2- naphthol fluorescence lifetime

The pK of tyrosine explains the absence of measurable excited-state proton transfer in water. The pK is the negative logarithm of the ratio of the deprotonation and the bimolecular reprotonation rates. Since reprotonation is diffusion-controlled, this rate will be the same for tyrosine and 2-naphthol. The difference of nearly two in their respective pK values means that the excited-state deprotonation rate of tyrosine is nearly two orders of magnitude slower than that of 2-naphthol.(26) This means that the rate of excited-state proton transfer by tyrosine to water is on the order of 105s 1. With a fluorescence lifetime near 3 ns for tyrosine, the combined rates for radiative and nonradiative processes approach 109s-1. Thus, the proton transfer reaction is too slow to compete effectively with the other deactivation pathways. 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

Fluorescence Lifetime of Free and Bound 2-Naphthol-3,6-Disulfonate... 

Table 2 ) has value similar to homogeneous aqueous solution [5, 6, 7]. This fact gives evidence that the photodissociation rate is limited by the proton transfer step ( but not by the diffusion of excited molecules to micellar interface ) and the reaction take place in micellar phase [8, 9]. Fluorescence lifetimes of 1-naphthol and 4-chloro-l-naphthol anions ArO are sensitive to the nature of the solvent [7, 10]. 

Proceeding of the protolytic photoreaction in lipid bilayer was proved also by the fluorescence spectra and the lifetimes of the hydroxyaromatic anions formed in the reaction, which are different from that in the aqueous solution. For example, fluorescence lifetimes of anion of 1-naphthol are 7.5 ns in water and 12.3 ns in the EL vesicles. These data indicate on the formation of ArO directly in the photoreaction inside the vesicular membrane. It is important to emphasize that fluorescence decay kinetics in the both cases is well monoexponential as at the beginning as after at least two orders of magnitude decay. In contrast to naph-tholate anions formed in the photoreaction, ArO formed in the alkaline solution of vesicles ( pH % 13 ) are localized ( both in the ground and excited singlet states ) in aqueous phase and have the same fluorescence lifetime as in aqueous solution ( Table 5 ). This means that migration of ArO formed in vesicles into aqueous phase is too slow comparatively to its lifetime. 

Chen, S., Inskeep, W.P., Williams, S.A., and Callis, P.R. (1994). Fluorescence lifetime measurements of fluyoranthene, 1-naphthol, and napropamide in the presence of dissolved humic acid. Environ. Sci. TechnoL, 28, 1582-1588. 

Fluorescence in INpOH-aliphatic amine hydrogen-bonded systems in nonpolar rigid matrices like polyethylene films at 77 K is dual in nature [200-202], The ESPT in the hydrogen-bonded complex results in two types of ion pairs, one with in-plane orientation between excited naphtholate and ammonium ions (fluorescence maximum at 395 nm with a lifetime of 5.3 nsec) and the other with an... 

The exit rate constants of the excited anions after the photoprotolytic dissociation of l,4-dichloro-2-naphthol within decylsulfate, dedecylsulfate, and cetylsulfate micelles were measured with a fluorescence quencher hardly penetrating the micelles, - the nitrate ion [121]. The addition of nitrate into the solution quenched the fluorescence of those anions which escape from the micelles within the lifetime of the excited state only. The exit rate constant of the naphtholate anion increases with increasing length of the hydrocarbon radical in the micelle-forming surfactant. The exit rate is thus controlled by the lowering of the micelle polarity (i.e. by the free energy of the exit process) rather than by the micelle size or the distance that the anion must diffuse. Perhaps one can establish a kind of correlation between the rate constant of this process and its free energy as was done for photochemical electron transfer [126] and proton transfer [156,157]. 

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