Synthesis and color tuning of new fluorene-based copolymers

A series of copolymers, poly{9,9-bis(2'-ethylhexyl)fluorene-2,7-diyl-co-2,5-bis(2-thienyl-1-cyanovinyl)-1-(2'-ethylhexyloxy)-4-methoxybenzene-5",5"'-diyl} (PFTCVB), were synthesized from the monomers 2,7-dibromo-9,9-bis(2'-ethylhexyl)fluorene and 2,5-bis(2-(5'-bromothienyl)-1-cyanovinyl)-1-(2"-ethylhexyloxy)-4-methoxybenzene (BTCVB) through the Ni(0)-mediated polymerization. The copolymers were characterized using FT-IR spectroscopy, UV-vis spectroscopy, TGA, photoluminescence (PL) and electroluminescence (EL) spectroscopy, elemental analysis, and molecular weight studies. The synthesized copolymers showed an absorption maximum at about 380 nm, and between 425 and 600 nm the absorption increased with increasing fraction of thiophene-containing monomer 4 (BTCVB). In PL, the emission maxima of the copolymers were red-shifted as the fraction of BTCVB increases, despite the copolymers showing little variation in UV-vis absorption characteristics. Light-emitting devices were fabricated in an ITO (indium-tin oxide)/PEDOT/polymer/LiF/Al configuration. The EL spectra showed similar emissions to the PL results, and the copolymer containing 15 mol % of BTCVB showed bright-red emission.