Temperature activated ionic conductivity in gallium and indium phthalocyanines Sait Eren San a,⇑ , Mustafa Okutan a , Tebello Nyokong b , Mahmut Durmus ß c , Birol Ozturk d a Organic Electronics Group, Department of Physics, Gebze Institute of Technology, Gebze 41400, Kocaeli, Turkey b Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa c Department of Chemistry, Gebze Institute of Technology, Gebze 41400, Turkey d Department of Physics, Syracuse University, Syracuse, NY 13244, USA article info Article history: Received 18 November 2010 Accepted 31 December 2010 Available online 11 January 2011 Keywords: Dielectric spectroscopy Activation energy Phthalocyanines Semiconductors abstract The effects of introducing gallium and indium metals into phthalocyanine molecules were investigated via temperature and frequency dependent dielectric spectroscopy. The dielectric properties of Ga(III) and In(III) phthalocyanine pellets were measured at frequencies from 1 kHz to 1 MHz in the temperature range 300–530 K. The temperature dependence of the real part of the dielectric constant suggested that these compounds exhibit semiconductor behavior. The activation energy values were calculated from the Arrhenius plots at different frequencies. A distinct transition in these plots indicated the activation of ionic conductivity at higher temperatures. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Metallophthalocyanines (MPcs), a family of aromatic macrocy- cles based on an extensive delocalized 18-p electron system, are known not only as classical dyes in practical use but also as mod- ern functional materials in scientific research. There is a growing interest in the use of phthalocyanines (Pcs) in a variety of applica- tions, including non-linear optics [1], semiconductor devices [2], Langmuir–Blodgett films [3], electrochromic display devices [4], li- quid crystals [5] and as photosensitizers in photodynamic therapy (PDT) [6]. For non-linear optical applications, MPcs have advanta- ges over the currently used inorganic compounds due to their small dielectric constants [7], fast response times, ease of process- ability into optical components and their lower cost [1,7]. The structures of MPcs can be modulated in many ways, by changing the peripheral and non-peripheral substituents on the ring in addi- tion to changing the central metal and the axial ligands. Heavy metals, especially diamagnetic metals, play a major role in photosensitizing and optical limiting mechanisms because they enhance intersystem crossing through spin orbit coupling. This enhancement is desirable as it improves the probability of forming a large population in the triplet state. Axial ligands in MPcs play a key role in preventing or minimizing intermolecular interactions, which causes aggregation in solution. Aggregation can result in the fast decay of excited states. Indium and gallium are useful cen- tral metals in MPcs complexes since they are diamagnetic and are able to host axial ligands. Gallium and indium phthalocyanines have been reported to have good photosensitizing and optical lim- iting properties [1,7–11]. In the scope of this work, chlorogallium (ClGaPc) and chloroindi- um (ClInPc) phthalocyanine samples were examined with dielectric spectroscopy (DS). This method is shown to be a reliable tool for investigating molecular scale events and for the optimization of tai- lored materials [12–14]. The temperature dependence of the real part of their dielectric constants and dielectric loss were measured and analyzed. Activation energies of ClGaPc and ClInPc samples were also calculated at different frequencies. The conductivities and the activation energies of the samples increased at elevated temperatures, which were attributed to the activation of the ionic conductivity with increasing temperature. 2. Experimental 2.1. Sample preparation 2.1.1. ClGaPc This compound was synthesized and characterized according to the method reported elsewhere [15]. Briefly, a mixture of phthalo- nitrile (5 g, 0.04 mol), anhydrous gallium trichloride (5.5 g, 0.03 mol), and 20 mL of quinoline (double distilled over CaH 2 , deoxygenated) was refluxed for 1 h (particular attention was paid to the exclusion of water during this step). After cooling the mix- ture to approximately 273 K, the reaction mixture was filtered. The mixture was washed with toluene and methanol and dried at 383 K. The final solid compound had a purple color. Yield: 3.4 g (55%). Anal. Calc. for C 32 H 16 N 8 GaC1: C, 62.22; H, 2.61; N, 18.14. Found: C, 62.75; H, 2.34; N, 18.89%. 0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.12.047 ⇑ Corresponding author. Tel.: +90 262 605 13 13; fax: +90 262 653 84 97. E-mail address: erens@gyte.edu.tr (S.E. San). Polyhedron 30 (2011) 1023–1026 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly