The quadrupolar and octupolar cyano triphenylamines shows symmetry broken dipolar charge transfer state, however, its stability can be controlled by the rotation of N-C bond of amino and phenylene moiety.

A completely water-soluble, red emitting, multibranched sensor based on the electron-rich triphenylamine and electron-deficient rhodanine-3-acetic acid has been developed. The sensors mRA, dRA, and tRA, respectively, have one, two, and three rhodanine-3-acetic acid groups, responsible for the interaction with the metal ions as well as the solubility of the probe in water. mRA, dRA, and tRA senses Ag+ and Hg2+ ions in a buffer-free aqueous solution with the lowest detection level of 0.06 and 0.02 ppm, respectively. The yellow color of free sensor turns into purple and colorless in the presence of Ag+ and Hg2+ ions, respectively, which can be witnessed even by the naked eye. The metal ion preferentially binds with electron-deficient rhodanine-3-acetic acid owing to the presence of an ideal coordination environment. The distinctly different signals for Ag+ and Hg2+ ions occur because of the dissimilar binding modes, wherein the former extends and the latter breaks the π-electron conjugation that results in a different signaling mechanism. Nevertheless, the additional binding sites of dRA and tRA influences the binding constant and sensitivity; however, additional metal ion binding does not occur because of the changes in the electronic properties after initial binding. The applicability of these sensors in the biological medium was also tested using HaCaT cells using Ag+ and Hg2+ ions, which demonstrated the quenching of intense red fluorescence of the probe, and thus, these probes can be also be used as a potential biosensor.

No abstract

We are the first to report the synthesis of a new class of 2-cyanoarylacrylamide (2-CAA) derivatives and observe that the synthesized 2-CAA shows fluorescence properties due to the formation of a dimeric interaction of hydrogen bonds between carbonyl oxygens and amide hydrogens (C═O···H-N-C═O···H-N···); i.e., dimers are linked through dimeric N-H···O hydrogen bonds. The single-crystal X-ray structure shows molecules to be hydrogen-bonded dimers, which further form a parallel stacking arrangement, mediated by significant π-π interactions. The (1)H NMR and fluorescence spectral studies indicate the coexistence of amide and iminol tautomers in solution, which can be influenced by the nature of the solvent. Further, the excitation-wavelength-dependent fluorescence spectrum and the biexponential fluorescence decay profiles suggest the presence of more than one emitting species; i.e., amide and iminol tautomers coexists in solution. We have also shown that the equilibrium between the two tautomers can be tuned by the judicious choice of electron-donating or -withdrawing substituents.