Synthesis of some new solvatochromic 1(4)-substituted Pyrazol-5-one Azo derivatives

New 1-(2ʹ-benzthyazolyl)-3-methyl-pyrazol-5-one-4-substituted azo derivatives have been prepared and characterised by elemental analysis, IR, 1H-NMR and UV-VIS. The solvatochromic behaviour was investigated and their ionisation constants were determined. These dyes generally absorb near-infrared light at around 11,000 cm-1 and this is the most favourable wavelength region for semiconductor laser optical recording dye medium.