Protolytic Photodissociation and Proton-Induced Quenching of 1-Naphthol and 2-Octadecyl-1-Naphthol in Micelles

Abstract

Kinetics of excited-state proton-transfer reactions and proton-induced fluorescence quenching of 1-naphthol (1N) and 2-octadecyl-1-naphthol (2O1N) in micellar solutions of cetyltrimethylammonium bromide (CTAB), polyoxyethylene(23) lauryl ether (Brij 35), and sodium dodecyl sulfate (SDS) was studied by using stationary and time-resolved fluorescence techniques. The ground-state acidity constant of 2O1N in cationic micelles of CTAB was found to be significantly smaller than that of the parent compound (ΔpK = 0.5). However, similar rate and equilibrium constants of the protolytic dissociation were obtained for 1N and 2O1N in the singlet excited state. Effects of nonionic micelles of Brij 35 closely resemble those of CTAB. In anionic micelles of SDS, the protolytic photodissociation was much slower for 2O1N than for 1N. The protonation rate for the excited anions in micellar solutions increases by approximately 2 orders of magnitude in the series CTAB, Brij 35, SDS. Excited-state kinetics was rationalized within the framework of a pseudophase model, which included micellar effects on the proton-transfer equilibrium and interfacial diffusion of hydronium ions. The electrostatic surface potential of charged micelles was estimated from the acidity constants of naphthols.

Conformationally Locked Chromophores as Models of Excited-State Proton Transfer in Fluorescent Proteins

“…Both ground- and excited-state proton transfer data are presented. Solid line is a fitting curve described in ref .…”

“…Analysis of the fluorescence decay curves of R*OH and R*O − in water resulted in an apparent dissociation rate constant k ESPT = 0.45 1/ns. 25 In the past, one of us 26 has analyzed the relationship between the kinetics and the thermodynamics of proton transfer from various hydroxyaromatic compounds in both the ground and excited states. All data were fitted by the unified Brønsted-type equation (Figure 4).…”

6-Hydroxyquinoline-N-oxides: A New Class of “Super” Photoacids1

“…The protolytic dissociation rate of N -oxides in MW is faster than 2.5 × 10 10 s -1 . From the known correlation between dissociation rate and equilibrium constant of various photoacids one can estimate that p K a * of N -oxides should be less than zero. Therefore the observed transition with apparent p K a * around 2.6 ( 6HQNO ) and 2.9 ( MeHQNO ) in MW is not the result of R*OH ↔ R*O - + H + equilibrium.…”

Quantification of Excited-State Brønsted–Lowry Acidity of Weak Photoacids Using Steady-State Photoluminescence Spectroscopy and a Driving-Force-Dependent Kinetic Theory

“…51−55 Nonlinear free energy relationships based on the semiempirical Rehm−Weller model for excited-state electrontransfer reactions, 56 which include a steady-state approximation, 52 have been applied to analyze data for ground-state and excited-state proton-transfer reactions between photoacids and water. 57 Analogous semiempirical models for proton transfer, developed by Marcus and Cohen, 58,59 Agmon and Levine, 60,61 Arnaut and Formosinho, 62 and Kiefer and Hynes, 63,64 20,27,64−69,29,30,38,45−49 Each of these studies utilized ultrafast spectroscopy to quantify rate constants for ESPT, and in no cases were weak photoacids studied. While these techniques should be applicable to weak photoacids, the unique aspect of our work is that through use of relatively straightforward and common steady-state photoluminescence spectroscopy, coupled to well-known processes for interpreting excited-state electron-transfer dynamics, we were able to accurately quantify the pK a * of a weak photoacid based on analysis of its excited-state proton-transfer dynamics.…”