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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.

A new conducting polymer, poly(benzo [1,2-b:4,5-b']dithiophene-4,8-diyl vinylene) (1), has been prepared by pyrolysis of a precursor polymer 2, which, in turn, was prepared by a multistep synthetic sequence (Scheme 1). The polymer has a UV-vis spectral maximum at 501 nm (2.48 eV), band-gap (band edge) of 1.92 eV and with FeC1 3 doping a conductivity of 15 S cm-1. Quantum mechanical calculations using PRDDO, ab-initio and modified extended Hiickel methodology on the monomers, trimers and polymers, both aromatic and quinoid, provided structures and an absorption maximum band-gap which is consistent with either a planar aromatic polymer or a polymer which has both aromatic and quinoid units.

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