Synthesis and spectral investigation of novel 4-aryl-5-(aryldiazenyl)thiazole dyes festooned with fluorene moiety: Experimental and theoretical insight

A series of novel 4-aryl-5-(aryldiazenyl)thiazole dyes 7a-h pendant to fluorene group were synthesized form easily accessible starting materials. The absorption spectra of the synthesized azodyes were recorded in different solvents with variable chemical and physical properties. Structural Elucidation of the synthesized azodyes were carried out by UV-vis, IR and NMR spectroscopies as well as elemental analyses. Different solvent parameters, such as microscopic solvent polarity, Kamlet-Taft and Catalan parameters were employed in order to assess the solute-solvent interactions and the solvatochromic shifts of the absorption maximum of the 4-aryl-5-(aryldia-zenyl)thiazole dyes under investigation. The solvent scales constitute the most appropriate method for inter -preting the solvatochromic behavior of the synthesized azodyes. Furthermore, the dyes' absorption ability revealed that the substituent effect on UV-vis absorption spectra is strongly influenced by the electronic nature of the substituent on the 1-phenyl ring. It was also observed that the absorption spectra were sensitive to acidic and basic media. The synthesized azo compounds showed spectral changes that revealed that azo tautomers formed at acidic pH while hydrazo tautomers at alkaline pH. To gain a thorough understanding of the stability and geometrical characteristics of the azo-hydrazo tautomers, DFT calculations were also performed on the synthetic dyes.