Thermal Control of Intermolecular Interactions and Tuning of Fluorescent-State Energies

The prospect of tuning the energy of emitting states through external stimuli opens the possibility of shifting the energy of emitting units on demand and controlling the bimolecular processes they are involved in. To prove this concept, the fluorescence properties of three differently 9,10-substituted anthracene (ANT) derivatives are investigated in a phase-change material (eicosane). The liquid-to-solid transition of the medium leads to an increase of the local dye concentration, a shortening of the intermolecular distances, and the establishment of excited- and ground-state interactions. As a result, a new contribution to the overall luminescence that derives from the downshifted emission (up to 0.7 eV) from excimer-like species is observed. The addition of a second dye (a Pt-porphyrin) reduces the efficiency of excited- and ground-state complexes between fluorophore units, although it does not prevent the formation of multichromophoric aggregates where interactions between Pt-porphyrin and the emissive state of ANT derivatives are observed. The emission of excimer-like species, formed upon solidification of the medium, can be exploited to further down-shift the fluorescence through energy-transfer processes to a suitable energy acceptor, such as rubrene.