The UV absorption and fluorescence spectra of 1,3-di (α-naphthyl) propane (1), di (α-naphthylmethyl) ether (2), and α-methylnaphthalene (3) in aqueous methanol, ethanol, and DMSOwere recorded as a function of Φ value (fraction of water in binary solvents). The existence of two sta-tes, a metastable state (defined as m) and a stable stationary state (defined as s), of molecules 1 as well as2 in the above cosolvents at high Φ was shown by the contrary fluorescence excimer to monomerintensity (Ie/Im)vs. Φ relationships of the samples prepared with different processes. On the basis ofthe Φ value, substrate concentration, and the temperature dependence of the UV spectra. fluores-cence excitation and emission spectra, the chromophores of 1, 2 show the formation of aggregates inground state at high Φ owing to the hydrophobic interaction. The m states consist of a supersaturatedsolution with aggregates, whereas the s states are suspended microcrystals or micro-oil-droplets withaggregates. The conformations of the molecules in the aggregates were discussed. Single crystal X-raystructure of 2 is reported. The UV absorption and fluorescence spectra of 1,3-di (α-naphthyl) propane (1), di (α-naphthylmethyl) ether (2), and α-methylnaphthalene (3) in aqueous methanol, a function of Φ value (fraction of water in binary solvents). The existence of two sta-tes, a metastable state (defined as m) and a stable stationary state (defined as s), of molecules 1 as well as 2 in the above cosolvents at high Φ was shown by the contrary fluorescence excimer to monomerintensity (Ie / Im) vs. Φ relationships of the samples prepared with different processes. On the basis ofthe Φ value, substrate concentration, and the temperature dependence of the UV spectra. fluores -cence excitation and emission spectra, the chromophores of 1, 2 show the formation of aggregates inground state at high Φ owing to the hydrophobic interaction. The m states consist of a supersaturated solution with aggregates, but the states are suspended microcrystals or micro-oil -droplets withaggregat es. The conformations of the molecules in the aggregates were discussed. Single crystal X-raystructure of 2 is reported.