VARIABLE TEMPERATURE N-15 CPMAS NMR-STUDIES OF DYE TAUTOMERISM IN CRYSTALLINE AND AMORPHOUS ENVIRONMENTS

This paper deals with the question of how symmetric double minimum potentials of isolated bistable molecules are affected in the ordered or disordered solid state, in a timescale of slow molecular motion. It is shown that high resolution solid state NMR under conditions of magic angle spinning (MAS) and cross-polarization (CP) can contribute to answering this question. In particular, variable temperature high resolution solid state **1**5N CPMAS NMR spectra (CP equals cross polarization, MAS equals magic angle spinning) of **1**5N enriched tetraaza left bracket 14 right bracket annulene dyes in the crystalline state and imbedded in disordered glassy polystyrene are presented. These dyes interconvert fast between different tautomeric states whose gas phase degeneracy is lifted in the solid.