The excited-state intramolecular proton transfer (ESIPT) reaction of l-hydroxy-2-naphthaldehyde (HN12) has been studied within the interior of the supramolecular assemblies of α-, β-, and γ-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 α-, β-, and γ-CD, respectively. The binding constants (K1) and free-energy change (ΔG) 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. © 2009 American Chemical Society.