Enhanced thermo-stability and luminecent property of D-A copolymer based on fluorene and thieno[3,4-c]pyrrole-4,6-dione by incorporation of pentafluorobenzene group

A new monomer 1,3-dibromo-5-perfluorophenyl-thieno[3,4-c]pyrrole-4,6-dione was synthesized and the corresponded D-A copolymer poly{9,9-dioctylfluorene-2,7-diyl- alt -5-perfluorophenylthieno[3,4-c]pyrrole-4,6-dione} (PFFTPD) based on fluorene unit was synthesized. In order to investigate the effect of pentafluorobenzene substitution on the photo-physics and stability properties, the compared D-A copolymer poly{9,9-dioctylfluorene-2,7-diyl alt -5-octylthieno[3,4-c]pyrrole-4,6-dione} (PFCTPD) based on fluorene and octyl-thieno[3,4-c]pyrrole-4,6-dione was synthesized also. The obtained copolymer PFFTPD had a weight average molecular weight of 12178 with a narrow polydispersity index of 1.51, good solubility and higher thermal stability with T g of 131 ℃ and T d of 410 ℃. Compared to that of PFCTPD, the PL spectra of PFFTPD in solution and in thin film showed narrower half peak width and weaker shoulder peak in the long wavelength region. The luminescent efficiency and color purity were enhanced while lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels were decreased by incorporation of pentafluorobenzene group. Thus, the copolymer PFFTPD may be good candidate as emitting material applied in polymer light emitting diode (PLED).