Aggregation-caused quenching (ACQ) has long been a problem that inhibits the application of organic light-emitting materials in organic light-emitting diodes, especially near-infrared (NIR) materials. Figuring out the reasons that induce ACQ is important for the quantum efficiency enhancement of NIR materials. In this paper, an NIR molecule (TPA-QCN) with thermally activated delayed fluorescence (TADF) is studied based on first-principles calculations and excited-state dynamics investigation in both toluene and in the aggregation state. Our calculation indicates that aggregation can induce a smaller energy gap between the first singlet excited state and the first triplet excited state, which is favorable for TADF. Both the decreased fluorescent rate and the increased nonradiative rate will induce emission quenching in the aggregation state. Based on detailed analyses of the reorganization energy and intermolecular interaction, we find that the hydrogen bond will induce enhanced contribution to the reorganization energy from C–H stretching vibration modes and thus a larger nonradiative rate in the aggregation state than in toluene. A new mechanism of ACQ is proposed, and it could help in the design of new types of NIR-TADF molecules with enhanced fluorescence efficiency.

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.

Near-infrared (NIR) thermally activated delayed fluorescence (TADF) materials have shown great application potential in organic light-emitting diodes, photovoltaics, sensors, and biomedicine. However, their fluorescence efficiency (ΦF) is still highly inferior to those of conventional NIR fluorescent dyes, seriously hindering their applications. This study aims to provide theoretical guidance and experimental verification for highly efficient NIR-TADF molecular design. First, the light-emitting mechanism of two deep-red TADF molecules is revealed using first-principles calculation and the thermal vibration correlation function (TVCF) method. Then several acceptors are theoretically designed by changing the position of the cyano group or by introducing the phenanthroline into CNBPz, and 44 molecules are designed and studied theoretically. The photophysical properties of DA-3 in toluene and the amorphous state are simulated using a multiscale method combined with the TVCF method. The NIR-TADF property for DA-3 is predicted both in toluene and in the amorphous state. Experimental measurement further confirms that the TADF emission wavelength of DA-3 is 730 nm and ΦF is as high as 20%. It is the highest fluorescence efficiency reported for TADF molecules with emission wavelengths larger than 700 nm in toluene. Our work provides an effective molecular design strategy, and a good candidate for highly efficient NIR-TADF emitters is also predicted.

Investigation about the excited state properties to reveal the AIE and TADF mechanisms using a QM/MM method.

Synergism between covalent and non-covalent bonds is employed to fix an organic phosphor guest in a rigid inorganic framework, simulating the stiffening effect seen in the glassy state and realizing efficient and ultralong roomtemperature phosphorescence (RTP). Twelve heavy-atom-free composites have been obtained through introducing arylboric or arylcarboxylic acid derivatives into the inorganic boric acid matrix by solid-phase synthesis. Owing to the stiffening effect of multiple bonds, all the composites show highly efficient and persistent RTP of guest molecules with a quantum yield ranging from 39.8 % to ca. 100 % and a lifetime up to 8.74 s, which results in a 55 s afterglow visible to the naked eye after exposure to a portable UV lamp. Interestingly, it is found that the substitution position and quantity of carboxyl in the guest have a great influence on the phosphorescent properties, and that the heavy-atom effect is invalid in such host-guest hybrid systems. The 100 g grade composite is easily prepared because of the solvent-free, green, and simple synthesis method. These results provide an important way for the development of RTP materials with ultrahigh quantum yield and ultralong lifetime, as well as their practical applications in the fields of anti-counterfeiting and information storage, among others.