Perylene-dispersed PVA films: Fluorescence quenching and cryogenic fluorescence color change of hydrophobic fluorophore in a wet state

In this study, we fabricated films containing hydrophobic crystalline perylene highly dispersed in a hydrophilic polyvinyl alcohol (PVA) matrix, and observed dramatic fluorescence (FL) changes due to vibronic coupling (VC) and cryogenic charge transfer between perylene and water in a wet state. Both PVA and perylene were dissolved in dimethyl sulfoxide, and films with excellent appearance and smooth surfaces were obtained from this solution by a conventional convection drying method. In a completely dry state, the films exhibited strong blue-light FL emission under ultraviolet (UV) light, which was immediately quenched when wetted with water due to VC. Even after repeating the wetting process several times, no phase separation was observed in the re-dried films, and the wavelength corresponding to the blue FL remained unchanged. When the wet film was cryogenically cooled by immersing it in liquid nitrogen, quite strong orange FL emission due to charge transfer was observed under UV light.