Unexpected Structural Defects In A Main-Chain Conjugated Polymer Synthesized Through Suzuki-Miyaura Cross Coupling Polymerization

Suzuki-Miyaura cross coupling (SMC) copolymerization of 3,8-dibromo-1,10-phenanthroline (PhenBr(2)) and 9,9-dioctylfluorene-2,7-diboronic acid (DOF[B(OH)(2)](2) was conducted aiming to synthesized an alternating copolymer composed of 1,10-phenanthroline-3,8-diyl and 9,9-dioctylfluorene-2,7-diyl units in a mixture of 1,2-dimethoxyethane and water using Pd(PPh3)(4) and K2CO3 as catalysts at different temperatures. Side reactions were unexpectedly found to take place in the reactions at 100 degrees C where hydroxy and carbonyl groups appeared to be introduced probably to 1,10-phenanthroline units. Such reactions were more remarkable in the polymerization than in a model reaction leading to a triad molecule consisting of central 1,10-phenanthroline-3,8-diyl unit connected to two 9,9-dioctylfluorene-2-yl units, suggesting that a longer growing species has a role in such reactions. The extent of side reactions was higher with H2O than with D2O and was negligible with (H2O)-O-18. The polymer with structural defects showed photo absorbance and emission profiles and thermal properties which were remarkably different from those of the alternating copolymer without structural defects.