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

Abstract

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 →π^* 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.

Get full access to this article

View all access options for this article.

References

[1] Lim K C and Heeger A J 1985 J. Chem. Phys. 82 530-530

[2] Tokura Y , Kanetake T , Ishikawa K and Koda T 1987 Synthetic Metals 18 412-412

[3] Kanetake T , Tokura Y , Koda T , Kotaka T and Ohnuma H 1985 J. Phys. Soc. Japan 54 4026-4026

[4] Exarhos G J , Risen W M and Baughman R H 1976 J. Am. Chem. Soc. 98 482-482

[5] Shand M L , Chance R R , Le Postollec M and Schott M 1981 Phys. Rev. B 25 4431-4431

[6] Yoshino K , Nakajima S , Park D H and Sugimoto R I 1988 Japan. J. Appl. Phys. 27 L456-L456

[7] Yoshino K , Nakajima S , Gu H B and Sugimoto R I 1987 Japan. J. Appl. Phys. 26 L2048-L2048

[8] Valdimir D and Richard M S 1987 Phys. Rev. B 15 2781-2781

[9] Ziman J M 1979 Models of Disorder (Cambridge: Cambridge University Press)

10.

[10] Osman M A , Othman A A and Abd-Alla M A 1991 J. Phys. D: Appl. Phys. 24 1206-1206

11.

[11] Tauc J 1972 The Optical Properties of Solids ed F Abeles (Amsterdam: North-Holland) p 277-277

12.

[12] Arai T and Martin T P 1977 J. Non-Cryst. Solids 23 186-186

13.

[13] Schweizer K S 1986 J. Chem. Phys. 85 4181-4181

14.

[14] Chance R R , Patel G N and Witt J D 1979 J. Chem. Phys. 17 206-206

15.

[15] Tauc J 1970 Res. Bull. 5 721-721

16.

[16] Davis E A and Mott N F 1970 Phil. Mag. 22 903-903

17.

[17] Tauc J 1966 Phys. Status Solidi 15 627-627

18.

[18] Watanbe I and Okumura T 1986 Japan. J. Appl. Phys. 25 1851-1851

19.

[19] Urbach F 1953 Phys. Rev. 92 1324-1324

20.

[20] Mott N F and Davis E A 1971 Electronic Processes in Non-crystalline Materials 2nd edn (Oxford: Clarendon) p 289-289

21.

[21] Dow J D 1975 Optical Properties of Highly Transparent Solids (New York: Plenum) p 131–143

22.

[22] Pal U , Saha S , Chudhuri A K , Rao V V and Banerjee H D 1989 J. Phys. D: Appl. Phys. 22 970-970

23.

[23] Frenkel S Ya and Elyashevich G K 1971 Vysokomol. Soedin A 13 493-493

24.

[24] Abd-Alla M A and El-Shahawy A S 1991 J. Appl. Polym. Sci. 42 461-461

25.

[25] Perepechko I I 1981 An Introduction to Polymer Physics (Moscow: Mir) p 266-266

26.

[26] Ferry J D 1980 Viscoelastic Properties of Polymers 3rd edn (New York: Wiley)

27.

[27] Elliott S R 1990 Physics of Amorphous Materials 2nd edn (New York: Wiley)

28.

[28] Abd-Alla M A , Aly K I and Hammam A S 1989 High Perform. Polym. 1 323-323