Tuning the Electronic Properties of 2‑Cyano-3-phenylacrylamide Derivatives

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 1H 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.