Use of Pyrimidine and Pyrazine Bridges as a Design Strategy To Improve the Performance of Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes

Santos, Paloma L. dos; Chen, Dongyang; Rajamalli, Pachaiyappan; Matulaitis, Tomas; Cordes, David B.; Slawin, Alexandra M. Z.; Jacquemin, Denis; Zysman‐Colman, Eli; Samuel, Ifor D. W.

doi:10.1021/acsami.9b16952

Cited by 75 publications

(59 citation statements)

References 34 publications

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“…We first studied the electrochemical properties of ICzTRZ in degassed DCM with tetra‐ n ‐butylammonium hexafluorophosphate as the electrolyte and Fc/Fc + as the internal reference ( Figure a). Unlike what is typically observed for carbazole‐based oxidations, which are known to be irreversible, [ 21,29–32 ] we observed a reversible oxidation wave with E ox at 0.96 V measured from the DPV. By contrast, the reduction wave at −1.83 V is irreversible.…”

Section: Resultscontrasting

confidence: 68%

Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Zhang

Crovini

Santos

et al. 2020

Advanced Optical Materials

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employing a purely organic TADF emitter, 4CzIPN. [3] TADF molecules have an energy gap between the S 1 and T 1 states, ΔE ST , sufficiently small to allow the triplet excitons to convert into singlet excitons through reverse intersystem crossing (RISC), making possible their radiative decay from the singlet excited state, evidenced by a delayed fluorescence. To minimize ΔE ST and enhance k RISC , the overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the molecule must likewise be small, which is achievable in compounds containing electron-donating and electron-accepting moieties that are poorly electronically coupled giving the excited state an intra-molecular charge-transfer (CT) character. [4] The most common emitter designs rely on a large twist angle between the donor and acceptor coupled with the incorporation of aromatic spacer bridging moieties. [5] The external quantum efficiency (EQE) of the OLED is a function not only of the IQE but also of the light out-coupling efficiency. As the stack of an OLED device is composed of several different layers of materials included between two electrodes, total internal reflection at the interface between two media, and coupling to surface plasmon polaritons (SPP) at the interface with Organic thermally activated delayed fluorescent (TADF) materials can harvest 100% of the electrically generated excitons as a result of their small singlet-triplet energy difference. However, maximizing the external quantum efficiency (EQE) of a device also requires enhancing the light out-coupling efficiency. This work presents a new acceptor-donor-acceptor (ADA) emitter employing an indolocarbazole donor and diphenyltriazine acceptors that show nearly-completely horizontal orientation regardless of the host matrix, leading to a sky-blue organic light-emitting diode (λ EL = 483 nm, CIE coordinates of 0.17, 0.32) with EQE MAX of 22.1%, a maximum luminance of 7800 cd m −2 , and blue emission.

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Section: Resultscontrasting

confidence: 68%

Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Zhang

Crovini

Santos

et al. 2020

Advanced Optical Materials

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“…The DFT modeling predicts a rather flat conformation with average dihedral angles between the 8) o ], where the pyrazine ring was similarly connected to carbazole, indicating a likely intramolecular hydrogen bonding, analogously to that observed by us for related dipyrazinylsulfone TADF emitters. [14] In both emitters, the HOMOs are distributed across the entire molecule while the LUMOs are mainly localized on the acceptor cores. [20,21] We calculated the |VSOC| 2 values as the average spin-orbital coupling matrix elements (SOCME) between their S1/T1 states and S1/T2 states based on their optimized excited-state structures, [22] which are shown in S5-S6).…”

Section: Theoretical Calculationsmentioning

confidence: 99%

“…The related N-heterocycle, pyrazine, has thus far not been explored for blue TADF emitter design, though the pyrazine has been used within an electron-acceptor design to tune its electron affinity and the corresponding energies of the emitters. [14][15][16] Recently, Duan et al reported a series of blue TADF emitters bearing pyrazine as an acceptor and benzofuro-carbazoles or benzothieno-carbazoles as donor moieties. [17] Amongst the molecules in the study, BFCZPZ2 possessed a moderately small ΔEST (0.31 eV in PPT) and high photoluminescence quantum yield (PLQY) (91% in PPT).…”

Section: Introductionmentioning

confidence: 99%

Planar and Rigid Pyrazine Based TADF Emitter for Deep Blue Bright Organic Light Emitting Diodes

