Spectroscopic investigation on the effect of pairing anions in imidazolium-based ionic liquids on the J-aggregation of meso-tetrakis-(4-sulfonatophenyl)porphyrin in aqueous solution

► TPPS is used as the spectroscopic probe to study solvent effect of ionic liquids. ► TPPS shows different spectroscopic behaviors in BMIMBF4 and BMIMTS aqueous solution. ► Cations in BMIMBF4 initially promote J-aggregation of TPPS and then break it. ► π-π and hydrophobic interactions between TS− and TPPS mainly inhibit J-aggregation.