Establishing a simple and versatile design strategy to finely modulate emission colors while retaining high luminescence efficiency and color purity remains an appealing yet challenging task for the development of multi‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) materials. Herein, we demonstrate that the strategic introduction of electron‐withdrawing imine and electron‐donating amine moieties into a versatile boron‐embedded 1,3‐bis(carbazol‐9‐yl)benzene skeleton enables systematic hypsochromic and bathochromic shifts of narrowband emissions, respectively. By this method, effective electroluminescence color tuning was accomplished over a wide visible range from deep‐blue to yellow (461–571 nm), using the same MR molecular system, without compromising very narrow spectral features. Deep‐blue to yellow organic light‐emitting diodes with maximum external quantum efficiencies as high as 19.0–29.2 % and superb color purity could be produced with this family of color‐tunable MR‐TADF emitters.

Thermally activated delayed fluorescence (TADF) materials generate energetically equivalent spin-singlet and spin-triplet excited states. In the presence of an energy acceptor, each excited state undergoes energy transfer on different length scales. However, the lack of quantitative understanding of the length dependence of the excited energy-transfer processes hampers the rational design of molecular systems that control exciton transport in organic light-emitting diodes (OLEDs) using TADF. We herein utilize a dendritic fluorophore G1, which consists of an anthracene-based fluorescent core encapsulated by four insulating tris(4-tert-butylphenyl)methyl groups as an energy acceptor. By combining transient photoluminescence measurements and kinetic modeling, we demonstrate the spin-dependent energy transfer in a binary host−guest system composed of a TADF material as the exciton-harvesting host and G1 as the guest fluorophore. The encapsulated structure with the dendritic shell effectively inhibits triplet excitons on the TADF host from funneling to the fluorescent core, thus allowing efficient reverse intersystem crossing and singlet energy transfer. The utilization of G1 in solution-processed OLEDs leads to a maximum external electroluminescence quantum efficiency as high as 5.2%, which is equivalent to an enhancement by a factor of 1.6 over the corresponding nondendritic fluorophore.

A versatile design of thermally activated delayed fluorescence (TADF) π‐conjugated macrocycles incorporating electron‐donor (D) and acceptor (A) units into a cyclo‐meta‐phenylene motif with an alternating pattern is presented. The new π‐conjugated macrocycle, which combines three 5‐(N‐carbazolyl)‐phenylen‐1,3‐diyl as D units and three 6‐phenyl‐1,3,5‐triazin‐2,4‐diyl as A units, possesses a small singlet–triplet energy gap and hence can emit efficient green TADF both in solution and doped thin films. Comparative experimental and computational investigations of the electronic and photophysical properties of the macrocycle with its analogous noncyclic compound reveal key advantages of the cyclic molecular configuration for actual emitters. Organic light‐emitting diodes incorporating the TADF π‐conjugated macrocycle as an emitter demonstrate high external electroluminescence quantum efficiencies of up to 15.7%, outperforming the devices based on the noncyclic emitter. Herein, the importance of geometric design for producing novel organic emitters with fascinating optoelectronic and morphological characteristics is highlighted.

Establishing a simple molecular design strategy for enabling redshifted emissions while maintaining high color purity in multi-resonance thermally activated delayed fluorescence (MR-TADF) remains a crucial yet challenging task. Herein, we...

Establishing a simple and versatile design strategy to finely modulate emission colors while retaining high luminescence efficiency and color purity remains an appealing yet challenging task for the development of multi-resonanceinduced thermally activated delayed fluorescence (MR-TADF) materials. Herein, we demonstrate that the strategic introduction of electron-withdrawing imine and electrondonating amine moieties into a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton enables systematic hypsochromic and bathochromic shifts of narrowband emissions, respectively. By this method, effective electroluminescence color tuning was accomplished over a wide visible range from deep-blue to yellow (461-571 nm), using the same MR molecular system, without compromising very narrow spectral features. Deep-blue to yellow organic light-emitting diodes with maximum external quantum efficiencies as high as 19.0-29.2 % and superb color purity could be produced with this family of color-tunable MR-TADF emitters.