bearing various substituents were designed and synthesized. These azo dyes were characterized by spectroscopic techniques such as 1H/13C NMR and HRMS or LCMS. Photophysical, NLO and protonation properties were investigated by experimentally and theoretically. The absorption maxima were observed in long wavelength in DMSO. The most stable tautomeric form of dyes which have tautomeric forms, were determined