Synthesis and optical properties of poly(thienylacetylenes)

3-Ethynyl-4-(trimethylsilyl)thiophene (1a) and 3-ethynyl-4-bromothiophene ( 1b) selectively undergo acetylene polymerizations in the presence of the Mo Cl5- and WCl6-Ph3SiH catalysts to give soluble, high-molecular-weight poly( thienylacetylenes) (2) (M-w up to 602000) in high yields (up to 100%). Ligh t transmission spectra of THF solutions of 2 continuously red-shift with in creasing concentration. The concentratochromism shows a logarithmic concent ration dependence; that is, the optical transitions of 2 are predictably tu nable by simply changing their concentrations.