A solid-state (CP-MAS)13C nuclear magnetic resonance study of selected photo(thermo)chromic spiro-(indolinonaphthoxazine)s

Liquid and solid-state¹³C NMR data are reported for three photo(thermo)chromic spiro-(indolinonaphthoxazine)s,1–3. The isotropic¹³C chemical shifts are almost identical in the solid state and in solution. Therefore, the structures in the solid state are fully retained in solution. Quantitative analysis of the spinning side-band pattern of¹³C CP-MAS NMR spectra gave shielding anisotropies and asymmetry parameters different for1–3 and related to the substitution pattern. For3 the tensor componentσ ₃₃, assumed to be perpendicular to the aromatic ring, is more shielded than the corresponding components of1 and2 probably because of the near orthogonality between the substituent piperidinyl ring and the naphthoxazinic system. A correlation between shielding anisotropy and thermochromic activity is suggested.