Synthesis and characterization of blue light emitters based on dimers of fluorene: Effects of different pendant electron-withdrawing moieties

2,4,6-Triphenyl-1,3,5-triazine, diphenylmethanone and triphenylphosphine oxide were introduced into the 9-position of one fluorene moiety to produce donor-acceptor vertically structured emitters DFTRZ, DFCO and DFPO. The Tg of DFTRZ, DFCO and DFPO solid powder are 135 °C, 89 °C and 97 °C, and DFTRZ with the most rigid receptor of 2,4,6-triphenyl-1,3,5-triazine showed the highest thermal stability, whose Td reached 436 °C, far exceeding those of DFCO and DFPO. The absolute photoluminescence quantum yields of DFTRZ, DFCO and DFPO solid powders are 14.35%, 1.13% and 7.57%, and the molecular framework of DFTRZ is meaningful to enhance the absolute photoluminescence quantum yields of obtained emitters. The donor-acceptor vertical structures do not endow these emitters with expected thermally activated delayed fluorescence emission. Beside the local emission of fluorene-based dimers, DFTRZ exhibits additional intramolecular charge transfer emission in polar solvents. The unique polar-induced dual emission of DFTRZ in solvents deteriorates the emission purity of the obtained emitter, and this embarrassment can be eased by DFPO in some degree. However, the dual light emission of DFTRZ in some polar solvents is useful to be senser and produce white light emission in solution. The maximum luminance of devices with bis (2-methyldibenzo[f, h] quinoxaline) (acetylacetonate) iridium (III) doped in emitters DFTRZ, DFCO and DFPO is higher than those of 2,3,5,6-tetrakis[3,6-bis(1,1-dimethylethyl)− 9 H-carbazol-9-yl]benzonitrile doped devices, and the corresponding maximum luminance is 16050 cd·m−2 for DFTRZ, 4545 cd·m−2 for DFPO and 11025 cd·m−2 for DFCO. DFPO is the best host of blue light emitters for OLED applications in term of color purity. [Display omitted]