs in H2O. Ultrafast time-resolved transient absorption and pump-probe measurements have been performed on Au NRs in H2O, DMF, and DEG to understand the corresponding quenching mechanisms. Different from the excitation decay behaviors of Au NRs in H2O, an additional transient species was observed in Au NRs in DMF or DEG upon photoexcitation. This intermediate state is ascribed to the charge-separated species, which serves as direct evidence to support that the observed TPPL quenching in various organic solvents is due to electron transfer from electron-donating solvents to the excited Au NRs. The charge-transfer mechanism was further supported by the observation that the TPPL intensity of Au NRs in H2O was found to be quenched by nearly 5.0-fold in the presence of S2-. These studies provide useful information on fundamental understanding of the TPPL properties as well as development of various potential biological applications of gold nanoparticles. © 2013 American Chemical Society.