A SOLID-STATE (CP-MAS) C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY OF SELECTED PHOTO(THERMO)CHROMIC SPIRO-(INDOLINONAPHTHOXAZINE)S

Liquid and solid-state C-13 NMR data are reported for three photo(ther mo)chromic spiro(indolinonaphthoxazine)s, 1-3. The isotropic C-13 chem ical shifts are almost identical in the solid state and in solution. T herefore, the structures in the solid state are fully retained in solu tion. Quantitative analysis of the spinning side-band pattern of C-13 CP-MAS NMR spectra gave shielding anisotropies and asymmetry parameter s different for 1-3 and related to the substitution pattern. For 3 the tensor component sigma33, assumed to be perpendicular to the aromatic ring, is more shielded than the corresponding components of 1 and 2 p robably because of the near orthogonality between the substituent pipe ridinyl ring and the naphthoxazinic system. A correlation between shie lding anisotropy and thermochromic activity is suggested.