J. Phys. France 44, 617-621 (1983)
DOI: 10.1051/jphys:01983004405061700

Temperature study of infrared reflection spectra on various faces of MTPP(TCNQ)2 single crystals

R. Swietlik et A. Graja

Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17/19, Poznan, Poland

Abstract
Crystals of the ion-radical salt MTPP(TCNQ)2 undergo a first-order structural phase transition at the temperature Tp = 315.7 K. This phase transition has a pronounced influence on the infrared spectra. In this paper we present and discuss the infrared spectra of MTPP(TCNQ)2 as a function of temperature. During thermal cycling we have observed an interesting thermal hysteresis of the reflection coefficients for different bands. Moreover, we have related the observed spectral modifications with the enthalpy of the phase transition.

Résumé
Les cristaux du sel d'ion-radical MTPP(TCNQ)2 subissent une transition de phase structurale du 1er ordre à la température de 315,7 K, se manifestant par des modifications importantes du spectre infrarouge qui seront présentées et discutées. Nous avons observé en outre une hystérèse des spectres de réflexion et avons montré qu'il existe une relation entre les changements du spectre et l'enthalpie de transition.

PACS
7830J - Organic compounds, polymers.
7868 - Optical properties of surfaces.

Key words
enthalpy -- infrared spectra of organic molecules and substances -- organic compounds -- solid state phase transformations