Polymerization of fluorene-based monomers modified with thiavinylidene structure at 9-position and their optical properties

Two iodo-functionalized fluorene-based monomers having a thiavinylidene moiety at 9-position [2,7-diiodo-9-(n-hexylthiavinylidene)fluorene and 2,7-diiodo-9-((2-(2-methoxyethoxy)ethyl)thiavinylidene)fluorene] were synthesized. Suzuki coupling reactions with thienylboronic acids bearing a n-hexyl chain were subsequently conducted to obtain two thiophene-functionalized monomers [2,7-bis(4-hexylthienyl)-9-(n-hexylthiavinylidene)fluorene and 2,7-bis(3-hexylthienyl)-9-(n-hexylthiavinylidene)fluorene]. The dehalogenative polycondensation using Ni(cod)2/cod/bpy system and the oxidation coupling polymerization using FeCl3 gave three homopolymers (HP1, HP2, and HP3). The polymerization under Suzuki coupling condition gave three copolymers (CP1, CP2, and CP3). The number-averaged molecular weights ranged from 2500 to 23,000. The optical properties of polymer were dependent upon the character of arylene unit. Namely, HP1 solely consisting of a 9-(n-hexylthiavinylidene)fluorene segment demonstrated the short absorption maximum wavelength but the large red-shift (13 nm) from the solution state to film state. CP3 having a hydrophilic side chain showed the larger red-shift (13 nm) as compared with CP2 bearing the similar backbone and a hydrophobic side chain.