Metal‐Free OLED Triplet Emitters by Side‐Stepping Kasha’s Rule

Chaudhuri, Debangshu; Sigmund, Eva; Meyer, Annemarie; Röck, Lisa M.; Klemm, Philippe; Lautenschlager, Sebastian; Schmid, A.; Yost, Shane R.; Voorhis, Troy Van; Bange, Sebastian; Höger, Sigurd; Lupton, John M.

doi:10.1002/ange.201307601

Cited by 45 publications

(36 citation statements)

References 50 publications

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“…The LE component provides a high radiative transition rate that is related to a high photoluminescence (PL) efficiency ( η PL ), whereas the CT component is responsible for a sufficiently small singlet–triplet energy splitting (Δ E ST ), as a result of the nearly disappeared electron exchange interaction with an increased spatial separation between electron and hole wavefunctions in CT‐like excitons, which enables a high η s arising from the enhanced RISC (T→S) process along high‐lying excited states. [7b],[7e], Therefore, in principle, such excited state property could harvest the maximized EL efficiency from a compatible coexistence between high η PL and high η s , corresponding to a golden combination between LE component and CT component. What is more, the T 1 concentration quenching problem could be hopefully suppressed to a lower degree due to the restricted delayed fluorescence, if the triplet CT states were located on the high‐lying triplet energy levels, which is of shorter lifetimes than the T 1 state.…”

Section: Introductionmentioning

confidence: 99%

Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi‐Equivalent Hybridized Excited State

Zhang

Yao

Peng

et al. 2015

Adv Funct Materials

408

222

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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.

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Section: Introductionmentioning

confidence: 99%

Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi‐Equivalent Hybridized Excited State

Zhang

Yao

Peng

et al. 2015

Adv Funct Materials

408

222

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“…11,12 Both mechanisms constitute a loss of excitation energy and are ideally avoided in functional devices. 13,14 While exciton self-trapping (2) can occur on timescales of <100 fs, 5,15,16 processes (3) and (4) are generally two to three orders of magnitude slower (Figure 1b). 10,12,17,18 The similarity of characteristic timescales makes it challenging to distinguish between the competing processes of energy transfer and torsional relaxation solely on the basis of time-resolved spectroscopies.…”

Section: Introductionmentioning

confidence: 99%

Exciton Localization in Extended π-Electron Systems: Comparison of Linear and Cyclic Structures

et al. 2015

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We employ five π-conjugated model materials of different molecular shape-oligomers and cyclic structures-to investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red shift within ∼100 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while, in the macrocycle, the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the π-conjugated system in terms of disorder parameters.

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“…Namely, CZBP crystals enjoy simultaneous prompt fluorescence, DF, and RTP. Such dual emission from both singlet and triplet manifolds enables the possibility to quantify singlet–triplet spin correlations . Moreover, unlike strictly fluorescent and purely phosphorescent molecules, such efficient, simultaneous, and intrinsic fluorescence and phosphorescence (without heavy or metal atoms) in a single pure organic compound at ambient conditions is unusual and remains virtually unexplored,[7a,b] which is crucial to reveal the underlying spin correlations of organic molecules and creates new opportunities for use as optical sensors and attenuators.…”

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confidence: 99%

Achieving Persistent Room Temperature Phosphorescence and Remarkable Mechanochromism from Pure Organic Luminogens

et al. 2015

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Persistent room temperature phosphorescence (RTP) from pure organic luminogens can be rationally realized based on the crystallization-induced phosphorescence phenomenon and severe crystallization. A perfect crystal with dense molecular packing and effective inter-molecular interactions isolates the triplet excitons from quenching sites and significantly blocks the high-energy vibrational dissipation, thus yielding long-lasting RTP.

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Metal‐Free OLED Triplet Emitters by Side‐Stepping Kasha’s Rule

Cited by 45 publications

References 50 publications

Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi‐Equivalent Hybridized Excited State

Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi‐Equivalent Hybridized Excited State

Exciton Localization in Extended π-Electron Systems: Comparison of Linear and Cyclic Structures

Achieving Persistent Room Temperature Phosphorescence and Remarkable Mechanochromism from Pure Organic Luminogens

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