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The stabilization of the ground-state keto tautomer of 7-hydroxyquinoline (7HQ) has been observed in roomtemperature methanol and aqueous solutions. Concentration studies have shown that the 7HQ cyclic dimer is formed at high 7HQ concentrations in methanol and water, and either the 7HQ-(MeOH)z or the 7HQ-water complex, presumably the cyclic 7HQ-(H20)2 structure, is formed at low 7HQ concentrations in methanol or water solvents, respectively. These species give rise to the keto-tautomer excitation band centered at 398 nm (7HQ dimer in water), 420 nm (7HQ dimer in methanol), 377 nm (7HQ-water complex), and 387 nm (7HQ-methanol complex). The emission band for all species appears at 520 nm. This is the first report of the ground-state stabilized keto tautomer spectrum in methanol at room temperature. The spectrum in water has been investigated in the past, but the interpretation differs from that of this work.

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