Rajamalli¹,

Chen²,

Suresh³

et al. 2021

Preprint

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Two blue thermally activated delayed fluorescence (TADF) emitters bearing di-tert-butyl carbazoles as the electron donor groups and pyrazine (DTCz-Pz) or dipyrazine (DTCz-Pz) as the electron acceptor are presented. The DFT calculations predict DTCz-Pz and DTCz-DPz to possess high S1 energies (3.19 eV and 3.08 eV, respectively), and relatively large EST values (0.52 eV and 0.56 eV, respectively). The closely layered intermediate triplet states between S1 and T1, predicted by DFT calculations, are expected to facilitate the reverse intersystem crossing (RISC) and improve spin-vibronic coupling efficiency between the excited states even the relatively larger ΔESTs. The ΔESTs for DTCz-Pz and DTCz-DPz are 0.27 eV and 0.38 eV, and both molecules show high photoluminescence quantum yields (65%, and 70%, respectively) and the decay lifetimes show temperature dependence in a PPT host, which is consistent that both molecules are TADF emitters in PPT. The OLEDs based on DTCz-Pz exhibit deep blue emission with λEL of 460 nm and CIE of (0.15, 0.16). The maximum external quantum efficiency (EQEmax) reaches 11.6%, with a maximum luminance (Lmax) of up to 6892 cd m-2, while the device based on DTCz-DPz exhibits sky blue emission with λEL of 484 nm and CIE of (0.15, 0.30), an EQEmax of 7.2%, and Lmax of 8802 cd m-2.

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“…This is due to their ability to utilize both singlet excitons and triplet excitons, thereby increasing the theoretical internal quantum efficiency (IQE) to 100% from 25% for fluorescent compounds [1][2][3][4]. For TADF materials, a small energy gap between the lowest singlet and triplet excited states (ΔE ST ) is essential to permit the efficient up-conversion of triplet excitons to singlet excitons via reverse intersystem crossing (rISC) [5][6][7]. The rISC process can happen by hyperfine coupling when the ΔE ST is sufficiently small (<10 meV) or spin orbit coupling (SOC), which requires different symmetry between the two states coupled with a relatively small singlet-triplet energy gap, ΔE ST , (<300 meV) [8,9].…”

Section: Introductionmentioning

confidence: 99%

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

Chen¹,

Zysman‐Colman²

2021

Beilstein J. Org. Chem.

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The trifluoromethyl group has been previously explored as a non-conjugated electron-withdrawing group in donor–acceptor thermally activated delayed fluorescence (TADF) emitters. In the present study, we investigate computationally the potential of other fluorine-containing acceptors, trifluoromethoxy (OCF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5), within two families of donor–acceptor TADF emitters. Time-dependent density functional theory calculations indicate that when only two ortho-disposed carbazole donors are used (Type I molecules), the lowest-lying triplet state possesses locally excited (LE) character while the lowest-lying singlet state possesses charge-transfer character. When five carbazole donors are present in the emitter design (Type II molecules), now both S1 and T1 states possess CT character. For molecules 2CzOCF 3 and 5CzOCF 3 , the singlet energies are predicted to be 3.92 eV and 3.45 eV; however, the singlet-triplet energy gaps, ΔE STs, are predicted to be large at 0.46 eV and 0.37 eV, respectively. The compounds 2CzCF 3 , 2CzSCF 3 , and 2CzSF 5 , from Type I molecules, show significant promise as deep blue TADF emitters, possessing high calculated singlet energies in the gas phase (3.62 eV, 3.66 eV, and 3.51 eV, respectively) and small, ΔE STs, of 0.17 eV, 0.22 eV, and 0.07 eV, respectively. For compounds 5CzSCF 3 and 5CzSF 5 , from Type II molecules, the singlet energies are stabilized to 3.24 eV and 3.00 eV, respectively, while ΔE STs are 0.27 eV and 0.12 eV, respectively, thus both show promise as blue or sky-blue TADF emitters. All these six molecules possess a dense number of intermediate excited states between S1 and T1, thus likely leading to a very efficient reverse intersystem crossing in these compounds.

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Use of Pyrimidine and Pyrazine Bridges as a Design Strategy To Improve the Performance of Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes

Cited by 75 publications

References 34 publications

Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Efficient Sky‐Blue Organic Light‐Emitting Diodes Using a Highly Horizontally Oriented Thermally Activated Delayed Fluorescence Emitter

Planar and Rigid Pyrazine Based TADF Emitter for Deep Blue Bright Organic Light Emitting Diodes

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

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