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.