Solid-state /sup 15/N CPMAS NMR study of dye tautomerism in glassy polystyrene: site dependence of double minimum potentials and their motional averaging

Journal Article · Wed Oct 12 00:00:00 EDT 1988 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00229a013· OSTI ID:5837304

Wehrle, B; Zimmermann, H; Limbach, H H

The matrix effects on the high-resolution solid-state NMR line shapes of bistable molecules that are subject to rapid exchange between two isomers is described. Matrix effects are modeled in terms of a static superposition of different molecular environments or sites characterized by different equilibrium constants, i.e., differently perturbed double minimum potentials of the isomerism. A theory of inhomogeneously broadened NMR line shapes based on this model is presented. In addition, the effects of exchange between the different sites on the NMR line shapes are treated. Site exchange induces homogeneous line broadening and eventually liquid-type NMR spectra, where all molecules experience a similar motionally averaged effective double minimum potential of the isomerism within the NMR time scale. As an example, the variable-temperature /sup 15/N CPMAS NMR spectra of a /sup 15/N-enriched tetraaza(14)annulene dye (TTAA = 1,8-dihydro-5,7,12,14-tetramethyldibenzo(b,i)(/sup 15/N/sub 4/)-(1,4,8,11)-tetraazacyclotetradeca-4,6,11,13-tetraene, tetramethyldibenzotetraaza(14)annulene, C/sub 22/H/sub 24//sup 15/N/sub 4/), in the crystalline state and dissolved in glassy polystyrene, are presented. The /sup 15/N enrichment of TTAA is described, including the synthesis of its precursor o-phenylenediamine-/sup 15/N/sub 2/. Solid-solution NMR studies provide information about details of molecular rearrangements in a time scale of slow solvent reorientation. In addition, dyes such as tetraaza(14)annulenes can be useful for probing microscopic order and motion in glasses by NMR. 52 references, 8 figures.

• Research Organization: Universitaet Freiburg i. Br. Alberstrasse (Germany, F.R.)
• OSTI ID: 5837304
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 110:21
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DYES
ISOMERIZATION
EXPERIMENTAL DATA
MATRIX MATERIALS
NITROGEN 15
NMR SPECTRA
CHEMICAL REACTIONS
DATA
INFORMATION
ISOTOPES
LIGHT NUCLEI
MATERIALS
NITROGEN ISOTOPES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
SPECTRA
STABLE ISOTOPES
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation