SYNTHESIS AND ELECTRONIC STRUCTURE OF HETEROCYCLIC COMPOUNDS

Abstract

A series of 1,2-heteroarylethynes, which are potential monomers for low bandgap polymer materials, was successfully synthesized in good yields by the reaction of thienylethynylstannane with arylbromides in the presence of Pd catalyst. Their He I photoelectron spectra were measured and assigned with the aid of empirical arguments and semi-empirical MO calculations. The electronic structure analysis revealed that the C ? C bond is an efficient "relay" of ?-electrons and that it supports inter-ring conjugation. The conjugation efficiency depends on the nature of ring heteroatom, but not on its position within the ring. The importance of C ? C bond relay was discussed in the broader context of conjugated polymer applications. Relationship between deduced electronic structure and formation of novel-polymer materials was also discussed. The results suggested that 2,2-bisthienylethyne is a better candidate than other isomers for the new electrically conducting polymers. A novel synthetic approach to tellurophene and its derivatives 2,5-bis(3- hydroxy-3-methyl-1-butynyl)tellurophene and 2-(3-hydroxy-3-methyl-1-butynyl)tellurophene was developed. The reaction of butadiyne or its functional derivatives with sodium telluride (generated from tellurium powder and NaBH4 instead of liquid ammonia) took place under mild conditions to give the target compounds in good yields. Two different solvent systems in this reaction were investigated and it was found that an optimum yield of tellurophene was obtained when using a 5:3 mixture of ethanol-methanol or a 3:2 mixture of water-ethanol. On the other hand, 2,5-bis(3-hydroxy-3-methyl-1-butynyl)tellurophene and 2-(3-hydroxy3-methyl-1-butynyl)tellurophene could be selectively generated by controlling the quantity of sodium hydroxide. 2,2'-Bitellurophenc was synthesized. Its electronic structure was discussed on the basis of He I and He II photoelectron spectra and the comparison of electronic structure along 2,2'-bichalcophene series.