Photophysical and Electrochemical Properties of Novel Luminescent and Photoconductive Copolymers

Photophysical and electrochemical properties of novel luminescent carbazole-based, carbazole-fluorene and fluorene-bithiophene copolymers, and photoconductive copolymers containing 4,6- bis(3-dodecylthien-2-yl)thieno[3,4-c][1,2,5]thiadiazole as electron acceptor unit and various electron donor unit (9,9-dioctylfluorene, 9,9-bis(2-ethylhexyl)fluorene, 2,5-bis(dodecyloxy)benzene, 2,5- didodecylbenzene, 3,3′-didodecyl-2,2′-bithiophene, 2,7-carbazole or dithieno[3,2-b:2′,3′-d]silole derivatives) were studied. Effects of molecular weight and side-chain nature and length on photophysical properties are reported. Luminescent carbazolebased and carbazole-fluorene copolymers exhibited an intense photoluminescent (PL) emission in blue spectral region with maxima at about 417-419 nm in tetrahydrofuran (THF) solutions and at 430-436 nm in thin films, whereas 9,9-dihexadecylfluorenebithiophene copolymers PL emission in green spectral region with maxima at about 495 nm in THF solutions and at 542 nm in thin films. The donor-acceptor copolymers absorb in a long-wavelength region up to near infrared and possess a narrow optical band gap in the range of 1.1 - 1.4 eV depending on the character of donor units and alkyl side-chain nature. They exhibited ambipolar redox properties, high electron affinity, electrochromic and thermochromic behavior.