Synthesis, Spectroscopic, Physicochemical, Crystal Structure and DFT Studies of 4,5,6,7-tetrahydro-1-benzothiophene-3-carbonitrile Based Azomethine Dyes

Three new azomethine dyes were synthesized via a simple condensation method using 2-amino-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carbonitrile and a variety of aldehydes. The structures of synthesized compounds were established by spectroscopic (FT-IR, 1H NMR, 13C NMR, MS) and elemental analyses. UV-Vis and fluorescence spectroscopy measurements proved that all compounds have good absorbance and fluorescence properties. Fluorescence polarity studies demonstrated that these compounds were sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including singlet absorption, extinction coefficient, Stokes shift, oscillator strength and dipole moment, were investigated in order to explore the analytical potential of the synthesized compounds. Three-dimensional structures were studied using single crystal x-ray diffraction. Optimized geometries, electronic structure and frontier molecular orbital energies were studied theoretically, and the energy gap (ΔE) of II was found to be relatively greater than those for I and III, while I and III have almost the same energy gaps.