Micellization Turned on Dual Fluorescence and Room Temperature Phosphorescence by Pseudo-ESIPT in Thiadiazole Derivatives

Abstract

Some luminophores cannot fluoresce from dilute solution, especially those that are highly flexible. By aggregation, the rigidity of these molecules increases allowing for photoluminescence. However, the enhanced rigidity and the intermolecular interactions can give rise to several high-energy excited states, and since they can fluoresce only from the lowest energy excited state, known as the Kasha rule, the energy surplus is lost to the surroundings. In the pursuit of developing efficient light harvesting strategies from the higher energy excited states, it is necessary to look upon the effects not only at the level of nanometric molecules themselves but also of their supramolecular assemblies. Herein, we pinpoint the impact of poor conjugated moieties over the chromophore units, as well as the optical phenomena emerging at the supramolecular level. The molecular design consists of the S-alkylation of 5-amino-1,3,4-thiadiazole-2-thiol with permethylated silicone or hydrocarbons. The synthesized compounds display excited state intermolecular proton transfer (pseudo-ESIPT), blue and green fluorescence, and near-infrared phosphorescence at room temperature.