Electron-donating Units Research Articles

Quantifying Planarity in the Design of Organic Electronic Materials

AbstractPlanarity is essential for many organic electronic materials as it maximizes the intramolecular π‐orbital overlap and enables efficient intermolecular interactions through π‐stacking. We propose a statistical way of quantifying the planarity of a wide range of conjugated systems. The quantification takes into account all torsional conformations and their relative contribution to the overall structural disorder, through a planarity index ⟨cos2ϕ⟩. The propensity for planarization and the effect of rotational disorder were examined for a series of commonly used building blocks. The application of the analysis to extended conjugated systems and the correlations between the gas‐phase ⟨cos2ϕ⟩ and crystallographically observed planarity in the solid state were explored. Our calculations also reveal a previously unrecognized effect of increasing band gap upon planarization for conjugated systems coupling strong electron donor and acceptor units.

Wide bandgap donor polymers containing carbonyl groups for efficient non-fullerene polymer solar cells

Two wide bandgap conjugated polymers (PTCO8 and PTCO1) with different side chains, composed of alkylcarbonyl-substituted thiophene (TOC) as the electron-withdrawing unit and two-dimension benzodithiophene (BDT) as the electron-donating unit, are developed for non-fullerene polymer solar cells (PSCs). Relative to non-carbonyl-substituted control polymer PTC8, PTCO8 and PTCO1 exhibit a red-shifted absorption and deeper-lying highest occupied molecular orbital (HOMO) level. When blended with ITIC, the as-cast PTCO1-based devices yield a power conversion efficiency of up to 9.33% with an open-circuit voltage of 0.95 V, a short-circuit current density of 16.91 mA cm−2, and a fill factor of 57.9%, outperforming those of PTC8-based devices (4.04%) and PTCO8-based devices (5.91%). This work demonstrates that the carbonyl group is a promising electron-deficient moiety to construct wide-bandgap polymers for non-fullerene PSCs. Adjusting the length of side chains is a feasible strategy to improve PSC performance further.

Structure evolution from D-A-D type small molecule toward D-A-D-A-D type oligomer for high-efficiency photovoltaic donor materials

In order to study the influence of structure evolution on properties, a D-A-D-A-D-type oligomer of 5BDTBDD and its D-A-D type small molecule of 3BDTBDD were designed and synthesized, which consist of electron-accepting (A) unit of benzo [1,2-c:4,5-c'] dithiophene-4,8-dione (BDD) and electron-donating (D) unit of 4,8-di (6-ethylhexylthiophen-2-yl)benzo [1,2-b:4,5-b']dithiophene (BDT). The effect of structure evolution on crystallinity, absorption, mobility, morphology and photovoltaic properties was primarily investigated. It is found that, by simply inserting a D-A repeat unit, 5BDTBDD shows more improved crystallization, absorption, mobility and morphology than 3BDTBDD. As a result, 5BDTBDD exhibits better photovoltaic properties than 3BDTBDD in their non-fullerene organic solar cells using 9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis (4-hexylphenyl)-di thieno [2,3-d:2′,3′-d']-s-indaceno [1,2-b:5,6-b'] dithiophene (ITIC) as acceptor material. An increasing power conversion efficiency of 7.89% is obtained in the 5BDTBDD:ITIC cells, which is 1.8 times higher than that value (4.33%) in the 3BDTBDD:ITIC cells. It indicates that structure evolution from D-A-D type small molecule toward D-A-D-A-D type oligomer is an efficient strategy to achieve high-efficiency donor materials in organic solar cells.

Candle light-style OLEDs with benzochalcogenadiazoles cores

Fluorescent D-A1-π-A2 dyes containing the 9-hexyl-9H-carbazole electron-donor unit and 2,1,3-benzochalcogenadiazoles as electron-withdrawing, were synthesized. These dyes displayed high luminescence quantum yields up to 20% in the solid phase and 80% in solutions. A series of ClsOLEDs with high luminance up to 6256 cd/m2 and low color temperature (1800–1900 K) based on these dyes were constructed. The electroluminescence color temperature of the fabricated OLEDs is independent of the operating voltage making these compounds potentially very useful for night time illumination. It was shown that the aggregation process of the investigated dyes led to the formation of planar crystalline structures. Scanning electron microscopy (SEM) and fluorescence lifetime imaging (FLIM) experiments, showed that luminescence quenching caused by interactions between aggregates of different sizes takes place. Spectroscopic studies were supported by Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) calculations. As a result, we elucidated that replacement of [1,2,5]chalcogenadiazolo[3,4-c]pyridines by 2,1,3-benzochalcogenadiazoles led to a substantial improvement in intramolecular charge transfer (ICT) from the donor to acceptor units due to favourable distortion of the excited state geometry.

