Synthesis and optoelectronic properties of random copolymers derived from fluorene and 2,5-bis(2,1,3-benzothiadiazolyl) silole

A novel series of soluble conjugated random copolymers (PFO- BTS) derived from 9,9-dioctylfluorene (FO) and bis(2,1,3-benzothiadiazolyl)silole ( BTS) were synthesized by Suzuki coupling reactions. The feed ratios of FO to BTS were 99: 1, 95: 5, 90: 10, and 85:15. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence ( PL), and electroluminescence (EL). The elemental analyses of the copolymers indicated that FO and BTS contents in the copolymers were very close to that of the feed compositions. Compared with the solution PL, complete PL excitation energy transfer from the PFO segments to the BTS units could be achieved by film PL at lower BTS content. The films of the copolymers exhibited PL quantum yields between 22 and 34%. EL devices with a configuration of ITO/PEDOT/PFO-BTS/Ba/Al demonstrated that the BTS units could serve as powerful exciton traps, giving orange-red EL emissions. The PFO-BTS15 was utilized to fabricate blend-type PLEDs with the PFO, the EL efficiency was improved to 1.37% with a weight ratio of PFO-BTS15 : PFO = 1 : 4.