Considerable interest has been made in the development of materials that are optically responsive and have the potential to be useful in photonic technology. Organic materials based on the azobenzene moiety have received significant attention because of their photoresponsive properties that results from the trans-cis-trans isomerization of azo chromophores. Reversible transformation between more stable thermodynamically trans-azobenzene and less stable cisazobenzene can be monitored by UV or visible light irradiation or thermally in the dark. The photoisomerization process can be followed by monitoring the intensity of the absorption band of the trans-isomers at around 350 nm while the cis-isomers show a less intense absorption band at longer wavelengths. In this way the light response becomes of special importance in order to control at will the molecule configuration. Reversible trans-cis-trans isomerization of the molecules causes structural changes resulting also in spectral changes. During trans- to -cis conversion, the intensity of the absorption band corresponding to the n – pi* transition increases, while the pi – pi* band decreases [1]. Structural changes of the azobenzene are reflected in obtaining a stable dipole moment by the cis-isomer (3.0 D) and in the change in geometry caused by a reduction in the distance between carbon atoms in positions 4 and 4’ from 9.0 Å for the trans-isomer to 5.5 Å for the cis-isomer [2,3]. The derivatives used in this study are new aromatic diamines containing azo group, namely 3-o–tolylazo-pyridine-2,6-diamine and 3-p–tolylazo-pyridine-2,6-diamine. These diamines have been synthesized via the one-step diazonium coupling reaction of ortho- or para-toluidine diazonium chloride with 2,6-diaminopyridine, as shown in the Scheme. The obtained diamines were characterized by elemental analysis, FTIR, 1H NMR and UV-Vis spectroscopy. The isomerization behaviour was monitored following the changes in ultraviolet-visible absorption spectra.