Photoactive azoimine dyes: 4-(2-Pyridylazo)-N,N-diethylaniline and 4-(2-pyridylazo)-N,N-dimethylaniline: Computational and experimental investigation

4-(2-Pyridylazo)-N,N-dimethylaniline and 4-(2-pyridylazo)-N,N-diethylaniline, two photoactive azoimine dyes, were prepared from the reaction of 2-aminopyridine with N,N-dialkyl-1,4-nitrosoaniline at room temperature. Structural characterizations of these dyes using single crystal X-ray diffraction, 1H NMR, elemental analysis, mass spectroscopy and IR spectroscopy have been carried out. The X-ray structure indicates a trans configuration around the azo group. The photochemical behavior of these compounds differs from that of 2-phenylazopyridine, the non-dialkylamino substituent compound. The synthesized compounds show emission spectra at room temperature while 2-phenylazopyridine does not. The excitation spectra of these compounds differ from their absorption spectra which can be explained on the basis of the trans to cis photoisomerization which is supported by the TD-PBE0/6-31G(d,p) calculations. Both oxidation of the dialkylamino substituents (–NR2; R = –CH3 and –C2H5) and reduction of –NN–/–NN–− and –NN–−/–NN–2− were observed in the cyclic voltammogram indicating a π-acidity of both dyes.

Graphical abstractSynthesis, characterizations and computational studies of photoactive azoimine dyes: 4-(2-pyridylazo)-N,N-diethylaniline and 4-(2-pyridylazo)-N,N-dimethylaniline.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Photoactive azoimine dyes, 4-(2-pyridylazo)-N,N-diethylaniline and 4-(2-pyridylazo)-N,N-dimethylaniline, were synthesized and characterized. ► Both dyes are photo-active and emit fluorescence whereas the 2-phenylazopyridine does not. ► The observed excitation spectra of these dyes indicates the trans to cis photoisomerization which is confirmed by the TDDFT calculation.