Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 951529, 7 pages http://dx.doi.org/10.1155/2013/951529 Research Article Synthesis and Electrical and Gas Sensing Properties of Some 5-(Quinolinylmethylene)-2-thioxodihydropyrimidine- 4,6(1H,5H)-dione and 5-(Quinolinylmethylene)pyrimidine-2, 4,6(1H,3H,5H)-trione Derivatives H. Kerim Beker, 1 Mevlude Canlica, 1 Alper Akinci, 2 Ahmet Altindal, 3 and Seniz Kaban 2 1 Department of Chemistry, Faculty of Science and Art, Davutpasa Campus, Yildiz Technical University, Esenler, 34220 Istanbul, Turkey 2 Institute of Science and Technology, Yildiz Central Campus, Yildiz Technical University, Barbaros Bulvari, Besiktas, 34349 Istanbul, Turkey 3 Department of Physics, Faculty of Science and Art, Davutpasa Campus, Yildiz Technical University, Esenler, 34220 Istanbul, Turkey Correspondence should be addressed to H. Kerim Beker; kerimbeker@hotmail.com and M. Canlica; mcanlica@yahoo.com Received 5 June 2012; Accepted 29 August 2012 Academic Editor: Hakan Arslan Copyright © 2013 H. Kerim Beker et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Eight new 5-(quinolinylmethylene)barbituric acid derivatives were synthesized by the reaction of 1,3-dimethylbarbituric acid and 1,3-diethyl-2-thiobarbituric acid with quinoline-4-carboxaldehydes and several quinoline-2-carboxaldehydes via Knoevenagel condensation. e novel compounds were characterized by 1 H NMR, 13 C NMR, mass, IR, and UV-visible spectral data and elemental analyses. d.c. and a.c. conduction properties of the compounds were investigated in the frequency range of 40–10 5 Hz and temperature range 295–440 K. e d.c. results showed an activated conductivity dependence on temperature for all �lms. Obtained data reveal that a.c. conductivity obeys the relation ac () = A  and exponent  is found to decrease by increasing temperature. e analysis of the a.c. conduction data showed that the CBH model is the dominant conduction mechanism for the electron transport in the �lms. �as sensing properties of the �lms for the volatile organic compounds (VOCs) were also investigated in the same temperature range. Maximum sensitivity to VOCs was observed at around 360 K for compound . 1. Introduction Heterocyclic compounds and their derivatives, which are developing quite rapidly and becoming more important day by day, constitute a very important branch of organic chemistry. ese compounds containing nitrogen, sulfur, and oxygen as ring members are commonly used in various �elds of industry as analytical reagents, ligands, dyestuffs, pharmaceuticals, and bioindicators. In addition to these, barbituric and thiobarbituric acid derivatives are well known as antibacterials [1], sedatives [2], herbicides [3], fungicides [4], and antiviral agents with their speci�c properties [5]. On the other hand, barbiturates having heterocyclic moieties have attracted considerable attention due to their potential pharmacological activity, and have become valuable alterna- tives in drug design [6, 7]. e electrical characterizations (d.c. and a.c.) of the materials are crucial in order to study relevant mechanisms of conduction and to realize its future applications. For example, to produce any device whose active layer is made of this kind of material, we need to know the effect of the temperature on both a.c. and d.c. electrical properties of the �lm, so as to carry out the accurate design. Measurements of d.c. and a.c. conductivity is also a reliable method to study the localised states near the band edges below the conduction and above the valance bands produced by the substitutional disorders which control many of the optoelectronic properties. Hence, a study of d.c. and a.c. conductivity in these materials will throw light on the nature of these levels. ere is an increasing demand for the detection of volatile organic solvents in the �eld of environmental analysis, industrial process control, and work-place monitoring. A number of materials, for