ESR and Phosphorescence Spectra of the Triplet States of Phenyl <i>s</i>-Triazines and Phenyl Benzenes

Brinen, J. S.; Koren, J. G.; Hodgson, William G.

doi:10.1063/1.1727185

Cited by 26 publications

(5 citation statements)

References 19 publications

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“…The vibrational structure in the phosphorescence of pCTRZ and mCTRZ resembles neither that observed in carbazole nor that of triazine. Rather, it closely resembles the structure obtained for carbazole-biphenyl derivatives, where the triplet state was found to be localized on the central two phenyl rings (Brinen et al, 1966 ; Bagnich et al, 2015a , b ). Thus, we conclude that the triplet state is dominated by the transition localized on the phenyl bridge and the triazine core, again in very good agreement with the theoretical predictions.…”

Section: Spectroscopic Analysissupporting

confidence: 80%

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

et al. 2020

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The synthesis of stable blue TADF emitters and the corresponding matrix materials is one of the biggest challenges in the development of novel OLED materials. We present six bipolar host materials based on triazine as an acceptor and two types of donors, namely, carbazole, and acridine. Using a tool box approach, the chemical structure of the materials is changed in a systematic way. Both the carbazole and acridine donor are connected to the triazine acceptor via a para-or a meta-linked phenyl ring or are linked directly to each other. The photophysics of the materials has been investigated in detail by absorption-, fluorescence-, and phosphorescence spectroscopy in solution. In addition, a number of DFT calculations have been made which result in a deeper understanding of the photophysics. The presence of a phenyl bridge between donor and acceptor cores leads to a considerable decrease of the triplet energy due to extension of the overlap electron and hole orbitals over the triazine-phenyl core of the molecule. This decrease is more pronounced for the para-phenylene than for the meta-phenylene linker. Only direct connection of the donor group to the triazine core provides a high energy of the triplet state of 2.97 eV for the carbazole derivative CTRZ and 3.07 eV for the acridine ATRZ. This is a major requirement for the use of the materials as a host for blue TADF emitters.

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Section: Spectroscopic Analysissupporting

confidence: 80%

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

et al. 2020

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“…In contrast, there are no significant differences between HPTs and MPTs as far as phosphorescence lifetimes and triplet energies are concerned. According to Stueber et al. , this can be explained by the assumption that the phosphorescence originates from a triplet state of the photoexcited triphenyltriazine core (see refs and for triphenyltriazine phosphorescence spectra). An extension of the mesomeric system should then lead to a bathochromic shift of the phosphorescence maximum as is actually observed for the biphenyl derivative H-OH-B (Table ).…”

Section: Resultsmentioning

confidence: 99%

Light-Induced Opening of the Intramolecular Hydrogen Bond of UV Absorbers of the 2-(2-Hydroxyphenyl)-1,3,5-triazine and the 2-(2-Hydroxyphenyl)benzotriazole Type

et al. 2000

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A number of 2-(2-hydroxyphenyl)-4,6-diaryl-1,3,5-triazines (HPTs) and TIN P (2-(2-hydroxy-5-methylphenyl)benzotriazole) show phosphorescence in polar solvents at 77 K which increases in intensity with UV-irradiation time until an equilibrium value is reached (phosphorescence evolution). TIN P phosphoresces even at the very beginning of irradiation, in contrast to the HPTs, such as M-OH-P (2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine), which exhibit no such initial phosphorescence provided that they were not recently exposed to UV radiation. The corresponding methoxy derivatives (MPTs) of some HPTs, where the H atom of the intramolecular hydrogen bond (IMHB) is replaced by a methyl group, produce intense phosphorescence independent of irradiation time. Considerable relaxation is found for HPTs after dark periods ≤ 1 h at 77 K resulting in a significantly lower initial phosphorescence intensity upon renewed irradiation. TIN P, in contrast, shows much slower relaxation which becomes significant only at elevated temperatures. Phosphorescence evolution is due to open conformers of the molecules, i.e., with intermolecular rather than intramolecular hydrogen bonds, which are formed in polar solvents under the influence of UV radiation. Relaxation, i.e., re-formation of the IMHB of open-form molecules, is faster for the investigated HPTs than for TIN P.

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“…Figure 3 shows the decrease in the zero-field splitting |D|, with increasing EQE for the TADF molecules. The |D| values for 4Cz-IPN and PXZ-TRZ are significantly smaller than those for the lowest 3 ππ* states for the unit molecules in the TADF compounds, such as carbazole (|D| = 0.1022 cm −1 ), 16 11,12diphenyl-11H,12H-indolo[2,3-a]carbazole (|D| = 0.088 cm −1 , see Figure S4, Supporting Information), triphenyl-s-triazine (|D| = 0.124 cm −1 ), 17 phenoxazine (|D| = 0.1247 cm −1 ), 18 and cyanobenzene (|D| = 0.1371 cm −1 ), 19,20 whereas Cz-T and PIC-TRZ, respectively, have |D| values close to that of carbazole and indolocarbazole rather than s-triazine. Comparison of the zero field splitting parameter indicates that the T 1 states of Cz-T and PIC-TRZ have an electronic structure of 3 ππ* localized in the carbazole part ( lo T 1 ).…”

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confidence: 91%

Mechanism of Intersystem Crossing of Thermally Activated Delayed Fluorescence Molecules

Wakikawa²,

2015

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The spin sublevel dynamics of the excited triplet state in thermally activated delayed fluorescence (TADF) molecules have not been investigated for high-intensity organic light-emitting diode materials. Understanding the mechanism for intersystem crossing (ISC) is thus important for designing novel TADF materials. We report the first study on the ISC dynamics of the lowest excited triplet state from the lowest excited singlet state with charge-transfer (CT) character of TADF molecules with different external quantum efficiencies (EQEs) using time-resolved electron paramagnetic resonance methods. Analysis of the observed spin polarization indicates a strong correlation of the EQE with the population rate due to ISC induced by hyperfine coupling with the magnetic nuclei. It is concluded that molecules with high EQE have an extremely small energy gap between the (1)CT and (3)CT states, which allows an additional ISC channel due to the hyperfine interactions.

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ESR and Phosphorescence Spectra of the Triplet States of Phenyl s-Triazines and Phenyl Benzenes

Cited by 26 publications

References 19 publications

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

High Triplet Energy Host Materials for Blue TADF OLEDs—A Tool Box Approach

Light-Induced Opening of the Intramolecular Hydrogen Bond of UV Absorbers of the 2-(2-Hydroxyphenyl)-1,3,5-triazine and the 2-(2-Hydroxyphenyl)benzotriazole Type

Mechanism of Intersystem Crossing of Thermally Activated Delayed Fluorescence Molecules

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