Solution‐Processable Carbazole‐Based Conjugated Dendritic Hosts for Power‐Efficient Blue‐Electrophosphorescent Devices

Abstract

A novel class of hosts suitable for solution processing has been developed based on a conjugated dendritic scaffold. By increasing the dendron generation, the highest occupied molecular orbital (HOMO) energy level can be tuned to facilitate hole injection, while the triplet energy remains at a high level, sufficient to host high-energy-triplet emitters. A power-efficient blue-electrophosphorescent device based on H2 is presented.

Blue Light Emitting Polyphenylene Dendrimers with Bipolar Charge Transport Moieties

“…The HOMOs of TPA and CAB were calculated to be −5.34 and −5.52 eV, respectively, corresponding to the HOMOs of the dendrimers. These values are very close to the HOMO of bare CAB (−5.61 eV) [37] and TPA (−5.35 eV) [59] (considering the measurement errors), suggesting little conjugation interactions between the PCs and the core in these dendrimers due to the high torsion angles between the PCs and the four phenyl groups bonding to pyrene, consistent with the crystal structure of compound 2 ( Figure S8). The HOMO of the core was deduced to be around −5.50 eV from the oxidation wave of PYPBD.…”

“…The observed dual emission in D2 and PYTPA under polar environments may give an insight into designing new emitters [58]. [24,59], from reported UPS measurements [23,37,60,61].…”

“…One with characteristic shape and significant intensity (ε: 230,000-250,000 L·mol −1 ·cm −1 ) is attributed to the energy transitions of PCs and polyphenylenes [37][38][39]. For example, in D1, the band with a maximum at 299 nm is characteristic of the CAB absorption [37], also consistent with the strongest absorption peak of PYCAB (a pyrene-cored polyphenylene dendrimer with CAB in the periphery, see Supplementary Materials) [24]. The band with a maximum at 319 nm can be assigned to the absorption of PBD [38], similar to that of PYPBD (a pyrene-cored polyphenylene dendrimer with PBDs in the periphery, see Scheme S1).…”

“…In addition, a TPA-and PBD-functionalized dendrimer D2 was prepared for comparison. The emission of CAB [37], PBD [38] and TPA [39] show good overlaps with the absorption of the core, i.e., 1,3,6,8-tetraphenylpyrene [40,41], for efficient surface-to-core energy transfers. For this purpose, shape-persistent polyphenylene dendrimers enable generation-by-generation (core-shell-surface) functionalization and OLEDs utilizing efficient surface-to-core energy transfers of pyrene-cored polyphenylene dendrimers have been reported [22][23][24].…”

“…In addition, a TPA-and PBD-functionalized dendrimer D2 was prepared for comparison. The emission of CAB [37], PBD [38] and TPA [39] show good overlaps with the absorption of the core, i.e., 1,3,6,8-tetraphenylpyrene [40,41], for efficient surface-to-core energy transfers. To summarize, in this contribution a new method to make polyphenylene dendrimers with donor-acceptor periphery is introduced.…”