th  - 1987 - 51st ENC Conference

WF26
TEMPERATUREVARIABLE SOLID SOLUTION CPMAS NMR STUDIES
OF DYES IN GLASSY POLYMERS
Bernd Wehrle and Plans-Heinrich Limbach*
Institut ffir Physikalische Chemie der Universitit Freiburg l.Br.,
Albertstr.21, 7800 Freiburg, West Germany
Photoreactive solids such as dyes imbedded in solid tnatrices are of
considerable technical and theoretical interest. We report here the use of
temperature variable CPMAS NMR spectroscopy for the study of structure
and dynamics of dyes dissolved in glassy polymers. As in liquid solution
state NMR, solution state NMR studies are greatly aided if matrix signals
are absent in the spectra. Since most of the known organic dyes but few
polymers contain nitrogen we propose here I~N CPMAS NMR of I~N en-
riched dyes. This method has also the advantage that spectra can be re-
corded even at fairly low dye concentrations. Thus, interesting lnfor-
mations about the structure and the dynamics of dyes in solid matrices
can be obtained, such as fast chemical reactions inside the dye, rotational
and transverse diffusion, or slow crystallization.
In particular, we present here low temperature I~,N CPMAS NMR spectra
of a tetraazaannulene derivative (TTAA) dissolved to a few percent in
glassy polystyrene, PMMA, etc. In crystalline TTAA fasl proton tau~o-
merism leads to sharp I~N NMR lines whith temperature dependent positi-
ons. ~ By contrast, the solid solution ~N NMR lines of TTAA in glassy po-
lymers are broad but show a characteristic temperature dependence. 2D
experiments reveal that this broadening is inhomogeneous. The lineshapes
can be simulated with the assumption of a broad gaussian distribution of
different sites in the glass in which dye molecules experience a differenl
reaction profile of tautomerism. Within the NMR timescale the molecu]es do
not rotate nor are able to exchange sites at room temperature. Thus, dye
tautomerism can be used as a novel probe for local order. Some conse-
quences of for the understandung of chemical reactions in condensed
matter are discussed.
1. H.H.Limbach, B.Wehrle, H.Zimmermann, R.D.Kendrick, C.S.Yannoni
j.Am.Chem.Soc., in press).