Excited-State Proton Transfer of 1-Naphthol in Micelles

Abstract

The fast deprotonation of 1-naphthol, which occurs in 35 ps in aqueous solution, is studied in neutral (triton X 100, reduced, TX-100R), cationic (cetyl trimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles. Drastically different effects on the proton transfer process and the relative emission intensities of the neutral form (360 nm) and the anion (460 nm) are observed in the three micelles. The intensities of the anion and the neutral emission of 1-naphthol exhibit a break around the reported critical micellar concentration (cmc) of the three micelles. Above cmc, intensity of the neutral emission is enhanced by a factor of nearly 90, 66, and 20 in 20 mM TX-100R, 200 mM SDS, and 96 mM CTAB, respectively. The anion emission is enhanced for CTAB and TX-100R, while for SDS its intensity decreases, compared to water. In CTAB, the rise time of the 460 nm emission (600 ( 100 ps) is similar to the lifetime of decay at 360 nm. However, for TX-100R and SDS, the rise time of the anion emission (at 460 nm) is found to be faster than the decay of the neutral emission (at 360 nm). This indicates that in TX-100R and SDS, there is no parental relation between the normal and the anion emission and they originate from the probe, 1-naphthol molecules, at distinctly different locations. The rise times at 460 nm are 1.8 ( 0.1 ns and 600 ( 100 ps for TX-100R and SDS, respectively, while the corresponding decay times at 360 nm are 2.5 ( 0.1 ns and 1.8 ( 0.1 ns.

Inhibited Phenol Ionization in Reverse Micelles: Confinement Effect at the Nanometer Scale

“…On the contrary, the high ionic strength at the interface and the small amount of water make the proton-transfer process extremely slow in comparison with bulk water. [55] On the other hand, when W 0 is larger than 8-10 and the amount of water is enough to create the water pool with relatively free water molecules, [1,2,19] the processes can be described as those shown in Scheme 1. It should be noted that in this situation and because of the electrostatic repulsion between the phenolates species and the negative AOT RM interface, it is likely that the acid-base equilibrium takes place only at the water pool of the RMs.…”

Exploring anionic emission of 2-benzoyl benzimidazole in micellar environments

“…4a-c) [29]. The lifetime of 2BBI in an aqueous solvent is found to be tri-exponential with the values 60 ps (0.79), 600 ps (0.13) and 4000 ps (0.08) and on the addition of CTAB (15 mM) to this solution all the three lifetime components change.…”

Hydrogen‐Bonded Large Molecular Aggregates of Charged Amphiphiles and Unusual Rheology: Photochemistry and Photophysics of Hydroxyaromatic Dopants

“…More dramatic retardation has been observed in the case of solvation dynamics. While the solvation dynamics of water molecules occurs on the subpicosecond timescale in ordinary water, it is retarded by at least three orders of magnitude to the nanosecond timescale inside cyclodextrin cavities, micelles and microemulsions [97]. It has been demonstrated that in aqueous solution the rate of deprotonation of protonated aminopyrene increases nearly 3 times when the probes bind with cyclodextrin, while for 1-naphthol the deprotonation becomes almost 20 times slower.…”