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A new hybrid local and charge transfer (HLCT) molecule 2TPA‐PPI is obtained for constructing the high‐performance organic light‐emitting diodes (OLEDs) in this work. 2TPA‐PPI possesses the sufficient emission/charge‐transporting properties, thus it is used as a neat emitter achieving an efficient deep‐blue OLED with very high external quantum efficiency (EQE) up to 10.7%, as well as a multi‐functional emitting host matrix constructing the high‐performance phosphorescent OLEDs. More importantly, a high‐efficiency candle light‐style OLED adopting the HLCT/phosphor hybrid strategy is realized, where 2TPA‐PPI acts as not only a blue emitter, but also a universal host sensitizing both yellow and red phosphors. This quasi‐white OLED represents almost the highest EQE/PE level of 25.2%/49.7 lm W−1 at the practical luminance level of 1000 cd m−2 for the white OLEDs with the excellent color rendering index values of more than 80 reported. [ABSTRACT FROM AUTHOR]

The excited state properties of organic fluorescent materials are crucial for their photoelectronic performance. Here, a study on the highly efficient electrofluorescent material 4-(2-(4′-(diphenylamino)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)benzonitrile (TBPMCN) is carried out, focusing mainly on its crystal structure and photophysical properties under pressure stimulation. The special triangular-cone (TC) configuration of triphenylamine group in TBPMCN crystal exhibits charge-transfer (CT)-dominated excited state property in TBPMCN, which gives rise to a blue-shifted emission in the crystal. Theoretical calculations prove that the TC conformation is a dynamically metastable state, which is higher in energy than the three-blade-propeller (TBP) configuration. In a further piezochromic experiment, a unique rehybridization-induced emission enhancement phenomenon is found in this crystal, which is essentially different from the aggregation-induced emission enhancement (AIEE) mechanism. It can be assigned to the change of excited state property from a CT-dominated state to a hybridized locally excited and charge-transfer state, as a result of the rehybridization of nitrogen atom upon the increased external pressure. This work provides deep insight into the relationship between molecular structure and excited state properties in crystal by means of the pressure stimulation and further enriches the AIEE mechanism. Additionally, the large red-shifted piezochromic phenomenon of this CT material is stressed. [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]

A multifunctional AIE-active molecule, CzPySiTPE, in which carbazole (Cz) and pyridine (Py) were attached to tetraphenylsilane to facilitate carrier injection has been designed and synthesized. Tetraphenylethene (TPE) was adopted to maintain efficient blue emission. Blue electroluminescent (EL) emission of CzPySiTPE was obtained with CIE coordinates of (0.16, 0.17) and an external quantum efficiency of 1.12 %. [ABSTRACT FROM AUTHOR]

In principle, the ratio (Φ) of the maximum quantum efficiencies for electroluminescence (EL) to photoluminescence (PL) can be expected to approach unity, if the exciton (bound electron-hole pair) generated from the recombination of injected electrons and holes in OLEDs has a sufficiently weak binding energy. However, seldom are examples of Φ > 25% reported in OLEDs because of the strongly bound excitons for most organic semiconductors in nature. Here, a twisting donor-acceptor triphenylamine-thiadiazol molecule (TPA-NZP) exhibits fluorescent emission through a hybridized local and charge-transfer excited state (HLCT), which is demonstrated from both fluorescent solvatochromic experiment and quantum chemical calculations. The HLCT state possesses two combined and compatible characteristics: a large transition moment from a local excited (LE) state and a weakly bound exciton from a charge transfer (CT) state. The former contributes to a high-efficiency radiation of fluorescence, while the latter is responsible for the generation of a high fraction of singlet excitons. Using TPA-NZP as the light-emitting layer in an OLED, high Φ values of 93% (at low brightness) and 50% (at high brightness) are achieved, reflecting sufficient employment of the excitons in the OLED. Characterization of the EL device shows a saturated deep-red emission with CIE coordinates of (0.67, 0.32), accompanied by a rather excellent performance with a maximum luminance of 4574 cd m−2 and a maximum external quantum efficiency (ηext) of ∼2.8%. The HLCT state is a new way to realize high-efficiency of EL devices. [ABSTRACT FROM AUTHOR]

