Heterocyclic Polymers and Copolymers with Controlled Optoelectronic Properties
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HETEROCYCLIC POLYMERS AND COPOLYMERS WITH CONTROLLED OPTOELECTRONIC PROPERTIES JOSE P. RUIZ, KASINATH NAYAK, ANDREW D. CHILD, DENNIS S. MARYNICK* AND JOHN R. REYNOLDS* Center for Advanced Polymer Research, Department of Chemistry, The University of Texas at Arlington, Arlington, Texas 76019-0065 ABSTRACT A series of aromatic polymers and copolymers have been investigated that contain a combination of 2,5-thienylene and 1,4-phenylene linkages. 1,4-Bis-(2-thienyl)phenylene monomers have been prepared with a variety of substituents on the 2,5-phenylene positions. Subsequent oxidative polymerization of these monomers, both chemically and electrochemically, yield a family of polymers containing a thiophene-phenylene-thiophene repeat unit. Theoretical modeling, using both PRDDO and ab initio methods, has been used to correlate the thiophene-phenylene torsional angles with band gaps. In addition, polymer band structure has been investigated using the Extended Hiickel method.
INTRODUCTION During the past decade, a significant amount of effort has been directed towards the architectural modification of electrically conductive polymers. This work has been stimulated by a variety of emerging potential applications [1]. Much of the research has been aimed at improving both the physical and electronic properties of these polymers. Notable among these are solution and melt processability, environmental stability, mechanical integrity and controllable conductive and optical properties. One conjugated polymer of interest arises when both phenylene and thiophene moieties are incorporated into the polymer backbone. Synthetic efforts which have been pursued include the incorporation of sulfur into a polymer consisting of phenylene and diketone [2] or acetylene [3) units to form a completely alternating thiophene/phenylene backbone; the random incorporation of phenylene and thiophene repeat units [4] utilizing a Grignard reaction; and the utilization of monomeric bis-thienylphenylene which can be electrochemically polymerized to form polymers with bithiophene/phenylene repeat units [5-7]. In this work, we present the synthesis of a series of 1,4-bis(2-thienyl)-2,5disubstitutedphenylenes and their polymerization using both chemical and electrochemical oxidative polymerizations. The electrochemical, spectroscopic and electrical properties of these polymers are correlated with theoretical calculations demonstrating the utility of theory in helping to direct experimentation.
RESULTS AND DISCUSSION Monomer Preparation The monomers, 1,4-bis(2-thienyl)benzene, la, and 1,4-bis(2-thienyl)-2,5-dimethyl benzene, lb, were prepared from the corresponding 1,4-diiodobenzene derivative [8] and 2thienyl magnesium bromide with a nickel catalyst. The reaction of 2-thienyl copper with 1,4diiodo-2,5-dimethoxybenzene in refluxing pyridine [9,10] yielded a crystalline product 1,4bis(2-thienyl)-2,5-dimethoxybenzene, 1c, after recrystallization in methanol. Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society
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Electron Density Theoret
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