Observation of Intensity Redistribution of Emission Peaks in Anthracene: Dynamics of Vibronic Excimer Formation in a Xerogel Matrix

Anthracene, like many other polycyclic aromatic hydrocarbons (PAHs), suffers aggregation-induced (AIQ) quenching of emission at high concentrations. This work addresses this limitation; the emission intensity of anthracene was augmented by incorporation within a cholesteryl-based xerogel matrix. The overall absolute photoluminescence quantum yield (PLQY) of concentrated anthracene xerogel (CAX) is enhanced by more than two times over the full spectrum (390–650 nm). This supramolecular host encapsulates anthracene with high density, promoting aggregation while simultaneously alleviating long-wavelength AIQ. Time-resolved emission measurements indicate that monomeric emission decays more rapidly at elevated concentrations within the blue spectral region, whereas red-shifted emission decays at a slower rate. Despite aggregation, the emission spectrum sustains its distinctive vibronic structure. Notably, time-resolved emission spectra exhibit a dynamic redistribution of intensity among vibronic features, culminating in a highly structured excimer band between 475–650 nm, which is a rarity among PAHs. Two varieties of isoenergic excimers are identified: static and dynamic. Excitation of anthracene within aggregates can directly induce excimer emission (static excimer), while an excited monomer interacting with a neighboring monomer in the ground state results in excimer formation in approximately 0.25 ns (dynamic excimer). This structured excimer emission underscores the potential of the xerogel host–guest system to enhance the vibronic resolution of excimer emission and overall fluorescence efficiency. The findings offer critical insights into excited-state dynamics within confined supramolecular environments and propose a strategy for optimizing PAH-based optoelectronic materials.