The development of near‐infrared (NIR) organic light‐emitting diodes (OLEDs) is of growing interest. Donor–acceptor (D–A) chromophores have served as an important class of NIR materials for NIR OLED applications. However, the external quantum efficiencies (EQEs) of NIR OLEDs based on conventional D–A chromophores are typically below 1 %. Reported herein is a butterfly‐shaped D–A compound, PTZ‐BZP. A PTZ‐BZP film displayed strong NIR fluorescence with an emission peak at 700 nm, and the corresponding quantum efficiency reached 16 %. Remarkably, the EQE of the NIR OLED based on PTZ‐BZP was 1.54 %, and a low efficiency roll‐off was observed, as well as a high radiative exciton ratio of 48 %, which breaks through the limit of 25 % in conventional fluorescent OLEDs. Experimental and theoretical investigations were carried out to understand the excited‐state properties of PTZ‐BZP. [ABSTRACT FROM AUTHOR]

Deep blue luminescent materials play a crucial role in the organic light-emitting diodes (OLEDs). In this work, a novel deep blue molecule based on hybridized local and charge-transfer (HLCT) excited state was reported with the emission wavelength of 423 nm. The OLED based on this material achieved high maximum external quantum efficiency (EQE) of 4% with good color purity. The results revealed that the locally-excited (LE)-dominated HLCT excited state had obvious advantages in short wavelength and narrow spectrum emission. What is more, the experimental and theoretical combination was used to describe the excited state characteristic and to understand photophysical property. [ABSTRACT FROM AUTHOR]

The properties of excited states of emitters play an important role in OLEDs. How to obtain balanced hybrid localized charge transfer (HLCT) state by reasonably designing molecules is still a challenge. Herein, three HLCT states D-π-A type blue fluorophores with different LE/CT hybrid degree were designed and synthesized, namely 3,6-di-tert-butyl-9-(4-(6-(4-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)phenyl)pyren-1-yl)phenyl)-9 H carbazole (DTPCZPYTZ), 3,6-di-tert-butyl-9-(4-(4-(4-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)phenyl)naphthalen-1-yl)phenyl)-9 H -carbazole (DTPCZNATZ) and 3,6-di-tert-butyl-9-(4''-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)-[1,1':4′,1″-terphenyl]-4-yl)-9 H -carbazole (DTPCZPHTZ). DTPCZPHTZ achieved quasi-equivalent hybrid local and charge-transfer (HLCT) excited state and efficient "hot-exciton" channel, the non-doped deep-blue device based on DTPCZPHTZ has an electroluminescence emission peak (λ EL) of 427 nm with Commission International de L'Eclairage (CIE) of (0.157, 0.037), the maximum external quantum efficiency (EQE) is up to 5.7% and the efficiency roll-off is only 5% (under 1000 cd m−2), which is outstanding in the reported deep-blue emitters. This study proved that the quasi-equivalent hybrid HLCT state is beneficial to improving device performance. This work provides a flexible and convenient method for fine-tuning the excited states of emitters, by changing the number of benzene rings in the intermediate π bridge, the degree of LE/CT hybridization can be adjusted. Finally, quasi-equivalent hybrid deep-blue luminescent emitter and highly efficient non-doped deep-blue OLED is obtained. [Display omitted] • Construction of quasi-equivalent hybrid local and charge-transfer (HLCT) excited state and hot exciton channels. • Efficient non-doped deep-blue OLED with EQE up to 5.7% and CIE (0.157, 0.037). • Highly Suppressed efficiency roll-off of only 1%–5% at 1000 cd m−2. [ABSTRACT FROM AUTHOR]