Fused Heterocyclic Aromatics as Potential Organic Semiconductors: a Theoretical Study
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Fused Heterocyclic Aromatics as Potential Organic Semiconductors: a Theoretical Study Faleh Al Tal1, Phuong-T T. Pham2, Mariam Ali Al-Maadeed3, and Mamoun M. Bader4 1 Department of Electrical Engineering, Qatar University, Doha, Qatar 2 Department of Chemistry, Pennsylvania State University Worthington Scranton, Dunmore, PA, 18512 3 Department of Mathematics and Physics, Qatar University, Doha, Qatar 4 Department of Chemistry, Pennsylvania State University, 76 Univeristy Drive, Hazleton, PA, 18202 ABSTRACT We report herein the results of density functional theory calculations of the geometric and electronic structure for a series of fused heterocyclic compounds. These molecules were compared with the corresponding carbocyclic oligoacenes, which are currently being experimentally investigated for use as organic semiconductors. The impact of various structural modifications on this class of compounds on the calculated structures is examined. The results of our calculations reveal that such materials hold exceptional promise as organic semiconductors.
INTRODUCTION The interest in conjugated organic molecules continues to grow due to their unique optical and electrical properties with potential for applications in devices such as field-effect transistors (FETs), light-emitting diodes (LEDs), and solar cells.[1] In particular, oligothiophenes, and polyacenes such as pentacene, have been investigated more than any other classes of compounds.[2-4] The closely related heterocyclic counterparts, such as ladder-type oligomers have not received much attention. The formation of planar backbone structures and the improvement in thermal stability and conjugation are especially important features of these materials. Sulfur-containing derivatives, such as phenothiazine ladder polymers and oligomers are particularly interesting. Synthesis of these materials has been reported in the literature and is rather straightforward. For example, phenothiazine systems are readily obtained by reaction of dichloro-p-benzoquinones and aminothiophenols.[5] In this paper we report our findings from a computational study aimed at addressing some questions in the molecular design of organic semiconductors based on these materials. Ideally we set out to carry out a systematic investigation which would yield the data needed to answer the following questions. How would carbocyclic compounds compare with their heterocyclic counterparts? What is the effect of chain length? What is the role of heteroatom? What effect does the type and relative position of hetero atoms have? What is the effect of the molecular shape and symmetry?
COMPUTATIONAL METHOD All calculations were performed using Density Functional methods at the B3LYP levels as implemented in the software package Spartan 06 using desktop PC[6]. The calculations were carried out on isolated gas molecules and as such are not meant to provide absolute values of the band gap. RESULTS AND DISCUSSION Linear Oligoacenes We first consider the series of fused linear carbocyclic aromatic com
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