SOLID-STATE ELECTRONIC ABSORPTION, FLUORESCENCE AND C-13 CPMAS NMR SPECTROSCOPIC STUDY OF THERMOCHROMIC AND PHOTOCHROMIC AROMATIC SCHIFF-BASES

Solid-state electronic absorption, fluorescence emission and C-13 CPMA S spectroscopies have been applied to a series of aromatic Schiff base s displaying both ground and excited state intramolecular proton trans fer phenomena. All the results can be explained on the basis of a ther mal equilibrium between enolimine and keto-enamine tautomeric forms in the crystalline state. Most of the studied compounds are thermochromi c. However, a few are photochromic. The carbon-13 NMR data in the soli d state show, in general, residual (C-13,N-14) dipolar coupling effect s. In certain cases, however, where fast proton transfer occurs in the ground state, these effects are shown to be self-decoupled.