Influence of peripheral substituents on the optical properties of heterocyclic azo dyes

•Bathochromic shift of the absorption edge in heterocyclic azo dyes was observed.•The value of refractive index depends on the type of substitution pattern in azo dyes.•The heterocyclic azo dyes are transparent up to about 2.0 eV.

Optical properties, such as the real and imaginary parts of the dielectric function and the optical energy band gap, of new heterocyclic azo dyes thin films were investigated using spectroscopic ellipsometry combined with transmittance measurements. The topography of studied compounds was also examined by atomic force microscopy.It was found that the optical properties of the azo dyes materials strongly depend on the type of substitution in the azobenzene moiety, namely leads to a change in the value of refractive index, as well as bathochromic shifts of the absorption structure.