SYNTHESIS AND OPTICAL PROPERTIES OF POLY (THIENYLACETYLENES)*

3 -Ethynyl-4-(trimethylsilyl)thiophene (1a) and 3 -ethynyl-4-bromothiophene (1 b ) selectivelyundergo acetylene polymerizations in the presence of the MoCl_5- and WCl_6-Ph_3SiH catalysts to give soluble,high-molecular-weight poly(thienylacetylenes) (2) (M_w up to 602000) in high yields (up to 100%). Lighttransmission spectra of THF solutions of 2 continuously red-shift with increasing concentration. Theconcentratochromism shows a logarithmic concentration dependence; that is, the optical transitions of 2 arepredictably tunable by simply changing their concentrations.