Synthesis, characterization and photophysical properties of π-conjugated novel phenothiazine substituted acrylonitrile D–A derivatives: Orange to red emission

• Phenothiazine substituted acrylonitrile derivatives are synthesized. • Optical band gap values range from 2.296 to 2.407 eV. • Measured experimental quantum yields ( φ) are range from 0.065 to 0.121. • The 5% weight loss temperatures of derivatives are in the range 170–250 °C. By utilizing palladium catalyzed Suzuki–Miyaura cross coupling reaction, a series of novel organic dyes containing phenothiazine were designed, synthesized (abbreviated as PTA-5(a–d)) in good yield and confirmed by spectroscopic methods. These bipolar dyes comprise of PTA moiety as the electron donor unit (D) and acrylonitrile as the electron acceptors/anchoring unit (A). By introducing substituents at C(3) and C(7) positions, Intramolecular Charge Transfer character of PTA was improved. Their photophysical/solvatochromic properties were examined with the assistance of DFT computations and the synthesized molecules exhibit red fluorescence with decent quantum yields. The computed and experimental results are found to be in accordance. Differential scanning calorimetry and thermogravimetric analysis showed the thermal stabilities of the compounds. The highest occupied molecular orbitals, lowest unoccupied molecular orbitals and energy band gap were computed with the help of frontier molecular orbitals. The outcome exhibit that the novel (D–A) chromophores could play important role in organic optoelectronics.

Photocatalytic Hydrogen Evolution Based on Nitrogen-Containing Donor–Acceptor (D–A) Organic Conjugated Small Molecules

Photocatalytic water splitting has attracted widespread attention as one of the eco-friendly technologies that can scalably produce low-cost renewable solar hydrogen. As a rare case, in this work, we apply organic conjugated small molecules to photocatalytic hydrogen evolution and compare the photocatalytic performance of CM1, CM2, and M1, whose number of N atoms is controlled by replacing the intramolecular electron donor unit with benzene, pyridine, and pyrazole, respectively. There is a clear correlation between the photocatalytic activity and the number of N atoms in the structure, as N atoms can be active sites for the photocatalytic interface reaction and help to improve the water dispersibility and contact of organic conjugated molecules through hydrogen-bonding interactions. In addition, we apply a single-atom substitution strategy (O, S, Se) to control the photoelectric properties of organic conjugated molecules. Among these molecules, M1 exhibits the best performance, even better than the previous series of polymers P2 and P4.

High-performance polymer solar cells based on terpolymer composed of one donor and two acceptors processed with non-halogenated solvent

Abstract Terpolymers consisting of three monomers with one electron donor unit and two electron acceptor units are promising p-type polymers for polymer solar cells (PSCs) because the incorporation of a third monomer into a copolymer backbone provides synergetic effect on physical properties such as absorption ability, charge transport, and photovoltaic performance. Currently, novel p-type terpolymers need to be developed for high-efficiency PSCs, which can be processed with eco-friendly non-halogenated solvents. In this study, a new series of terpolymers composed of 4,8-di(2,3-didecylthiophen-5-yl)-benzo[1,2-b:4,5-b′]dithiophene (BDT), 4,7-di(thien-2-yl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT), and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) segments was synthesized and characterized for high-performance PSCs processed with non-halogenated solvents. PBDTBD terpolymers (i.e., PBDTBD-25, PBDTBD-50, and PBDTBD-75) were synthesized by adjusting different ratios of DTffBT to BDD segment (25%, 50%, and 75% of DTffBT). PBDTBD terpolymers exhibited excellent solubility in non-halogenated solvents. The optical, electrochemical, and morphological properties of PBDTBD terpolymers were successfully controlled by modulating the molar ratio of DTffBT and BDD. Moreover, a PBDTBD-50:IT-4F blended film showed homogeneous film with a favorable face-on orientation. The PBDTBD-50:IT-4F blended film showed excellent hole and electron mobility, which resulted in a superior carrier balance. PBDTBD-50-based PSCs, processed with o-xylene, achieved the highest PCE of 10.03%, which is four times higher than those of copolymer-based PSCs. The novel terpolymers composed of one electron donor unit and two electron acceptor units are expected to make a considerable contribution to the development of high-performance PSCs.

