Tuning Hybridized Local and Charge-Transfer Mixing for Efficient Hot-Exciton Emission with Improved Color Purity

Abstract

Delayed fluorescence (DF) emitters with high color purity are of high interest for applications in high-resolution displays. However, the charge transfer required by high emitting efficiency usually conflicts with the expected color purity. In this work, we investigated the S1/S0 conformational relaxation, spin–orbital coupling (SOC), and vibronic coupling of hot-exciton emitters while hybrid local and charge transfer (HLCT) state tuning was achieved by a structural meta-effect. The meta-linkage leads to suppressed S1/S0 conformational relaxation and weakened vibronic coupling, while the unsacrificed emitting efficiency is largely ensured by multiple rISC channels (T n → S m ) with thermally accessible triplet–singlet energy gap (ΔE ST) and effective SOC. We demonstrated that the unique excited-state mechanism provides opportunities to improve the emitting color purity of hot-exciton emitters without sacrificing emitting efficiency by HLCT state tuning with simple chemical structural modification, for which hot-exciton emitters might play a more important role for high-resolution organic light-emitting diode displays.

Ultrafast photophysics of an orange–red thermally activated delayed fluorescence emitter: the role of external structural restraint

“…51,52 By further conrming the CT/LE nature of lowlying singlet/triplet states through natural transition orbital (NTO) analysis (Fig. S4 and S5 †) and hole-electron analysis (Table S4 †), 53,54 the T 1 / S 1 ( 3 LE D/A / 1 CT DA ) transition was assigned as the accessible RISC channel that is responsible for the delayed uorescence of TDBA-Ac and PzTDBA.…”

Accelerating Intersystem Crossing in Multiresonance Thermally Activated Delayed Fluorescence Emitters via Long-Range Charge Transfer

“…Besides, the results are similar to the corresponding calculations of the optimized geometries of S 1 and T 1 states (Table S4). Many previous studies focusing on the rational design of TADF emitters have shown that high-lying excited states may open additional channels to ISC or RISC processes via hybrid-localized charge transfer (HLCT), − hot exciton, − or vibronic coupling , to balance the singlet and triplet exciton populations to improve the electroluminescence performance. Therefore, we expect that the ISC processes in TSBA-Cz and TSBA-PhCz will be appropriately accelerated relative to TSBA when the high-lying LRCT state is involved in the spin-flip process.…”

Weak-conjugation linked donor–acceptor emitters for efficient near-ultraviolet organic light-emitting diodes with narrowed full width at half maximum

“…[17][18][19][20][21][22][23][24] In addition, the links between the donor and acceptor often play a key role for emitters. [25][26][27][28][29][30][31][32][33][34] A link with a conjugation or nonconjugation method between the donor and acceptor, such as ortho-, meta-, and para-positions in a benzene ring, can finely modulate the electronic states and the emission wavelength. Compared to the para-position conjugation, meta-position conjugation often provides blue-shifted emission due to the weaker D-A interaction, while the ortho-position conjugation can effectively alter the electronic structure by the twisting effect, especially for molecules with large D and A groups.…”