Design and Synthesis of New Conjugated Porphyrin Copolymers for Optical-Electronic Applications
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Electronic Applications Biwang Jiang, Szu-Wei Yang, Phuong T. Lam, Wayne E. Jones Jr.* Department of Chemistry and Institute for Material Research, State University of New York at Binghamton, Binghamton, NY 13902. ABSTRACT New linear conjugated porphyrin polymers were synthesized by a palladium-catalyzed cross-coupling reaction of [5,15-bis(ethynyl)-10,20-bis (mesityl)porphyrin]zinc and diiodobenzene derivatives. Enhanced solubility of the conjugated porphyrin polymers was achieved by attachment of long alkyl ether or dialkyl amide groups to the aryl moiety, resulting in unambiguous characterization by 'H NMRLR, GPC, UV-Vis and fluorescence spectroscopies. The introduction of alkyl ether (electron donor) or dialkyl amide (electron acceptor) results in significant modulation of the electronic properties of the conjugated porphyrin polymers due to strong electronic coupling. The spectroscopic and electronic characterization of these materials provides for comparison to earlier preparations of ethynyl bridged conjugated copolymers in which electronic coupling was substantially weaker. INTRODUCTION The preparation of soluble, linear conjugated porphyrin polymers is attractive not only for their central importance for elucidation of fundamental biological processes such as photosynthesis, but also as a new class of conjugated materials with potential applications in optoelectronic devices [ 1-7]. Previous work on porphyrin dimers and oligomers constructed through the building block approach have developed substantial information on basic electronic coupling in conjugated systems. Building on the previous dimeric work, conjugated polymers with porphyrins incorporated directly into the conjugation would allow for additional modification in both the ground and excited state electronic structures of these new materials. One of the major problems for synthesizing porphyrin polymers is their insolubility [2, 8-9], which seriously limits characterization and applications. However, a few soluble, conjugated porphyrin polymers have been studied [1]. Recently, we synthesized a series of soluble meso-phenylporphyrin-based polymers, 1, with tunable electronic and photophysical properties. Unfortunately, the electronic communication
1 R=C, 2H25
Figure 1. Structure of meso-tetraphenylporphyrin-based polymer 323
Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
along the polymer backbone was limited due to steric interactions between the phenyl ortho proton and the porphyrin 13-hydrogen. The result of the steric interaction was a large dihedral angle between the porphyrin ring and the phenylenevinylene unit [6-7, 12] which limited electronic coupling through the yr-conjugation. Through modifications of the synthetic chemistry we have now prepared more fully conjugated porphyrin polymers in which ethynyl linking groups are inserted between the porphyrin and the conjugated polymer main chain. The spectroscopic and electrochemical characterization of these new polymers demonstrate enhanced electronic and optical
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