Blue light-emitting polymers containing ortho-linking carbazole-based benzothiophene-S, S-dioxide derivative

Abstract

The blue light-emitting polymers PF-CzBTOs and PCz-CzBTOs were synthesized by Suzuki polycondensation via introducing ortho-linking N-(2-decyltetradecyl) carbazole bis- [2,3-b,6,7-b]benzo[d]thiophene-S,S-dioxide (CzBTO) into the polyfluorene (PF) and polycarbazole (PCz) backbone, respectively. All the resulted copolymers showed high thermal stability with the glass transition temperatures (Tg) of over 130 °C. The fluorescence quantum yields (ФPL) are in the range of 41%–59% and 20%–31% for PF-CzBTOs and PCz-CzBTOs, respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers are basically unchanged with the increase of CzBTO content in the copolymers. The PL spectra of copolymers showed only a faint broadening with the increase of CzBTO content in the copolymers, and with the increase of the solvent polarities, indicating no remarkable ICT effect in polymers containing ortho-linking CzBTO moiety. The copolymers showed a pure blue emission with a CIE coordinates of (0.15, 0.11) for the PF-CzBTO10, and a CIE coordinates of (0.17, 0.18) for PCz-CzBTO15. The results indicated that the strategy of introducing ortho-linking CzBTO unit into the polyfluorene or polycarbazole backbone can effectively restrain ICT effect and result in the pure blue emission.