Design, Synthesis and Properties of Novel BODIPY Dyes With Styryl as π‐Bridge at 3,5‐Positions

AbstractThree novel D−A‐D type small molecules Boron Fluoride Complexed Dipyridylmethine (BODIPY), BDP1‐3, linked through styryl with various strong electron donor units, such as carbazole, phenothiazine, fluorene, were designed and synthesized. The results suggest that the donor have significant effect on their photophysical and electrochemical properties. All these BDP1‐3 exhibit the obvious broader and red‐shifted absorption, the molecular absorption spectrum to range of 300–700 nm and the high molar extinction coefficients. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMU) energy level of them are calculated to be −5.18 eV and −3.21 eV, respectively. The broad and intense absorption, suitable HOMO‐LUMO energy levels make BDP1‐3 potential candidates for light‐harvesting and photovoltaic application.

Azatruxene-Based, Dumbbell-Shaped, Donor-π-Bridge-Donor Hole-Transporting Materials for Perovskite Solar Cells.

Three novel donor-π-bridge-donor (D-π-D) hole-transporting materials (HTMs) featuring triazatruxene electron-donating units bridged by different 3,4-ethylenedioxythiophene (EDOT) π-conjugated linkers have been synthesized, characterized, and implemented in mesoporous perovskite solar cells (PSCs). The optoelectronic properties of the new dumbbell-shaped derivatives (DTTXs) are highly influenced by the chemical structure of the EDOT-based linker. Red-shifted absorption and emission and a stronger donor ability were observed in passing from DTTX-1 to DTTX-2 due to the extended π-conjugation. DTTX-3 featured an intramolecular charge transfer between the external triazatruxene units and the azomethine-EDOT central scaffold, resulting in a more pronounced redshift. The three new derivatives have been tested in combination with the state-of-the-art triple-cation perovskite [(FAPbI3 )0.87 (MAPbBr3 )0.13 ]0.92 [CsPbI3 ]0.08 in standard mesoporous PSCs. Remarkable power conversion efficiencies of 17.48 % and 18.30 % were measured for DTTX-1 and DTTX-2, respectively, close to that measured for the benchmarking HTM spiro-OMeTAD (18.92 %), under 100 mA cm-2 AM 1.5G solar illumination. PSCs with DTTX-3 reached a PCE value of 12.68 %, which is attributed to the poorer film formation in comparison to DTTX-1 and DTTX-2. These PCE values are in perfect agreement with the conductivity and hole mobility values determined for the new compounds and spiro-OMeTAD. Steady-state photoluminescence further confirmed the potential of DTTX-1 and DTTX-2 for hole-transport applications as an alternative to spiro-OMeTAD.

Photoisomerization-coupled electron transfer.

Photochromic molecular structures constitute a unique platform for constructing molecular switches, sensors, and memory devices. One of their most promising applications is as light-switchable electron acceptor or donor units. Here, we investigate a previously unexplored process that we postulate may occur in such systems: an ultrafast electron transfer triggered by a simultaneous photoisomerization of the donor or the acceptor moiety. We propose a theoretical model for this phenomenon and, with the aid of density functional theory calculations, apply it to the case of a dihydropyrene-type photochromic molecular donor. By considering the wavepacket dynamics and the photoisomerization yield, we show that the two processes involved, electron transfer and photoisomerization, are in general inseparable and need to be treated in a unified manner. We finish by discussing how the efficiency of photoisomerization-coupled electron transfer can be controlled experimentally.

