Mechanical Insights into Aggregation‐Induced Delayed Fluorescence Materials with Anti‐Kasha Behavior

Abstract

Organic materials with aggregation‐induced delayed fluorescence (AIDF) have exhibited impressive merits for improving electroluminescence efficiency and decreasing efficiency roll‐off of nondoped organic light‐emitting diodes (OLEDs). However, the lack of comprehensive insights into the underlying mechanism may impede further development and application of AIDF materials. Herein, AIDF materials consisting of benzoyl serving as an electron acceptor, and phenoxazine and fluorene derivatives as electron donors are reported. They display greatly enhanced fluorescence with increased delayed component upon aggregate formation. Experimental and theoretical investigations reveal that this AIDF phenomenon can be rationally ascribed to the suppression of internal conversion and the promotion of intersystem crossing in solid. Moreover, the theoretical calculations disclose that the efficient solid‐state delayed fluorescence originates from the higher energy electronic excited state (e.g., S2) rather than the lowest energy‐excited state (S1), demonstrating an anti‐Kasha behavior. The excellent AIDF property allows high exciton utilization and thus superb performance of OLEDs using these new materials as light‐emitting layers.

Through-Space Conjugation: A Thriving Alternative for Optoelectronic Materials

“…This result demonstrates the feasibility of nondoped OLEDs with brilliant performance by applying AIDF materials, and many other breakthroughs have been achieved in different AIDF systems. [37][38][39][40][41][42][43][44] Unlike the molecules discussed above with π-conjugated backbones that allow the coexistence of through-space and through-bond conjugation, a new type of polymer, P-Ac(1-x)-TRZx, 45 comprised of a saturated hydrocarbon backbone and aromatic electron donors and acceptors as pendants (Figure 3a), possesses only through-space conjugation yet exhibits an interesting blue TADF property. The saturated hydrocarbon backbone avoids the strong electronic coupling between donors and acceptors to achieve blue emission and a small ΔE ST .…”

De novo strategy with engineering anti-Kasha/Kasha fluorophores enables reliable ratiometric quantification of biomolecules

“…As an important principle in photochemistry to most fluorophores, Kasha's rule states that fluorophores can only generate one emission band from the lowestenergy excited singlet state (S 1 ), irrespective of the excitation wavelength 26 . In contrast, anti-Kasha dyes remain exceedingly rare [27][28][29][30][31][32] , and most of them emit in the short wavelength region and are thus not suitable for biological applications 33 . Moreover, to the best of our knowledge, the modulation of anti-Kasha emission for ratiometrically detecting bioanalytes has yet to be demonstrated.…”

Efficient Aggregation-Induced Delayed Fluorescence Luminogens for Solution-Processed OLEDs With Small Efficiency Roll-Off

“…In the aggregated state, however, the intramolecular motions are greatly suppressed by spatial hindrance, and the IC channel is blocked. Therefore, given their small E ST values, the ISC and RISC are able to occur, leading to noticeable delayed fluorescence (Guo et al, 2018(Guo et al, , 2019.…”

“…Recently, by taking the advantages of aggregation-induced emission (AIE) and TADF, a new molecular design strategy of aggregation-induced delayed fluorescence (AIDF) was proposed and a series of novel luminogens based on AIDF were developed. These AIDF materials could not only harness both singlet and triplet excitons, but also showed the merit of very small efficiency roll-off at high luminance (Huang et al, 2017;Guo et al, 2018Guo et al, , 2019.…”