New conjugated polymers with donor-acceptor architectures: Synthesis and photophysics of carbazole-quinoline and phenothiazine-quinoline copolymers and oligomers exhibiting large intramolecular charge transfer

Alternating carbazole-quinoline and phenothiazine-quinoline donor-acceptor conjugated copolymers and a corresponding oligomer were synthesized, and their solution and solid-state photophysics were investigated. The new copolymers, poly(2,2'-9-methyl-3,6-carbazolylene-6,6'-bis(4-phenylquinoline)) and poly(2,2'-10-methyl-3,7-phenothiazylene-6,6'-bis(4-phenylquinoline)), had intrinsic viscosities of 11.2-22.0 dL/g, indicating very high molecular weights. The optical band gaps of the new copolymers were 2.35-2.64 eV, which are significantly smaller than the corresponding homopolymers. The absorption and emission spectra of the related donor-acceptor oligomers, 3,6-[bis(4-phenyl-2-quinolyl)]-9-methylcarbazole and 3,7-[bis(4-phenyl-2-quinolyl)]-10-methylphenothiazine, in solvents of varying polarity showed positive solvatochromism. An unusual dual fluorescence, with a blue emission band at 454 nm and an orange emission band at 584 nm, was observed in solid films of the carbazole-linked oligomer and related to intramolecular excitons and intermolecular excimers. Solid-state emission from the phenothiazine oligomer and copolymer was from intramolecular excitons with strong charge-transfer character. The red solid-state emission from the carbazole copolymer originated from intermolecular excimers with dominant fluorescence lifetimes of 2-10 ns. The observed intramolecular charge-transfer effects on photophysics and properties were larger in the phenothiazine-containing oligomer and copolymer than the corresponding carbazole-containing materials, reflecting the fact that phenothiazine is a stronger electron-donating unit. Preliminary results suggest that the oligomers and copolymers are useful for light-emitting and photovoltaic devices.