DFT Study of Structure of Azo-Linked 4H-Pyran Dyes

Pyran derivatives have attracted many chemists due to their various biological activities and pharmacological properties such as antiviral, antibacterial and anti-inflammatory activities. In recent years, various studies have been devoted to the synthesis of novel derivatives of these compounds and several protocols have been devised for their preparation. In this research, Density Functional Theory (DFT) calculations at the B3LYP level are used to optimize the geometry of azo-linked 4H-pyran dyes. In the continuation of our study, we were interested in evaluation of homoaromaticity of the selected compounds using Nucleus Independent Chemical Shift (NICS). The studies released that, the presence of various azo substitute in atom 2 or 3 of pyran ring, make little change in NICS values and the numbers of groups or the reach of groups to atom 4 of pyran ring, and decrease the NICS value. Also, the NICS values caused by compounds containing aryl azo bridge are more suitable than other bridges. The data related HOMO-LUMO gap, also, relatively, emphasized the data caused by NICS.