Hydroxy-benzimidazoles as blue-green emitters: Synthesis, structural and DFT studies

The new benzimidazole ligands (3a-e) were synthesized using ethyl 4-(butylamino)-3-nitrobenzoate and substituted salicylaldehyde in the presence of sodium dithionite reagent which undergoes “one-pot’’ nitro reductive cyclization. Here benzimidazole moiety acts as an electron-acceptor (A) whereas substituted 2-hydroxyphenyl moiety acts as an electron-donor (D) unit. The molecular structures were characterised by FTIR, 1H NMR, 13C NMR, single crystal XRD and MS analysis. Optoelectronic properties were determined by UV–vis, solution and solid photoluminescence, quantum yield and lifetime. The solvent-dependent absorption and emission were studied using both polar protic and polar aprotic solvents. All the derivatives exhibited ESIPT, especially compound ethyl 1-butyl-2-(3,5-dichloro-2-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylate (3e) displayed dual emission in both polar protic and polar aprotic solvents. The compound stability and electrochemical property were determined by thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) respectively. The compounds emit intense blue-green fluorescence with high to moderate quantum yield. Also, these derivatives exhibited a high Stokes shift. The computational studies like Density-Functional Theory (DFT) and Molecular Electrostatic Potential (MEP) were conducted to provide important insights into the structure-property relationships. The crystal packing is stabilized through intermolecular hydrogen bonds (C---H…O) and intermolecular interactions (π… π). The findings of results help in developing novel ligands in the field of organic optoelectronics.

Investigation on Y-shaped tri-fluoromethyl substituted quinoxalines: synthesis, optical and morphological studies

Y-shaped tri-fluoromethyl substituted quinoxaline derivatives 2,3-bis(4-methoxyphenyl)-6-(trifluoromethyl)quinoxaline (1) and 2,3-bis((E)-4-methoxystryryl)-6-(trifluoromethyl)quinoxaline (2) have been synthesized and characterized using various analytical and spectroscopic techniques (1H,13C, 19F NMR, FT-IR and HR-Mass). Optical properties such as absorption, emission, quantum yield, effect of solvent polarities and Aggregation Induced Emission (AIE) have been illustrated. The compound 1 exhibited negative solvatochromism and compound 2 positive solvatochromism which are in correlation with π* values by Kamlet and Taft. Compounds 1 and 2 showed large Stoke’s shifts attributed to more polar excited state of the compounds as compared to that of polar ground state, due to the presence of electron withdrawing trifluoromethyl group. Both the compounds displayed fluorescence in solid state and AIE state due to the restricted intramolecular rotation. The compounds 1 and 2 exhibited low quantum yields because of ICT (Intramolecular charge transfer) attributed to the presence of electron-donating methoxy phenyl unit and an electron-withdrawing quinoxaline unit. AIE exhibited by both the compounds in THF/water mixture were due to the formation of nano-aggregates, it is further characterised by DLS and determined the particle size to be 196.8 nm for compound 1 and 197.3 nm for compound 2. Compound 1 appeared as ice flakes and compound 2 as a cluster consisting of various micro crystals like projections in the images determined by scanning electron microscope (SEM).

Axially Chiral Biphenyl Compound-Based Thermally Activated Delayed Fluorescent Materials for High-Performance Circularly Polarized Organic Light-Emitting Diodes.

To boost intrinsic circularly polarized luminescence (CPL) properties of chiral emitters, an axially chiral biphenyl unit is inlaid in thermally activated delayed fluorescent (TADF) skeleton, urging the participation of chiral source in frontier molecular orbital distributions. A pair of enantiomers, (R)‐BPPOACZ and (S)‐BPPOACZ, containing the cyano as electron‐withdrawing moieties and carbazole and phenoxazine as electron‐donating units are synthesized and separated. The circularly polarized TADF enantiomers exhibit both high photoluminescence quantum yield of 86.10% and excellent CPL activities with maximum dissymmetry factor |g PL| values of almost 10−2 in solution and 1.8 × 10−2 in doped film, which are among the best values of previously reported small chiral organic materials. Moreover, the circularly polarized organic light‐emitting diodes based on the TADF enantiomers achieve the maximum external quantum efficiency of 16.6% with extremely low efficiency roll‐off. Obvious circularly polarized electroluminescence signals with |g EL| values of 4 × 10−3 are also recorded.

