Structural defects in carbazolyl-containing polymers with polymethine dye impurities

Abstract

Photoluminescence spectra and thermoluminescence curves of pure and doped carbazolyl-containing polymers polyvinyl carbazole (PVC) and poly-N-epoxypropyl carbazole (PEPC) are investigated in the temperature range 5–300 K. The impurities are cationic indocarbocyanines with various lengths (n) of the polymethine chain: HIC (n=1), HID (n=2), HIT (n=3) and squaryl dye HISq with the same polymethine chain length and the same structure of heterocyclic end groups as for the HID dye. It is found that solvation of dye molecules 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 flexible 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 of PEPC films with HID and HIT and at 480 nm for films with the HISq impurity, while the thermoluminescence curve for PEPC with HISq acquires an additional band with a peak at 275 K.