Solvatochromism and temperature effects on the electronic absorption spectra of some azo dyes

The UV–visible electronic spectra of some azo dyes have been studied. The different bands observed in the electronic spectra of the compounds in various organic solvents have been assigned to the proper electronic transitions. The solvatochromic behaviour of these compounds was investigated by studying their visible spectra in several pure and mixed organic solvents. The longer wavelength band displayed by para-nitro azo dyes is assigned to an intermolecular charge-transfer transition. The solvated H-bonding complexes formed between N,N-dimethylformamide and the para-nitro azo dyes were investigated. ΔG and formation constant, the values of Kf of the molecular complexes formed in solution have been determined. The effects of increase of temperature and concentration dependent spectroscopic changes on the longer wavelength visible band of para-nitro azo dyes were also investigated.