title: A spectroscopic study of the excited state proton transfer processes of (8-bromo-7-hydroxyquinolin-2-yl)methyl-protected phenol in aqueous solutions.
abstract: A combination of spectroscopic methods and density functional theory (DFT) computations was used to study the excited state proton transfer (ESPT) processes of (8-bromo-7-hydroxyquinolin-2-yl)methyl-protected phenol (BHQ-OPh). Characterization of the prototropic forms of BHQ-OPh in different solvent environments revealed that the neutral form predominates in acetonitrile and in 1 : 1 acetonitrile/water (pH 5.0), whereas the anionic form predominates in 1 : 1 acetonitrile/PBS (pH 7.4). Both the neutral and anionic forms were significantly populated in 1 : 1 acetonitrile/water. Upon irradiation in acetonitrile the triplet neutral form was observed, whereas the triplet anionic form was detected in 1 : 1 acetonitrile/PBS (pH 7.4). The existence of the triplet tautomeric form of BHQ-OPh in both 1 : 1 acetonitrile/water and 1 : 1 acetonitrile/water (pH 5.0), and the ESPT processes from the neutral to the anionic to the tautomeric forms in the excited state were observed using time-resolved spectroscopy. A reaction mechanism in 1 : 1 acetonitrile/water and 1 : 1 acetonitrile/water (pH 5.0) was proposed based on the spectroscopic and DFT computational results. A comparison of the results for BHQ-OPh with those of BHQ-OAc reveals that the initial prototropic states and photochemical processes are similar. The understanding gained of the initial photo-induced processes of BHQ-based photoremovable protecting groups (PPGs) is useful for the design of new quinolinyl-based PPGs for specialized applications.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China. phillips@hku.hk.
authors.forename: Jinqing
authors.initials: J
authors.lastname: Huang
authors.forename: Adna P
authors.initials: AP
authors.lastname: Muliawan
authors.forename: Jiani
authors.initials: J
authors.lastname: Ma
authors.forename: Ming De
authors.initials: M
authors.lastname: Li
authors.forename: Hoi Kei
authors.initials: HK
authors.lastname: Chiu
authors.forename: Xin
authors.initials: X
authors.lastname: Lan
authors.forename: Davide
authors.initials: D
authors.lastname: Deodato
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Dore