Modulation of Excited-State Intramolecular Proton Transfer Reaction of 1-Hydroxy-2-naphthaldehyde in Different Supramolecular Assemblies

Abstract

The excited-state intramolecular proton transfer (ESIPT) reaction of 1-hydroxy-2-naphthaldehyde (HN12) has been studied within the interior of the supramolecular assemblies of alpha-, beta-, and gamma-cyclodextrins (CD) and biomimicking environments of ionic (SDS) and non-ionic (TW-20) micelles. Fluorescence measurements are used to investigate the effect of various supramolecular assemblies on the ESIPT reaction by monitoring the large Stokes-shifted tautomer emission of HN12. Enhanced tautomer emission in the microencapsulated state predicts favorable ESIPT reaction in the supramoleuclar assemblies. Benesi-Hildebrand plots have been employed to ascertain that the stoichiometric ratios of the complexes formed between HN12 and CDs are 1:2, 1:1, and 1:1 for alpha-, beta-, and gamma-CD, respectively. The binding constants (K(1)) and free-energy change (DeltaG) for inclusion complexation are also determined from the linearized Benesi-Hildebrand plots. Steady-state fluorescence anisotropy, REES, excitation anisotropy, and fluorescence lifetime measurements are in line with other experimental findings. Differential action of urea on SDS and TW-20-bound probe has also been investigated.

Constrained photophysics of an ESIPT probe within β-cyclodextrin nanocavity and chaotrope-induced perturbation of the binding phenomenon: Implication towards hydrophobic interaction mechanism between urea and the molecular probe

“…Fluorescence quantum yield (U) has been determined using bnaphthol as the secondary standard (U = 0.23 in methylcyclohexane) [5,6,27,28] using the following equation:…”

“…The excellence of the fits was judged by v 2 criteria and visual inspection of the residuals of the fitted function to the data. Mean (average) fluorescence lifetimes were calculated using the following equation [5,27,28]:…”

“…By virtue of their unique structural architecture, (a hydrophobic cavity and a relatively hydrophilic periphery due to the hydroxyl groups of the receptor edges) CDs are able to form inclusion complexes with a wide variety of substances [1][2][3][4][5][6][7], of course subject to the compatibility of sizes between the 'host' and 'guest' molecules [8]. There has been burgeoning interest in studying the spectroscopic and photophysical properties of fluorescent molecules in different organized media for a better understanding of the nature and site of interaction in true biological systems.…”

“…Quite a number of works have been reported on the study of intramolecular charge transfer (ICT) [7,[11][12][13][14][15][16] and intermolecular excited-state proton transfer (ESPT) [17,18] reactions in inclusion complexes of CDs, micelles, reverse micelles and so forth. But a little pursuance is noted in the literature on the implementation of ESIPT probes [5,19]. In the present work we intend to follow the study of inclusion complexes of CDs utilizing a probe endowed with ESIPT molecular framework 3,5,6-trichlorosalicylic acid (TCSA, Scheme 1).…”

Fabrication of cyclodextrins-procainamide supramolecular self-assembly: Shape-shifting of nanosheet into microtubular structure

“…Decay of the fluorescence of the drug has been studied in water and 0.01 M CD at the emission maxima (355 nm) of the drug (Lakowicz, 1986;Paul, Samanta, & Guchhait, 2010). The excitation wavelength of PCA was 295 nm.…”