Two salicylidene anilines derivatives, N-salicylidene-p-cyanoaniline (SA-CN) and N-salicylidene-p-carboxyaniline (SA-COOH), have been investigated in solid state with the purpose of getting a closer picture of their photophysical properties. The presented results are the first ones from a comprehensive investigation regarding the photodynamics of the proton transfer in the two compounds, influenced by different substitution patterns at the aniline ring. The molecular structures and the crystal packing with respect to substitution were revealed by single crystal X-Ray diffraction. Next, crystallography was used in conjunction with steady state diffuse reflectance and emission spectroscopy in crystalline state in order to explore the thermochromic and photochromic properties of the two SAs. The X-ray crystallographic analysis revealed the planar conformation for both compounds, which constitutes a necessary but not a sufficient ground for exhibiting thermochromic properties. The substitution groups at the aniline ring possess the electron – withdrawing (SA-CN) or proton donating/acceptor character (SA-COOH), so that the intermolecular interactions that control the supramolecular structure are different with this respect. Thus, the crystalline arrangement of SA-CN is governed by secondary interactions between the terminal cyano group, supplemented by two π - π interactions which promote a closed packing of molecules. As for SA-COOH, two strong intermolecular hydrogen bonds and one CH- π interaction are the basis for a more relaxed packing structure. In addition, the normal tautomeric form of both compounds at room temperature has been found to be the enol type, stabilized by a strong intramolecular hydrogen bond. The diffuse reflectance spectroscopy showed the presence of aggregates at room temperature, for both SA-CN and SA-COOH. The compounds also showed a moderate fluorescence in solid state at room temperature, which get stronger once the temperature was lowered (77 K), accompanied by a markedly change of color. The anomalous Stokes shift of the emission band with respect to the absorption of the enol form was explained by the radiative deactivation of the excited cis-keto species. These structures originate from a fast intramolecular proton/hydrogen atom transfer from the phenol-imine to a keto-amine form, at a time scale of nanoseconds (as observed from time resolved fluorescence measurements). The studies revealed the dissimilar behavior of SA-CN and SA-COOH under UV irradiation and on cooling down to nitrogen liquid temperature. The both compounds display thermochromism, as expected for the salicylidene anilines in crystalline state, but only one is also photochromic. The thermal relaxation was fast, with the restoration of the initial state in a few minutes, while the lifetime of the photochromic form was as long as several hours. Therefore, the relationship between the optical properties and the crystalline structure must be thoroughly comprehended, as most of the application ideas are focused on the use of photochromic and/or thermochromic Schiff bases in solid state.