Resonance Raman Characterization of the Forms of Ground-State 8-Substituted 7- Hydroxyquinoline Caged Acetate Compounds in Aqueous Solutions

8-bromo-7-hydroxyquinolinyl group (BHQ) is a promising class of phototriggers with high enough sensitivity to be effective for both one-photon excitation (1PE) and two-photon excitation (2PE) applications in physiological environments. Similar to BHQ, 8-substituted 7-hydroxyquinolines, like 8-chloro-7-hydroxyquinoline (CHQ) and 8-cyano-7-hydroxyquinoline (CyHQ), are able to be useful for 1PE and 2PE and their acetate acids CHQ-OAc and CyHQ-OAc were also able to undergo photolysis reactions in neutral aqueous buffer solutions. To examine the substituent effect on the relative populations of the forms of the ground state species of 8-substituted 7-hydroxyquinolines, ultraviolet absorption and resonance Raman spectroscopy experiments were done for CHQ-OAc and CyHQ-OAc in acetonitrile (MeCN), in NaOH-H(2)O/MeCN (60:40, v/v, pH 11-12), and in H(2)O/MeCN (60:40, v/v, pH 6-7) solutions. These spectroscopic results were compared to those previously determined for the BHQ-OAc compound.