Cooperative dissociation of J-aggregates into monomers in the 2-isobutoxyethanol/water binary solvent with the lower critical solution temperature

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J-aggregates are supramolecular assemblies with characteristic optical properties originating from their excitonic interactions and have applications in fluorescence biosensing and artificial light-harvesting systems. Herein, we investigated the formation and dissociation of the J-aggregates of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiIC18(3)) in 2-isobutoxyethanol (iBE)/water (W) binary solvents with the lower critical solution temperature (LCST). We found that DiIC18(3) forms J-aggregates in iBE/W binary solvents with compositions of 12/88–17/83% (v/v). By measuring the temperature dependence of the absorption spectra, we found that the J-aggregates dissociate into monomers cooperatively before the iBE/W binary solvents show the liquid–liquid phase separation. The hydrophobicity of the iBE/W binary solvents was evaluated by measuring the fluorescence spectra of 1-Anilinonaphtharene-8-sulfonic acid (1,8-ANS), whose fluorescence peak wavelength reflects the hydrophobicity of the solvents. The J-aggregates were found to dissociate cooperatively when the iBE/W binary solvents reached a constant hydrophobicity, although the composition of the iBE/W binary solvents was different. The J-aggregates precipitated without dissociation in binary solvents without the LCST. We propose that concentration fluctuation of iBE/W binary solvents promotes the cooperative dissociation of the DiIC18(3) J-aggregates.