Plasmon–molecular resonance coupling: Chlorine-p6 adsorbed on poly-l-lysine stabilized silver nanoparticles

Plasmon–molecular resonance coupling between Chlorine-p6 (Cp6) and poly-l-lysine stabilized silver nanoparticles (pLL-AgNP), both of which absorbs strongly at 400 nm, is reported. Resonance coupling results in a decrease in the intensity of the 400 nm band accompanied by a splitting. Coupling decreases at low pH due to partial neutralization of the charge of Cp6. The fluorescence intensity of Cp6 at pH 7 in the presence of pLL-AgNP gets drastically reduced which is attributed to the formation of non-fluorescent coupled states. The effect of only the polymer (poly-l-lysine) was also investigated. Spectroscopic studies suggest that polymer induces significant aggregation of Cp6 by electrostatic interaction.