Efficient pure blue hyperfluorescence devices utilizing quadrupolar donor-acceptor-donor type of thermally activated delayed fluorescence sensitizers

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.

Neoteric Advances in Oxygen Bridged Triaryl Boron‐based Delayed Fluorescent Materials for Organic Light Emitting Diodes

“…The 20 wt % doped films showed excellent PLQY for OBO-I of 81 % and OBO-II of 98 % compared to (DBA-DTMCz). [52] The design is based on substituting high triplet energy donors (mICz and TMCz) on DOBNA acceptor at para-to the Batom. Both materials revealed high PLQY and promising TADF characteristics.…”

“…Among the reported boron based acceptors, the fully fused oxygen bridged triarylboron, 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DOBNA) attracted significant attention because of its unique properties such as multi-resonance feature, rigid molecular structure, narrowband emission, and excellent TADF characteristics (Figure 3). [52][53][54][55][56][86][87][88][89] Consequently, numerous DOB-NA-based TADF emitters have been developed by adopting different molecular designs and achieved very high EQE. However, these materials often displayed severe efficiency rolloff and poor operational stability, which needs to be addressed from the molecular design perspective.…”

Realignment of Local and Charge-Transfer Excited States in Promoting Room-Temperature Phosphorescence of Organic Aggregates

“…Organic RTP materials with unique photophysical properties due to the radiative transition of triplet excitons are highly attractive for optoelectronics, molecular imaging, information encryption, anticounterfeiting, and many others. ,,– Significant progress has been made in designing and extending the performance and scope of RTP materials . Accumulating research work demonstrates that D–A, D–π–A, and D–A–D′ molecular structures are commonly employed to design RTP molecules with narrow Δ E ST and efficient ISC; – also, in many D–A-type luminophores, RTP and TADF coexist with a tunable luminescent ratio due to the high sensitivity and stimuli-responsive characteristics of D–A structures to the external environment .…”

“…Organic semiconductors containing conjugated chemical structures with significant advantages compared to their inorganic counterparts have experienced explosive development in various fields of optoelectronic devices. – To develop high-performance organic semiconductors, the donor (D)–acceptor (A) molecular architecture has emerged as a flexible and efficient approach to tuning frontier molecular orbitals, , band gaps, , charge transport properties, , excited-state energies, , etc. Consequently, the D–A-type molecules have been widely recognized to construct not only ambipolar materials but also various emitters including fluorescent dyes, , phosphors, , thermally activated delayed fluorescence (TADF) molecules, , and room-temperature phosphorescence (RTP) materials. – The multifunctionality of the D–A structure is closely related to the unique electronic communications between D and A units that can be facilely manipulated by diverse strategies to achieve the desired performance. , Generally, the D–A molecules show both the locally excited (LE) state dominated by D and/or A units and the intramolecular charge-transfer (ICT) state owing to the charge transfer from the electron-rich D moiety to the electron-deficient A unit. , Impressively, the D–A architecture can massively reduce the singlet–triplet splitting energy (Δ E ST ) to benefit efficient intersystem crossing (ISC) to populate triplet excited states for RTP and reverse ISC for TADF. , Moreover, the wide availability of both A and D building blocks as well as diversified linkages between them leave plenty of room for structural diversity in the molecular design of organic semiconductors with expected functionality, compatibility, stability, and other features for the advanced applications. , …”

Reducing intersystem crossing rates of boron emitters for high-efficiency and long-lifetime deep-blue OLEDs

“…Boron-based blue emitters have gained significant attention due to their narrow emission bandwidth, making them attractive for high color purity OLEDs. [38][39][40][41][42][43][44][45][46][47][48][49][50] While the research studies on boron emitters have mainly focused on the promotion of device efficiency through the TADF characteristics, the development of boron-based emitters for F-OLEDs is extremely scare. [51][52][53][54] Currently, it remains unclear what kind of organic blue emitters can simultaneously achieve high efficiency, high color purity and long operational lifetime in F-OLEDs.…”