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Organic fluorescent emitters with narrowband emissions are highly desirable for high‐resolution organic light‐emitting diode (OLED) display technology. In principle, this can be achieved by specifically controlling the intrinsic structural relaxation and vibronic coupling in the excited state. Here, a design strategy to realize narrowband emission of organic fluorescent emitters is proposed by significantly enhancing the low‐frequency vibronic coupling strength (Λ) while simultaneously reducing the high‐frequency Λ of the commonly involved stretching modes. The quinolino‐[3,2,1‐de]acridine‐5,9‐dione (QAO) species is found to be directly associated with this design principle. By introducing single bond‐linked peripheral moieties into the QAO core, the constructed QAO derivatives are shown to exhibit better performance, by achieving a full width at half‐maximum of 23 nm/0.13 eV in toluene for the narrowest band as well as 27 nm/0.15 eV in doped devices, with negligible dependence on the doping concentrations. The maximum external quantum efficiency of the fabricated blue OLED is 17.5%. [ABSTRACT FROM AUTHOR]

Excited state characters and components play a decisive role in photoluminescence (PL) and electroluminescence (EL) properties of organic light-emitting materials (OLEDS). Charge-transfer (CT) state is beneficial to enhance the singlet exciton utilizations in fluorescent OLEDs by an activated reverse intersystem crossing process, due to the minimized singlet and triplet energy splitting in CT excitons. However, the dominant CT component in the emissive state significantly reduces the PL efficiency in such materials. Here, the strategy is to carry out a fine excited state modulation, aiming to reach a golden combination of the high PL efficiency locally emissive (LE) component and the high exciton utilizing CT component in one excited state. As a result, a quasi-equivalent hybridization of LE and CT components is obtained in the emissive state upon the addition of only an extra phenyl ring in the newly synthesized material 4-[2-(4′-diphenylamino-biphenyl-4-yl)-phenanthro[9,10-d]imidazol-1-yl]-benzonitrile (TBPMCN), and the nondoped OLED of TBPMCN exhibited a record-setting performance: a pure blue emission with a Commission Internationale de L'Eclairage coordinate of (0.16, 0.16), a high external quantum efficiency of 7.8%, and a high yield of singlet exciton of 97% without delayed fluorescence phenomenon. The excited state modulation could be a practical way to design low-cost, high-efficiency fluorescent OLED materials. [ABSTRACT FROM AUTHOR]

In contrast to the common intramolecular charge transfer (ICT) emission, planarized intramolecular charge transfer (PLICT) based materials usually possess higher proportion radiative decay for their flat and rigid conformation in excited states. Herein, a strategy for designing PLICT‐based emitters by the excited state quinone‐conformation induced planarization is proposed. By virtue of RIR mechanism on TPP (tetraphenylpyrazinyl) unit, the newcomers named as TPP‐PPI (1‐phenyl‐2‐(4′‐(3,5,6‐triphenylpyrazin‐2‐yl)‐[1,1′‐biphenyl]‐4‐yl)‐1H‐phenanthro[9,10‐d] imidazole) and TPP‐PI (1‐phenyl‐2‐(4‐(3,5,6‐triphenylpyrazin‐2‐yl)phenyl)‐1H‐phenanthro[9,10‐d]imidazole) exhibit aggregation‐induced emission (AIE) characteristics. TPP‐PPI and TPP‐PI have obvious PLICT properties via series of spectral measurements. Employing theoretical calculation in ground and excited states in different solvents, their PLICT process is confirmed further, and TPP's contribution on PLICT formation becomes clear. In non‐doped organic light‐emitting diodes, these two emitters with AIE and PLICT characteristic exhibit good performance with external quantum efficiency (4.85% and 4.36%) as blue emitters. [ABSTRACT FROM AUTHOR]