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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]

Thermally Activated Delayed Fluorescent (TADF) molecules with Donor (D) -Acceptor (A) –Donor-Acceptor π-Conjugated Macrocycle structures have broad application potential in organic light-emitting diodes. In this paper, three D−A line type and one D−A−D−A π‑Conjugated Macrocycle molecules with same donor and acceptor groups are investigated using polarizable continuum model (PCM) combined with density functional theory (DFT) and time-dependent functional theory (TD-DFT) in solvent and film. It is found that the macrocyclic structure has a smaller energy gap (ΔEST) between the first singlet excited state (S1) and the first triplet excited state (T1) than the linear structure. The TADF property is also analyzed based on the calculation of spin–orbit coupling (SOC) and the (reverse) intersystem crossing (RISC) rates between S1 and T1. The macrocyclic molecules have larger SOC and faster RISC rates, which also well explains the experimental predictions and results. [Display omitted] • The macrocyclic structure has smaller △ES1-T1 as compared to the linear structure. • The macrocyclic molecules have larger SOC and faster RISC rates, which also well explains the experimental predictions and results. • Compared to the linear structure, the macrocyclic structure has a smaller reorganization energy and H-R factor. Thermally Activated Delayed Fluorescent (TADF) molecules with Donor (D) -Acceptor (A) –Donor-Acceptor π-Conjugated Macrocycle structures have broad application potential in organic light-emitting diodes. In this paper, three D − A line type and one D − A − D − A π‑Conjugated Macrocycle molecules with same donor and acceptor groups are investigated using polarizable continuum model (PCM) combined with density functional theory (DFT) and time-dependent functional theory (TD-DFT) in solvent and film. It is found that the macrocyclic structure has a smaller energy gap (ΔE ST) between the first singlet excited state (S 1) and the first triplet excited state (T 1) than the linear structure. The TADF efficiency is also analyzed based on the calculation of spin–orbit coupling (SOC) and the (reverse) intersystem crossing (RISC) rates between S 1 and T 1. The macrocyclic molecules have larger SOC and faster RISC rates, which also well explains the experimental predictions and results. [ABSTRACT FROM AUTHOR]

In this work, we systematically study the photo physical properties for NIR-AIE-TADF molecules in toluene solvent, film and crystal by PCM and QM/MM method, respectively. First, the molecular luminescence was red-shifted by about 100 nm, when –CH3 in the molecule is replaced by –OCH3, which may be due to the increased vibrational intensity of the molecule, resulting in energy dissipation. Second, the vibrations were effectively suppressed in the solid state for both TBSMCN and O-TBSMCN molecules, which is the reason for the AIE of the molecules. Third, the molecules have a small △ES1-T1 in the solvent with TADF properties, and their △ES1-T1 is reduced and SOC is increased in the solid state, which is more favorable for the RISC. Fourth, by analyzing the nature of the transitions in the dimers in the film structure we find that O-TBSMCN molecule undergoes intermolecular charge transfer, which may be one of the reasons for its reduced film efficiency. [Display omitted] • The inhibition of vibration in the aggregated state is the main reason for AIE. • A smaller △E S1-T1 and a larger SOC in aggregate state, it is favorable for RISC. • The O-TBSMCN molecule undergoes intermolecular CT, which lower its film efficiency. TADF emitters with both high exciton utilization and luminescence efficiency show promising applications in OLEDs, especially it with AIE characteristics. However, theoretical studies on emitters with amorphous structure with the consideration of the solid-state effect are limited. In this work, a multi-scale simulation is performed to study the reported compounds TBSMCN and O-TBSMCN, which both possess distinct features of NIR-AIE-TADF. The packing modes of the molecules in film and crystal are obtained by molecular dynamics simulations (MD) and experiments, and then the photo physical properties are studied by using the QM/MM method. The results show that geometrical changes between the ground state (S 0) and the first singlet excited state (S 1) are restricted in aggregate state. Thus, the non-radiative energy consumption process is hindered, this indicates the AIE mechanisms. Second, the molecules exhibit a smaller △E S1-T1 and a more significant SOC in aggregate state, which is more favorable for the RISC. Finally, by analyzing the NTO of the dimers in the film, the O-TBSMCN molecule undergoes intermolecular charge transfer, which may be one of the reasons for the significant reduction in its film efficiency. Our calculations could help one to better understand the NIR-AIE-TADF mechanism from a theoretical perspective. [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 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]

