Fluorescence of isatin N‐phenylsemicarbazones: aggregation and hydrazide–hydrazonol tautomerism

Abstract

The solution behavior of isatin N‐phenylsemicarbazones and their interaction with anions was investigated using fluorescence technique. Existence of associate/hydrazide (keto)/hydrazonol (enol) tautomeric equilibrium explains the solvent, concentration and excitation/emission effect on fluorescence of studied compounds. Both static and dynamic fluorescence measurements, together with quenching experiments, confirm the dynamic equilibrium between individual tautomeric forms with different emissive character in solution. Because of the nonfluorescent character of hydrazonol tautomer, the quantitative description of tautomeric equilibrium and dimerization was performed using UV–Vis spectroscopy. Determined apparent association constants Kass for interaction with F− anion using Stern–Volmer plots correlate well with the previously determined sensor sensitivity. Their high values indicate again the most acidic urea NH group deprotonation and not the hydrogen bonded sensor : hydrazonol 1:1 complex formation. Copyright © 2015 John Wiley & Sons, Ltd.

The Scavenging of DPPH, Galvinoxyl and ABTS Radicals by Imine Analogs of Resveratrol

“…To test this assumption we performed the following experiment. According to the work of Cigáň et al [32], creation of self-aggregates can be determined from concentration-dependence of absorption or fluorescence spectra. The formation of self-aggregates should be manifested by a shift of emission maxima or by a shape change in absorption/fluorescence spectra with an increase of concentration of the studied compound.…”

Exploring the possibilities of double proton transfer in hydrazides: A theoretical approach

“…It is quite interesting to know that hydrazides exhibit keto‐enol tautomerism upon photoexcitation . Tautomerism in hydrazides is characterized by translocation of a proton from a donor (N―H) moiety to an acceptor moiety (C═O) with a pre‐established intramolecular hydrogen bond giving birth to a phototautomer phenomenon, commonly termed as excited state intramolecular proton transfer (ESIPT).…”

“…It is quite interesting to know that hydrazides exhibit keto-enol tautomerism upon photoexcitation. [1][2][3] Tautomerism in hydrazides is characterized by translocation of a proton from a donor (N-H) moiety to an acceptor moiety (C═O) with a pre-established intramolecular hydrogen bond giving birth to a phototautomer phenomenon, commonly termed as excited state intramolecular proton transfer (ESIPT). Proton transfer is primly induced by the energy difference pertaining to locally excited state and the relaxed excited state, and the gradient spread over a potential energy surface (PES) connecting these two extremities governs the relative kinetics of the system.…”