Hwan‐Hee Cho

Hyperfluorescence shows great promise for the next generation of commercially feasible blue organic light-emitting diodes, for which eliminating the Dexter transfer to terminal emitter triplet states is key to efficiency and stability. Current devices rely on high-gap matrices to prevent Dexter transfer, which unfortunately leads to overly complex devices from a fabrication standpoint. Here we introduce a molecular design where ultranarrowband blue emitters are covalently encapsulated by insulat

Abstract The coupling of excitons in π-conjugated molecules to high-frequency vibrational modes, particularly carbon–carbon stretch modes (1,000–1,600 cm −1 ) has been thought to be unavoidable 1,2 . These high-frequency modes accelerate non-radiative losses and limit the performance of light-emitting diodes, fluorescent biomarkers and photovoltaic devices. Here, by combining broadband impulsive vibrational spectroscopy, first-principles modelling and synthetic chemistry, we explore exciton–vibr

The development of luminescent organic radicals has resulted in materials with excellent optical properties for near-infrared emission. Applications of light generation in this range span from bioimaging to surveillance. Although the unpaired electron arrangements of radicals enable efficient radiative transitions within the doublet-spin manifold in organic light-emitting diodes, their performance is limited by non-radiative pathways introduced in electroluminescence. Here we present a host-gues

High Resolution Image Download MS PowerPoint Slide Triphenylmethyl (trityl) radicals have shown potential for use in organic optoelectronic applications, but the design of practical trityl structures has been limited to donor/radical charge-transfer systems due to the poor luminescence of alternant symmetry hydrocarbons. Here, we circumvent the symmetry-forbidden transition of alternant hydrocarbons via excited-state symmetry breaking in a series of phenyl-substituted tris(2,4,6-trichlorophenyl)

Abstract Organic radicals have been of interest due to their potential to replace nonradical‐based organic emitters, especially for deep‐red/near‐infrared (NIR) electroluminescence (EL), based on the spin‐allowed doublet fluorescence. However, the performance of the radical‐based EL devices is limited by low carrier mobility which causes a large efficiency roll‐off at high current densities. Here, highly efficient and bright doublet EL devices are reported by combining a thermally activated dela

Abstract Organic radicals with fluorescence from doublet‐spin energy manifolds circumvent efficiency limits from singlet–triplet photophysics in organic light‐emitting diodes (OLEDs). The singly occupied molecular orbital (SOMO) in radicals enables the higher potential performance. The SOMO also presents substantially lower energy frontier orbitals compared to conventional fluorescent emitters for device operation, which can cause severe electron trapping that limits the performance of radical O

Efficient energy transfer in polymer blends, comprising a fluorene-based liquid-crystalline polymer (see Figure) and a non-liquid-crystalline photoluminescent polymer, is demonstrated. Low-threshold amplified spontaneous emission, originating from the efficient Förster-type energy transfer between the host and the guest molecules, is observed, which offers a wide range of lasing applications for these materials.

Abstract A wide‐gap host matrix is a major obstacle detrimentally influencing the performance of hyperfluorescent organic light‐emitting diodes since it substantially increases driving voltage. Moreover, these hyperfluorescent devices typically require at least three components in their emitting layer, which is unfavorable for mass production. To tackle the issue, hyperfluorescent organic light‐emitting diodes are reported based on a two‐component emissive system of carbene–metal–amide donors an

Abstract Linear gold complexes of the “carbene–metal–amide” (CMA) type are prepared with a rigid benzoguanidine amide donor and various carbene ligands. These complexes emit in the deep‐blue range at 424 and 466 nm with 100% quantum yields in all media. The deep‐blue thermally activates delayed fluorescence originates from a charge transfer state with an excited state lifetime as low as 213 ns, resulting in fast radiative rates of 4.7 × 10 6 s −1 . The high thermal and photo‐stability of these c

We report an effective solution process to fabricate planarized photonic crystal substrates to enhance the outcoupling efficiency of organic light-emitting diodes (OLEDs). The photonic crystal structure was fabricated using nanoimprint lithography using a UV-curable acrylate and was planarized by using a ZnO layer formed by the solgel process. The solgel process resulted in a smooth surface, and OLEDs have been successfully integrated on the planarized photonic crystal layer with a low leakage c

Abstract A series of carbene‐gold‐acetylide complexes [(BiCAAC)AuCC] n C 6 H 5− n ( n = 1, Au1 ; n = 2, Au2 ; n = 3, Au3 ; BiCAAC = bicyclic(alkyl)(amino)carbene) have been synthesized in high yields. Compounds Au1 – Au3 exhibit deep‐blue to blue‐green phosphorescence with good quantum yields up to 43% in all media. An increase of the (BiCAAC)Au moieties in gold complexes Au1 – Au3 increases the extinction coefficients in the UV–vis spectra and stronger oscillator strength coefficients supported

Energy-efficient and deep-blue organic light-emitting diode (OLED) with long operating stability remains a key challenge to enable a disruptive change in OLED display and lighting technology. Part of the challenge is associated with a very narrow choice of the robust host materials having over 3 eV triplet energy level to facilitate efficient deep-blue emission and deliver excellent performance in the OLED device. Here we show the molecular design of new 1,3,5-oxadiazines (NON)-host materials wi