Thermally Activated and Aggregation‐Regulated Excitonic Coupling Enable Emissive High‐Lying Triplet Excitons**

Wang, Tao; De, Joydip; Wu, Sen; Gupta, Abhishek Kumar; Zysman‐Colman, Eli

doi:10.1002/anie.202206681

Cited by 40 publications

(43 citation statements)

References 83 publications

(5 reference statements)

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“…The lowtemperature multiple phosphorescence bands may result from restricted molecular conformations that lead to weak electronic coupling at low temperature. 20,57 We then investigated the single-crystal structures of Cz-C- 7b), which is consistent with the orange RTP of Cz-CO-PTZSO 2 originating from Cz-CO-PTZSO 2 aggregates, in addition to the green RTP from the Cz-BP moiety. For Cz-C-TRZ, π•••π intermolecular interactions exist between adjacent TRZ fragments (Figure 7c), which result in excitonic splitting and thus a lower T 1 energy (orange RTP).…”

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confidence: 52%

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Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Wang

Gupta

et al. 2023

J. Am. Chem. Soc.

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The design and regulation of multiple roomtemperature phosphorescence (RTP) processes are formidably challenging due to the restrictions imposed by Kasha's rule. Here, we report a general design principle for materials that show multiple RTP processes, which is informed by our study of four compounds where there is modulation of the linker hybridization between donor (D) and acceptor (A) groups. Theoretical modeling and photophysical experiments demonstrate that multiple RTP processes can be achieved in sp 3 C-linked D−A compounds due to the arrest of intramolecular electronic communication between two triplet states (T 1 H and T 1 L ) localized on the donor and acceptor or between two triplet states, one localized on the donor and one delocalized across aggregated acceptors. However, for the sp 2 C-linked D−A counterparts, RTP from one locally excited T 1 state is observed because of enhanced excitonic coupling between the two triplet states of molecular subunits. Single-crystal and reduced density gradient analyses reveal the influence of molecular packing on the coincident phosphorescence processes and the origin of the observed aggregate phosphorescence. These findings provide insights into higher-lying triplet excitedstate dynamics and into a fundamental design principle for designing compounds that show multiple RTP.

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confidence: 52%

“…11,49 Recently, T 1 conformer-regulated multiple phosphorescence has been demonstrated by us, which renders the excited-state dynamics tunable via thermal activation. 20,50 However, a general principle to regulate multiple phosphorescence on demand remains elusive.…”

Section: ■ Introductionmentioning

confidence: 99%

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Wang

Gupta

et al. 2023

J. Am. Chem. Soc.

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“…[ 40 ] The mCP matrix can also contribute to the suppression of non‐radiative processes in the emitters, and host–guest interactions can also regulate triplet vibronic coupling and energies. [ 30,41 ] We first studied the steady‐state PL behavior of the two emitters in mCP at various doping concentrations (Figure S20, Supporting Information). As the doping concentration increases from 1 to 10 wt%, there is only an ≈8 nm red‐shift of the PL in both of PhCz‐O‐DiKTa and PhCz‐DiKTa .…”

Section: Resultsmentioning

confidence: 99%

Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T₂State

Wang

Gupta

Cordes

et al. 2023

Advanced Optical Materials

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success of these applications. Fluorescent OLEDs can only convert 25% of singlet excitons into emission, with the loss of 75% triplet excitons as heat. [2] In the past decade, thermally activated delayed fluorescence (TADF) materials have emerged as emitters for the third-generation OLED, able to harvest 100% of excitons to generate light, at comparable exciton utilization efficiencies to phosphorescent OLEDs. Generally, TADF emitters are based on a strongly twisted donor-acceptor (D-A) design motif to electronically separate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) that results in a small energy gap between S 1 and T 1 states (ΔE S1T1 ). [3][4][5] However, a relatively large nuclear reorganization and charge-transfer (CT) transition in the excited state unavoidably produces a broad emission band, reflected by a large full width at half maximum (FWHM) of around 100 nm. [6] These undesired properties in D-A TADF emitters restrict their practical application in high-resolution displays where the color point requirements demanded by industry are difficult to obtain using materials showing broad emission.At present, commercialized high-resolution OLED displays mainly employ a color filter or microcavity to reach the color purity required by broadcasting standards, which is inevitably accompanied by losses in device efficiency and energy utilization. [7] Therefore, it would be of great utility to devise an emitter showing narrowband emission. Recently, Hatakeyama et al. introduced a subclass of TADF emitters coined multi-resonant TADF (MR-TADF), that shows the desired narrowband emission. This is due to their rigid polyaromatic hydrocarbon (PAH) framework, [8] where the rigid molecular skeleton and the shortrange CT (SRCT) nature of the emissive singlet excited state enable simultaneously narrowband emission and small ΔE S1T1 . In this design, the electron densities of the HOMO and LUMO are localized on the adjacent atoms. Typically, boron/nitrogen (B/N) doped PAHs have emerged as the dominant design. For example, Hatakeyama and co-workers designed a B/N-doped MR-TADF compound, ν-DABNA, that shows very narrowband emission (FWHM of 18 nm) at a photoluminescence (PL) maximum (λ PL ) of 467 nm, with a PL quantum yield (Φ PL ) of 90%, and where the device's maximum external quantum efficiency The S 1 state and high-lying triplet excited states (ΔE S1Tn ) offer insight into clarifying the mechanism of efficiency roll-off of organic light-emitting diodes (OLEDs). However, experimental detection of the ΔE S1Tn is challenging due to Kasha's rule. Here, two emitters, PhCz-O-DiKTa and PhCz-DiKTa, showing multi-resonant thermally activated delayed fluorescence (MR-TADF) are reported. By modulating the conjugation between the MR-TADF DiKTa emissive center and donor substituent, emission directly from the T 2 state is for the first time observed in MR-TADF emitters. Single crystal and reduced density gradient analyses reveal the origin of the reduced observed concentrationquenchi...

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“…7 Very recently, an interesting temperature-dependent dual phosphorescence emission due to thermally activated excitonic coupling between conformers having different dihedral angles was also reported. 8 However, emissions from higher triplet excited states are still scarce and the mechanism for inducing T 2 phosphorescence is not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Polarity-induced dual room-temperature phosphorescence involving the T₂ states of pure organic phosphors

et al. 2022

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Thermally Activated and Aggregation‐Regulated Excitonic Coupling Enable Emissive High‐Lying Triplet Excitons**

Cited by 40 publications

References 83 publications

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T₂State

Polarity-induced dual room-temperature phosphorescence involving the T₂ states of pure organic phosphors

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Thermally Activated and Aggregation‐Regulated Excitonic Coupling Enable Emissive High‐Lying Triplet Excitons**

Cited by 40 publications

References 83 publications

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T2State

Polarity-induced dual room-temperature phosphorescence involving the T2 states of pure organic phosphors

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Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T₂State

Polarity-induced dual room-temperature phosphorescence involving the T₂ states of pure organic phosphors