Dielectric and Conductivity Studies on Cobalt Phthalocyanine Tetramers S. Saravanan 1 , C. Joseph Mathai 1 , M. R. Anantharaman 1 , S. Venkatachalam 2 , P. V. Prabhakaran 2 1 Department of Physics, Cochin University of Science and Technology, Cochin 682 022 India 2 PCM, Vikram Sarabhai Space Centre, Trivandrum 695 022, India Received 24 January 2003; accepted 23 July 2003 ABSTRACT: Electrically conductive organic and metal- loorganic polymers are of great interest and they have ap- plications in electronic, optical, photonic, photoelectric, elec- trochemical, and dielectric devices. Tetrameric cobalt phtha- locyanine was prepared by conventional chemical method. The dielectric permittivity of the tetrameric cobalt phthalo- cyanine sample was evaluated from the observed capaci- tance values in the frequency range 100 KHz to 5 MHz and in the temperature range of 300 to 383°K. It is found that the system obeys the Maxwell Wagner relaxation of space charge phenomenon. Further, from the permittivity studies AC conductivity was evaluated. The values of AC conduc- tivity and DC conductivity were compared. Activation en- ergy was calculated. To understand the conduction mecha- nism Mott’s variable range hopping model was applied to the system. The T -1/4 behavior of the DC conductivity along with the values of Mott’s Temperature (T 0 ), density of states at the Fermi energy N (E F ), and range of hopping R and hopping energy W indicate that the transport of charge carriers are by three-dimensional variable range hopping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2529 –2535, 2004 Key words: dielectric properties; conjugated polymers; tet- ramers; AC and DC conductivities; conduction mechanism INTRODUCTION Phthalocyanines and their polymers are well known for their unique photoconducting and semiconducting properties. 1–7 Though the discovery of these materials is accidental, the phthalocyanine ring is a good ligand and every element in the periodic table, including nonmetallic elements such as silicon and phospho- rous, form a complex with phthalocyanine ring. 1,5,8 Materials based on phthalocyanines have been of par- ticular significance in many fields concerning energy conversion (photovoltaic and solar cells), electropho- tography, photosensitizers, gas sensors, rectifying de- vices, electrochromism, optical data storage, LB films, liquid crystals, and nonlinear optics. 9,10 The electrical properties of polymeric phthalocyanine are of interest because of their conjugated structure and stability against light, heat, moisture, and air. Hence polymeric phthalocyanines are suitable candidates for use as en- vironmentally stable electrically conductive materi- als. 11–14 Polymeric metallophthalocyanines of copper (Cu), nickel (Ni), and cobalt (Co) possess large ex- tended conjugated structures and exhibit high con- ductivity. 12,15,16 Among them, tetrameric cobalt phtha- locyanine exhibits greater conductivity than the nickel and copper phthalocyanine tetramers. 12 Hopping or tunneling conduction mechanism is the usual trans- port of charge carriers found in conducting polymers. To understand the semiconducting and dielectric properties of tetrameric cobalt phthalocyanine com- pound, a systematic investigation on these properties and their variation with temperature and frequency is attempted in this paper. The mechanism of electrical conduction is explained using Mott’s variable range hopping model. EXPERIMENT Preparation of cobalt phthalocyanine tetramer Tetramer of cobalt phthalocyanine was prepared, pu- rified, and characterized by the methods reported ear- lier. 17,18 In this method, cobalt sulfate, pyromellitic dianhydride, excess urea, ammonium chloride, and ammonium molybdate were ground well and heated at 180°C in nitrobenzene media for 12 h. The reaction mixture was then cooled and washed with methanol several times to remove nitrobenzene. The crude product was further boiled with 2N sodium hydroxide containing sodium chloride and filtered. The residue was acidified with hydrochloric acid and washed sev- eral times and dried to obtain phthalocyanine tet- ramer. The structure of tetrameric cobalt phthalocya- nine is shown in Figure 1. Elemental analysis Elemental analysis was carried out in a Perkin–Elmer 2400 elemental analyser, which uses a combustion Correspondence to M. R. Anantharaman (mra@cusat.ac.in). Journal of Applied Polymer Science, Vol. 91, 2529 –2535 (2004) © 2003 Wiley Periodicals, Inc.