Structural defects in carbazolyl-containing polymers with polymethine dye impurities

Photoluminescence spectra and thermoluminescence curves of pure and doped c arbazolyl-containing polymers polyvinyl carbazole (PVC) and poly-hr-epoxypr opyl carbazole (PEPC) are investigated in the temperature range 5-300 K. Th e impurities are cationic indocarbocyanines with various lengths (n) of the polymethine chain: HIC (n = 1), HID (n = 2), HIT (n = 3) and squaryl dye H ISq with the same polymethine chain length and the same structure of hetero cyclic end groups as for the HID dye. It is found that solvation of dye mol ecules by polar groups of a polymer is accompanied by conformation changes in the polymer, which are considerably enhanced with increasing n, as well as upon a transition from a rigid-chain PVC macromolecule to a more flexibl e PEPC molecule. As a result, the concentration of structural defects, viz. , excimer-forming sites playing the role of traps for singlet excitons and charge carriers, increases considerably in doped PEPC films. This leads to the emergence of a band with a peak at 460 nm in the luminescence spectra o f PEPC films with HID and HIT and at 480 nm for films with the HISq impurit y, while the thermoluminescence curve for PEPC with HISq acquires an additi onal band with a peak at 275 K. (C) 2000 MAIK "Nauka/Interperiodica".