Solvent effects of imidazolium ionic liquids on photophysical properties of π-electron extended rhodamine dye ABPX

• The proton accepting capacity of the ionic liquid depends on their anion, which affected the formation of the dicationic form upon protonation of ABPX01. • Alkyl groups substituted for imidazolium cations caused macroscopic changes in viscosity, and contributed to the increase in fluorescence intensity and fluorescence lifetime. We studied the solvent effect of imidazolium ionic liquids, which are media with microphase separation in their structure, on the cationic dye ABPX01. The proton accepting capacity of ionic liquids differs depending on their anions. Protonation of ABPX01 was enhanced in ionic liquids composed of anions with low proton accepting capacity, resulting in an increased proportion of dicationic forms. The alkyl group of the imidazolium cation caused a macroscopic change in viscosity, leading to a slight enhancement of the fluorescence intensity and an extension of the fluorescence lifetime. ABPX has potential material applications as a probe for the proton accepting capacity of ionic liquids and as a dye with AIE properties when used with suitable ionic liquids as a medium. The solvent effect of imidazolium ionic liquids, which are media with a microphase separation in their structure, on the cationic dye ABPX01 was studied. Protonation of ABPX01 was enhanced in ionic liquids consisting of anions with low proton accepting capacity, resulting in an increased proportion of dicationic form of ABPX01. As an effect of the cationic structure of ionic liquids, the alkyl group caused a macroscopic change in viscosity and a slight increase in fluorescence intensity and fluorescence lifetime.