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Temperature Dependence of Absorption Spectra and Optical Parameters for Polyester Films of Dibenzylidene Cyclohexanone

A A Othman

Physics Department, Faculty of Science, Assiut University, Assiut, Egypt

M A Abd-Alla

Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

Effect of temperature on the optical absorption spectra and optical parameters is investigated in new synthesized polyester films of poly[oxyiso-phthaloyloxy(2-methoxy-p-phenylene)methylidyne(2-oxo-1, 3-cyclohexanediylidyne)methylidyne(3-methoxy-p-phenylene)] (I) and poly[oxysebacoyloxy-(2-methoxy-p-phenylene) methylidene (2-oxo-1, 3-cyclohexanedi-ylidene)-methy-lidene-(3-methoxy-p-phenylene)] (II). Absorption measurements are carried out in the temperature range 80–370 K and in the photon energy range 1.9–4 eV. The optical absorption spectra of polymers I and II reveal excitonic absorption bands at 80 and 120 K respectively. These bands are associated with n ^* optical transitions along polymer backbone chains. Analysis of optical absorption data indicates that the Tauc equation for indirect optical transitions successfully explains the optical absorption process in polymeric film I, whereas Urbach’s law is more suitable for describing the optical absorption in polymeric film II. Temperature dependence of the optical bandgap, E^opt_g, the Tauc slope B, and the width of Urbach’s tail states (E_e) exhibits anomalous parabolic behaviour which can be explained in terms of various current theories. Moreover, DSC, x-ray diffraction and morphological studies by TEM are used in the explanation of the experimental results. The values of optical parameters, as well as the temperature coefficient of the optical bandgap for these polymers, are calculated and reported.

High Performance Polymers, Vol. 9, No. 4, 397-411 (1997)
DOI: 10.1088/0954-0083/9/4/004


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