ABSTRACT
The hyperfluorescence (HF) system has drawn great attention in display technology. However, the energy loss mechanism by low reverse intersystem crossing rate (kRISC) and the Dexter energy transfer (DET) channel is still challenging. Here, we demonstrate that this can be mitigated by the quadrupolar donor-acceptor-donor (D-A-D) type of thermally activated delayed fluorescence (TADF) sensitizer materials, DBA-DmICz and DBA-DTMCz. Further, the HF device with DBA-DTMCz and ν-DABNA exhibited 43.9% of high maximum external quantum efficiency (EQEmax) with the Commission Internationale de l'Éclairage coordinates of (0.12, 0.16). The efficiency values recorded for the device are among the highest reported for HF devices. Such high efficiency is assisted by hindered DET process through i) high kRISC, and ii) shielded lowest unoccupied molecular orbital with the presence of two donors in D-A-D type of skeleton. Our current study provides an effective way of designing TADF sensitizer for future HF technology.
ABSTRACT
The novel carbazole-based multiresonance types of thermally activated delayed fluorescence (MR-TADF) emitters of mICz-DABNA and BFCz-DABNA are reported, and their spectroscopic properties are investigated with the inductive effect on the central nitrogen atom for pure and deep blue emission. With the introduction of electron-donating/-withdrawing properties of substituents, emitters exhibited the bathochromic/hypsochromic shifted emission, respectively, compared to simple carbazole-based MR-TADF. Moreover, their spectral bandwidths became narrower. Theoretical calculation indicated that the meta-positioned bulky moiety restricts the molecular geometry discrepancy and reduces the Huang-Rhys factors. Particularly, the organic light-emitting diode (OLED) with 3% BFCz-DABNA exhibited the maximum external quantum efficiency of 28.0% with the Commission International de l'Éclairage (CIE) of (0.13, 0.09), which is the best record value among single-boron MR-TADF devices of CIE y < 0.10.
ABSTRACT
Seventy nine derivatives of thieno[2,3-b]quinolines, tetrahydrothieno[2,3-b]quinoline, dihydrocyclopenta[b]thieno[3,2-e]pyridine, cyclohepta[b]thieno[3,2-e]pyridine and hexahydrocycloocta[b]thieno[3,2-e]pyridine were either synthesized or obtained commercially and tested for their antiproliferative activity against HCT116, MDA-MB-468 and MDA-MB-231 human cancer cell lines. The most potent eight compounds were active against all cell lines with IC50 values in the 80-250nM range. In general hexahydrocycloocta[b]thieno[3,2-e]pyridines were most active with increasing activity observed as larger cycloalkyl rings were fused to the pyridine ring.
