From quenched to superradiant emission: Temperature-induced molecular rearrangement in an anthracene containing statistical copolymer

We have measured the photoluminescence spectra of an anthracene-containing statistical copolymer, AnE-PV stat. Our results reveal a striking evolution of the pure electronic transition, from its complete absence at 77 K to a superradiant emission dominating at room temperature. This transition in emission pattern is attributed to a molecular rearrangement from H-aggregate formation at 77 K to J-aggregate formation at room temperature, characterized by excitonic bandwidths of 0.18 eV and 0.26 eV, respectively. We introduce a simple model incorporating the role of temperature in modulating intermolecular coupling via molecular displacement. This model elucidates how temperature governs both the magnitude and sign of dipole-dipole molecular interactions. A modified Franck-Condon analysis is employed to quantify the intermolecular coupling, excitonic bandwidth, and the number of coherently interacting molecules responsible for superradiance. Our findings reveal coherent interactions among approximately three molecules. These insights underscore the fundamental influence of thermal effects on the photophysical properties of molecular assemblies, offering a quantitative framework for controlling excitonic behavior in conjugated systems through temperature-induced aggregation.