Poly(benzo[1,2-b:4,5-b']dithiophene-4,8-diylvinylene). Synthesis, Properties, and Electronic Structure of a New Dithiophene-Fused p-Phenylenevinylene Conducting Polymer

Abstract

A new conducting polymer poly(benzo[1,2-b:4,5-~']dithiophene-4,8-diylvinylene) (11, has been synthesized by the pyrolysis of the soluble precursor polymer 2, which was itself prepared by a multistep synthesis. The polymer is burgundy, and a film has A , , = 503 nm (2.47 eV) and a band-gap (band edge) of 1.89 eV. Upon doping (FeC13) the polymer film becomes light blue-green and has a conductivity of 60 S cm-*. The original absorption peak at 503 nm decreases, while two new near-IR absorptions at 860 and 1860 nm appear during doping, which is reversible. Quantum mechanical calculations show a rather low rotational barrier in the monomer, and additional calculations on various oligomers and the polymer suggest that the stable form of the polymer is aromatic and planar. IntroductionAs part of our long-standing program to study new highly conjugated, electrically conducting polymer^,^-^ we are currently attempting to design, prepare, and characterize materials which might show enhanced conductivity. This may be achieved in several ways, including synthesizing materials which are more ordered on a molecular level, stretch-orienting polymer chains, and increasing the dimensionality of the polymer array. To this end we are designing and preparing systems which, in addition to the one-dimensionality of the polymer backbone, also have controlled degrees of increased dimensionality transverse to the chain axis direction. This should increase interchain electronic interactions and provide the needed two-dimensional conduction network. Our approach combines the known attributes of charge-transfer complexes which contribute to their electrical conductivity, and even superconductivity, where conduction occurs along stacks of these ring systems, with the chain conduction of doped, high molecular weight conjugated polymers. These attributes include their flat, broad conjugated nature, their ability to form ordered structures, and the fact that they contain a number of large, polarizable atoms such as sulfur which allow for orbital interaction, through short intermolecular S-S distances, from one planar molecule to a nearest n e i g h b~r .~ Some of these chargetransfer salts are shown in Figure 1.l0The initial system we have chosen is poly(benzo[l,2-b:4,5-b']dithiophene-4,8-diylvinylene) (1) since this appears to possess many of the desired characteristics. Since we required a material that could be cast into films, we have synthesized this polymer via a processable precursor polymer. We now report on the preparation, properties, and quantum mechanical calculations of this novel material.

Synthesis and Thin-Film Transistor Performance of Poly(4,8-didodecylbenzo[1,2-b:4,5-b‘]dithiophene)

“…Benzodithiophenes have been used as vacuum-evaporated small-molecule semiconductors in OTFTs. − The parent structure has a near-planar molecular plane which would be conducive to establishing a close molecular π−π stacking order for efficient charge carrier transport to afford high FET mobility. , However, these are small molecular semiconductors which generally form brittle thin films and may not be suitable for use in fabricating flexible integrated circuits. On the other hand, we believe that polymers based on the benzodithiophene building blocks, which have rarely been investigated, , might serve as interesting semiconductors for flexible OTFT circuits on plastic substrates. We selected poly(4,8-didodecylbenzo[1,2-b:4,5-b‘]dithiophene) as our target polymer semiconductor for its solution processability from the presence of a relatively long alkyl chain and self-assembly capability from the regioregular placement of alkyl chains along the polymer backbone.…”

Photoaddition Reactions of Acetylene and Butadiyne Derivatives to Benzodithiophene,1

“…In the classic review about thiophene, Wynberg wrote, “To many chemists thiophene is merely one member of the inexhaustible supply of heterocyclic compounds.” Despite being known for 100+ years, it has never found large-scale industrial use save in some semisynthetic pencillins . Today, due mostly to their efficient electrochemical polymerization, thiophene-containing building blocks play major roles in the development of new materials ranging from conducting polymers, organic semiconductors, and polymeric liquid crystals . The fascinating photochemistry of thiophenes, some of which was also first reported by Wynberg, remains largely unexplored.…”