THIOPHENE-BASED PI-CONJUGATED EMITTING POLYMERS - SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF OLY[2-(DODECYLOXY)-5-METHYL-M-PHENYLENEETHYNYLENE] AND -5-METHYL-M-BIS(ETHYNYL)PHENYLENEOLIGOTHIENYLENE]S

A series of copolymers, oly[2-(dodecyloxy)-5-methyl-m-phenyleneethynyl ene] and 5-methyl-m-bis(ethynyl)phenyleneoligothienylene]s, in which e thynylene units are inserted into both of the meta positions of every phenylene for the elimination of the steric hindrance around the meta linkages, was synthesized by a Heck type coupling reaction. The result ing polymers were characterized by infrared and nuclear magnetic reson ance spectroscopy and by elemental analysis and gel permeation chromat ography. Their optical spectra show that the absorption and emission m axima regularly shift to lower energy with increasing number of the th iophene units between the consecutive m-phenylene linkages. It is conf irmed that the role of the m-phenylene as an interrupting block does n ot come from the steric hindrance around the Linkage but from the intr insic property, e.g., the MO of the m-phenylene moiety. The quantum yi elds of their emissions gradually decrease with a decrease in concentr ation of the ethynylated m-phenylene units on the polymer backbone and the Stockes shifts increase. Both of the trends indicate that a nonra diative decay of the excited states increases with an increase in the possible configurations of thiophene rings within the repeating active block.