[Display omitted] • The materials with the HLCT state can break the limitation of the spin statistics. • The HLCT state is formed by re-interaction of the intrinsic LE state and CT state. • The LE and CT states with small ΔE and large J will be combined linearly. • In a molecular system with multiple identical D and A, a new CT state will be formed. Hybridized local and charge-transfer excited state (HLCT) is an excited state formed by the re-interaction of the intrinsic locally-excited (LE) state and charge-transfer (CT) state. In this paper, a donor–acceptor (D-A) molecule TPA-Nz is used as a benchmark to analyze the formation of the HLCT state. By changing the number of the D or A, the excited state energy and properties are summarized. We found that in a molecular with multiple donors or acceptors, the excited state formed can be divided into three types. If the energy of the intrinsic LE state is lower than the CT state, the HLCT state dominated by the LE state will be in the lowest energy, the HLCT state dominated by the CT state will be in the higher energy, and new CT state will be formed in the highest part. The number of new-formed excited state is equal to the number of acceptor. [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]

Organic luminophores of narrowband emission are considered a filter-less light resource, promising for high-resolution organic light-emitting diode (OLED) display technology. It is essentially feasible to achieve narrowband emission by manipulating the intrinsic structural relaxation and vibronic coupling in the excited state. On this basis, by the introduction of single bond-linked peripheral moieties of 4-methoxyphenyl into the benzo[c]benzo [7,8]quinolino[1,2,3-fg]acridine-7,11-dione (BAO) core, the resulting BAO-PMO is observed to exhibit better performance, achieving a full width at half-maximum (FWHM) of down to 27 nm/0.14 eV in toluene for the narrowest band compared with that of BAO (35 nm/0.20 eV). An effective strategy is thus proposed by the significant enhancement of the low-frequency vibronic coupling strength with simultaneous mitigation of the high-frequency ones to realize the control of structural relaxation. In consequence, the BAO-PMO based OLED device exhibits a narrowband green emission with an FWHM of 37 nm/0.18 eV. • Organic narrowband luminophores based on carbonyl-bridged triarylamine were shown. • The emission narrowing was achieved via vibronic coupling regulation of the excited-state configuration. • Doped OLEDs exhibit narrowband green emission with a full width at half-maximum of down to 37 nm. [ABSTRACT FROM AUTHOR]

In this work, we report two isomers composed of 1-phenyl-1 H -phenanthro[9,10 -d ]imidazole (PI), hydroxyl and tetraphenylethylene (TPE), abbreviated as m -PITPE and p -PITPE. It is found that they exhibit similar aggregation-induced emission (AIE) behavior but totally different excited-state intramolecular proton transfer (ESIPT) characteristic, as a result of the different linkage sites of PI on TPE moiety. Theoretical calculations and their different experimental responses to F− demonstrate that only the para -linkage isomer displays ESIPT. In m -PITPE with meta -linkage, the electron cloud distribution only locates at the TPE part in the singlet excited (S 1) states, which results in the localized excited state without ESIPT characteristic. Image 1 [ABSTRACT FROM AUTHOR]

