Environmental Engineering and Management Journal February 2015, Vol.14, No. 2, 421-431 http://omicron.ch.tuiasi.ro/EEMJ/ “Gheorghe Asachi” Technical University of Iasi, Romania SYNTHESIS AND ELECTRON TRANSPORT PROPERTIES OF SOME NEW 4,7-PHENANTHROLINE DERIVATIVES IN THIN FILMS Cristina M. Al Matarneh 1 , Ramona Danac 1 , Liviu Leontie 2 , Florin Tudorache 3 , Iulian Petrila 3 , Felicia Iacomi 2 , Aurelian Carlescu 2 , Gigel Nedelcu 2 , Ionel Mangalagiu 1 1 Alexandru Ioan Cuza University of Iasi, Faculty of Chemistry, 11 Carol I Blvd., 700506 Iasi, Romania 2 Alexandru Ioan Cuza University of Iasi, Faculty of Physics, 11 Carol I Blvd., 700506 Iasi, Romania 3 Alexandru Ioan Cuza University of Iasi, Interdisciplinary Research Department - RAMTECH, 11 Carol I Blvd., 700506 Iasi, Romania Abstract Temperature-dependent d.c. electric conductivity of some recently synthesized organic compounds, 4,7-phenanthroline derivatives is studied. Thin-film samples (d=0.34-0.63 m) spin-coated from dimethylformamide solutions onto glass substrates have been used. Organic films with reproducible electron transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range of 298523K. Examined organic compounds in thin films are polycrystalline and display typical n-type semiconductor behavior. The activation energy of d. c. electric conduction ranges between 0.09 and 0.46 eV and is influenced by nature of substituents, degree of conjugation systems and packing capacity of compounds. In the higher temperature range (T>433 K), the electron transport in examined compounds can be interpreted in terms of the band gap representation model, while in the lower temperature range, the Mott’s variable-range hopping conduction model was found to be appropriate. Some of the investigated compounds hold promise for thermistor applications. Key words: chemical synthesis, electric conductivity, organic compounds, thin films Received: November, 2014; Revised final: February, 2015; Accepted: February, 2015  Author to whom all correspondence should be addressed: email: lleontie@uaic.ro 1. Introduction Organic semiconductor compounds (in form of monomers, polymers, plastics, synthetic rubbers, etc.) represent an emerging class of materials, extensively explored over the past four decades. The ample worldwide research effort addressed divers aspects, from material synthesis and growth (single crystals, thin films, nanostructures), study of electron transport, optical, and photophysical/photochemical properties, to a wide range of technological applications (Iniewski, 2011; Logothetidis, 2012). The extended -electron systems of organic semiconductors can be easily tuned through ‘molecular engineering’ (molecular structure modification by chemical substitution). In this way, divers classes of emerging materials, ranging from superconducting and semiconducting, to conducting ones have been synthesized to date (Fraxedas, 2006; Lebed, 2008). Due to their remarkable characteristics, significant electroluminescence, high mobilities of charge carriers, energy band gap in the IR–vis domain, relevant photophysical characteristics, combined with high processability and versatility, easy shaping and manufacture, compatibility with mechanically flexible substrates and facile integration with divers physical/chemical/biological functionalities (Bernards et al., 2008; Huang et al., 2014; Turbiez et al., 2005), organic semiconductors