Pressure-Induced Stacking of Rhodamine 6G Molecules

Extended conjugation of molecular π systems is of great significance for solar cells and organic light-emitting diodes as these can serve as new light absorbing and emitting chromophores. This research demonstrates the potential of using pressure and a solvent environment to create larger assemblies of molecular π-conjugated systems. We selected rhodamine 6G (Rh6G) to study the pressure-induced stacking of molecules in three different solvents: methanol (MeOH), isopropanol (IPA), and a 16:3:1 mixture of methanol:ethanol:water (MEW). Absorption, emission, and fluorescence lifetime were studied at pressures of up to 11.38 GPa. We found that pressure-induced stacking mechanisms can present solvent dependence: high pressures tend to create emissive H-aggregates in MeOH and MEW, but excimers in IPA. This work guides and demonstrates routes to stacking organic molecules using high pressures and provides fundamental insights into the formation of extended conjugation π systems.