Features of the decay of excited states of ionic dyes in the near field of metal nanoparticles

Abstract

The influence factor of silver nanoparticles on the intramolecular processes of deactivation of the electronically excited state of polymethine dyes (PD) of different ionicity has been studied. It has been demonstrated that the optical density for cationic 1 and anionic 2 dyes does not change under the action of the plasmon field of Ag nanoparticles. Whereas an increase in absorbance by almost 18% was observed for neutral dye 3. A decrease in the enhancement in fluorescence intensity in the series of anionic–cationic–neutral dyes was registered upon addition of Ag nanoparticles to their solutions. The fluorescence lifetime practically does not change for all PDs under study. Data processing within the framework of the model of the influence of a plasmonic nanoparticle on radiative transitions in a dye molecule showed that the values of plasmon-enhanced rates of radiative decay of molecules decreases from neutral to cationic and, finally, to anionic dye. The rates of energy transfer from PD to plasmonic nanoparticles decrease in the reverse sequence of dyes, i.e. anionic-cationic-neutral PD. This is expressed in a decrease in the proportion of neutral dye molecules that were deactivated by fluorescence.