Synthesis and electronic structure of 1,2-heteroarylethynes: Potential monomers for low bandgap conductive polymers

A series of 1,2-heteroarylethynes which are potential monomers to low bandgap materials were synthesized and their He I photoelectron spectra measured and assigned with the aid of empirical arguments and semi-empirical MO calculations. The electronic structure analysis reveals that C ≡ C bond is an efficient 'relay' of π-electrons and that it supports inter-ring conjugation. The efficiency depends on the nature of ring heteroatom, but not on its position within the ring. The importance of C ≡ C bond relay is discussed in the broader context of conjugated polymer applications.