High efficiency ternary organic solar cells enabled by compatible dual-donor strategy with planar conjugated structures

Ternary organic solar cells (OSCs) have received extensive attention for improving the power conversion efficiency (PCE) of organic photovoltaics (OPVs). In this work, a novel donor material (ECTBD) consisting of benzodithiophene (BDT) central electron donor unit was developed and synthesized. The small molecular donor has the same central unit as PM6. The addition of ECTBD into PM6:Y6 system could improve the morphology of active blend layer. In addition, ECTBD showed good morphologically compatibility when blending with PM6:Y6 host, resulting in the improvement of fill factor and current density. As a result, the ternary devices based on PM6:ECTBD:Y6 ternary system achieved a highest PCE of 16.51% with fill factor of 76.24%, which was much higher than that of the binary devices (15.7%). Overall, this work provided an effective strategy to fabricate highly efficient ternary organic solar cells through design of the novel small molecular donor as the third component.

Zinc porphyrin-anthraquinonylimidazole supramolecular dyads

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 [Formula: see text] 10[Formula: see text]–3.9 [Formula: see text] 10[Formula: see text] M[Formula: see text]. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP[Formula: see text]-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

Rational Design of Near-Infrared Cyanine-Based Fluorescent Probes for Rapid In Vivo Sensing Cysteine.

Cysteine (Cys) is well-known to be an important biothiol and related to many diseases. However, the in situ trapping of endogenous Cys is still handicapped by a lack of straightforward methods combined with long-wavelength emission and high-performance response. In this work, we described the rational design strategy of cyanine-based near-infrared (NIR) probes for the rapid detection of mitochondrial Cys in living cells and mice. We focus on how to improve the response rate via regulating the electron density of the recognition units in probes. The obtained three probes all displayed remarkable fluorescence enhancement at 780 nm. From screening the obtained probes, it was found that the probe Cy-S-diOMe with electron-donating recognition unit displayed the fastest response rate, the lowest detection limit, and the highest signal-to-noise ratio. More importantly, Cy-S-diOMe was successfully applied to monitor Cys in tumor-bearing mice (within merely 5 min). This paradigm by modulation of the response rate in the cyanine dyes provides a promising methodology for the design of high-performance cyanine-based NIR probes.

Achieving High-Performance Photothermal and Photodynamic Effects upon Combining D-A Structure and Nonplanar Conformation.

Various organic nanoagents have been developed for photothermal therapy (PTT) and photodynamic therapy (PDT) under near-infrared (NIR) irradiation. Among them, small molecule-based nanoagents are very attractive due to their advantages of well-defined chemical structures, high purity, good reproducibility, and easy processability. However, only a few small molecule-based nanoagents have been developed for PDT under NIR irradiation. Moreover, the mechanism of PDT under NIR is still elusive. Herein, a semiconducting small molecule (BTA) with donor-acceptor-donor structure and twisted conformation is developed for PDT/PTT under NIR irradiation. A large π-conjugated electron-deficient unit is used as the core to couple with two electron-donating units, ensuring the strong absorption under 808 nm. Moreover, the donor-acceptor structures and twisted conformation can reduce the energy gap between the singlet and triplet states (∆EST ) to afford effective intersystem crossing, beneficial for reactive oxygen species generation. The mechanism is probed by experimental and theoretical evidence. Moreover, the BTA nanoparticles exhibit excellent biocompatibility and PTT/PDT in vitro performance under NIR irradiation. This provides a strategy for designing highly efficient PDT/PTT molecular materials.

