Influence of the Plasmon Effect on the Decay of Excited Electronic States of Anthracene and its Halogen-Substituted Analog.

The influence of the plasmonic fields of silver nanoparticles (Ag NP) on the photophysical properties of anthracene and its brominated analog was investigated. Through experimental and theoretical approaches, changes in quantum yields, luminescence intensities, and lifetimes are quantified. The plasmon field is shown to significantly enhance fast fluorescence, delayed fluorescence (DF), and phosphorescence, particularly for the halogen-substituted derivative 9.10-dibromanthracene (DBA). TD-DFT calculations confirm increased spin-orbit coupling (SOC) matrix elements in DBA, consistent with the observed acceleration of intersystem crossing (ISC). Furthermore, the dependence of radiative transition rates on the molecule-nanoparticle surface distance is established. These findings clarify interaction mechanisms between organic molecules and plasmonic nanostructures, offering insights for the design of luminescent and sensor materials with tunable emission characteristics.