Isatin pentafluorophenylhydrazones: interesting conformational change during anion sensing

Abstract

Easily synthesized and highly efficient F− and CH3COO− anion sensors based on reversible keto (hydrazo)/enolate (azo) acid–base equilibrium followed by interesting conformational change in solution.

Tautomeric photoswitches: anion-assisted azo/azine-to-hydrazone photochromism

“…Although this behaviour indicates photoswitching between hydrazone A and azo B forms, unchanged UV-Vis spectrum of C form at 590 nm irradiation could still result from fast back thermal reaction of anionic hydrazone form D. Such extremely fast back thermal reaction (isomerization) in a microsecond to a second timescale is commonly known in push-pull azobenzenes and was recently found also in push-pull azopyrimidines. 39 However, absence of a fast signal decay in ultrafast UV-Vis kinetics measurement aer 590 nm excitation (Fig. S30 †) together with an absence of ground state depletion signal at 590 nm in transient absorption spectrum of C ( Fig.…”

“…† 39 As indicated, the additon of F À to initial Z hydrazone form (A) can stabilize blue azo form through hydrogen bonding (B) or can lead to deprotonation (azo anion C formation) with very similar UV-Vis spectrum (Scheme 4). 39 Moreover, because of practically identical electron density (and thus shielding of protons) in B and C, also 1 H NMR spectra of both forms B and C are almost identical. However, F À anion excess (>2 equiv.)…”

Effect of a =X-NH-Fragment, (X = C, N), on Z/E Isomerization and ON/OFF Functionality of Isatin Arylhydrazones, ((Arylamino)Methylene)Indolin-2-Ones and Their Anions

“…the phenyl-bonded nitro group ( 3 E and 3 Z ) by its -I inductive effect and the resonance +R electron effect stabilizes the E azo form and shifts the tautomeric equilibrium towards the E azo form. The -I effect of the substituents on the aryl itself has little effect on tautomeric equilibrium [ 13 ].…”

Isatin as a simple, highly selective and sensitive colorimetric sensor for fluoride anion

“…Isatin 1 is also considered important in many physiological pathways [48][49][50]. Apart from its applications in medicinal chemistry [47], it has been extensively employed as a signaling unit in various receptors [51,52] and some of its derivatives have also been investigated as chemosensors for anion detection [53,54]. Careful analysis of its features reveals that isatin 1 has an acidic NH group and intense color which are prime requirements for a chemosensor [29,[42][43][44][45][46].…”