Deep red (DR) and near-infrared (NIR) fluorescent emitters are often plagued by design difficulties due to the strong intramolecular interaction. Herein, two new DR and NIR molecules, 4-(7-(10-ethyl-10 H -phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)- N,N -diphenylaniline (TPAC2) and 4-(9-(10-ethyl-10 H -phenoxazin-3-yl)naphtho[2,3-c][1,2,5]thiadiazol-4-yl)- N,N -diphenylaniline (TPANZC2), characteristic with hybrid local and charge transfer were achieved via iteration with a theoretical combined experimental method. Both emitters realized the reverse intersystem crossing (RISC) via the hot exciton channel. As results, the non-doped organic light-emitting diodes (OLEDs) of TPAC2 and TPANZC2 achieved the maximum external quantum efficiency (EQE max) of 2.4% at 680 nm and 1.1% at 755 nm, respectively. Both conspicuous upward EQE curves demonstrated excellent resistance to efficiency roll-off. The ternary co-doping system further unleashed the potential in NIR emission, the co-doped device with 5 wt% TPANZC2 achieved an EQE of 4.6% with emission at 724 nm, which is among the best results of HLCT-NIR fluorescent OLEDs to date. [Display omitted] • Iterative strategy reasonably achieved deep red to NIR emission. • The co-doped NIR device achieved an EQE of 4.6%, is the best HLCT-NIR OLED performance to date. • EQE loss only 2.4% and 0.8% at 90% maximum luminescence. [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]

In this work, a novel green emitter, namely 16,16-dimethylbenzo[ a ]quinolino[3,2,1- de ]acridin-10(16 H)-one (GACQ), with amine‒carbonyl fused structure has been designed and synthesized. The single-crystal structure analysis confirmed that the fused structure shows non-planar conformation with dihedral angle of 48.97° from the front-view direction. The photophysical and theoretical results confirmed that GACQ exhibited hybridized local and charge-transfer (HLCT) feature with strong green emissions of 513 and 535 nm in solution and film, respectively. The non-doped device based on GACQ achieved high luminance (15810 cd m−2) and good efficiency stability with negligible external quantum efficiency (EQE) roll-off. Furthermore, the doped device exhibited high maximum EQE of 4.8% with CIE coordinate of (0.38, 0.58). [Display omitted] • A novel amine‒carbonyl fused emitter, GACQ, has been successfully constructed. • GACQ possesses hybridized local and charge-transfer characteristic. • Non-doped device of GACQ exhibited high luminance and negligible EQE roll-off. • Doped device based on GACQ achieved maximum EQE of up to 4.8%. [ABSTRACT FROM AUTHOR]

This work provides a flexible and convenient method for fine-tuning the excited states of emitters, precise "surgery" was performed by targeting the molecular excited states through locally large twisted conformations, and finally obtained excellent hot exciton red emitters and high efficiency non-doped deep-red OLEDs. [Display omitted] • Deep-red emitters construct idea utilizing locally large twisted conformation. • Three emitters display hot exciton and aggregation-induced emission properties. • Breakthrough EQEs of hot exciton non-doped red devices up to 5.3% and 6%. The precise regulation of excited state is a challenge to emitters for achieving highly efficient non-doped deep-red electroluminescence (EL). Herein, we used triphenylamine and phenoxazine as donors and benzo[c][1,2,5]thiadiazole as an acceptor to construct a hot exciton skeleton. Then chemically modified the phenoxazine by locally large twisted conformation to obtain N , N -diphenyl-4-(7-(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)aniline (TPAPH), 4-(7-(10-(4-ethoxyphenyl)-10 H -phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)- N , N -diphenylaniline (TPAPHOC2), and 4-(3-(7-(4-(diphenylamino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-10 H -phenoxazin-10-yl)benzonitrile (TPAPHCN), thereby achieving excited state perturbation. As a result, three emitters exhibited aggregation-induced emission enhancement and hybridized local and charge transfers characteristics based on photophysical experimentals. In EL, the TPAPH-, TPAPHOC2-, and TPAPHCN-based non-doped devices achieved deep-red emission with Commission International de L'Eclairage coordinates of (0.68, 0.32), (0.69, 0.31), and (0.66, 0.34) and with emission peaks at 660, 669, and 647 nm, respectively. The maximum external quantum efficiencies were 5.3%, 3.7%, and 6.0%, respectively. The results of this study not only realize the non-doped deep-red OLEDs with high performance but also indicate that the presence of locally large twisted conformation presented an efficient manner for exploring precise excited state tuning for fluorescent emitter. [ABSTRACT FROM AUTHOR]