Rhodanine-Bridged Core-Expanded Naphthalene Diimide Derivatives for n-Type Semiconductors

The core expansion of naphthalene diimides (NDIs) is an effective strategy to modulate frontier molecular orbital energy levels and improve device performances. Herein two new rhodanine-bridged and core-extended NDIs T1 and T2 were designed and synthesized. The rhodanine moiety could act not only as a π-spacer to enlarge the molecular conjugated system, but also as an electron-donating unit to tune the molecular energy levels. As a result, both T1 and T2 showed slightly lower lying LUMO energy levels (< − 4.2 eV) by ca. 0.1 eV and narrower optical band gaps (ca. 1.5 eV) by 0.5 eV compared to those of n-type organic semiconductor (OSC) NDI2DT-DTYM2.The solution-processed organic thin-film transistors based on T1 and T2 exhibited electron motilities in the range of 10−4–10−3 cm2 V−1 s−1, and the inverted perovskite solar cells constructed using T2 as electron transport materials provided a power conversion efficiency value of 8.82%. The results demonstrated that embedding rhodanine units in a NDI2DT-DTYM2 backbone is an effective approach to tune the energy levels and optical properties of OSCs, providing a new way to construct novel n-type OSCs with multifunctional optoelectronic applications.

Design Principles and Synergistic Effects of Chlorination on a Conjugated Backbone for Efficient Organic Photovoltaics: A Critical Review.

The pursuit of low-cost, flexible, and lightweight renewable power resources has led to outstanding advancements in organic solar cells (OSCs). Among the successful design principles developed for synthesizing efficient conjugated electron donor (ED) or acceptor (EA) units for OSCs, chlorination has recently emerged as a reliable approach, despite being neglected over the years. In fact, several recent studies have indicated that chlorination is more potent for large-scale production than the highly studied fluorination in several aspects, such as easy and low-cost synthesis of materials, lowering energy levels, easy tuning of molecular orientation, and morphology, thus realizing impressive power conversion efficiencies in OSCs up to 17%. Herein, an up-to-date summary of the current progress in photovoltaic results realized by incorporating a chlorinated ED or EA into OSCs is presented to recognize the benefits and drawbacks of this interesting substituent in photoactive materials. Furthermore, other aspects of chlorinated materials for application in all-small-molecule, semitransparent, tandem, ternary, single-component, and indoor OSCs are also presented. Consequently, a concise outlook is provided for future design and development of chlorinated ED or EA units, which will facilitate utilization of this approach to achieve the goal of low-cost and large-area OSCs.

Utilization of Multi-Heterodonors in Thermally Activated Delayed Fluorescence Molecules and Their High Performance Bluish-Green Organic Light-Emitting Diodes.

We report a series of pentacarbazolyl-benzonitrile derivatives such as 2,4,6-tri(9H-carbazol-9-yl)-3,5-bis(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)benzonitrile (mPyBN), 3,5-bis(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,4,6-tri(9H-carbazol-9-yl)benzonitrile (pCF3BN), 2,4,6-tri(9H-carbazol-9-yl)-3-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)-5-(3,6-diphenyl-9H-carbazol-9-yl)benzonitrile (PyPhBN), 3-(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,4,6-tri(9H-carbazol-9-yl)-5-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)benzonitrile (PyCF3BN), and 3-(3,6-bis(4-(trifluoromethyl)phenyl)-9H-carbazol-9-yl)-2,6-di(9H-carbazol-9-yl)-5-(3,6-di(pyridin-3-yl)-9H-carbazol-9-yl)-4-(9H-pyrido[3,4-b]indol-9-yl)benzonitrile (CbPyCF3BN) in which some of the carbazoles are substituted with modified 3,5-diphenyl carbazoles, exhibiting thermally activated delayed fluorescence (TADF) properties. These emitters comprised two, three, and four different types of donors, capable of bluish-green emission of around 480 nm with relatively high photoluminescence quantum yields over 90% in solution. Emitters, namely, PyPhBN, PyCF3BN, and CbPyCF3BN, composed of three and four different types of donors endowed a rather short delayed lifetime (τd) of 4.25, 5.01, and 3.65 μs in their film state, respectively. Bluish-green organic light-emitting diodes based on PyPhBN, PyCF3BN, and CbPyCF3BN exhibit a high external quantum efficiency of 20.6, 19.5, and 19.6%, respectively, with unsurpassed efficiency roll-off behavior. These results indicate that the TADF properties of multidonor type molecules can be manipulated by controlling the types and number of electron donor units.