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Dual nature of exciplexes: exciplex-forming properties of carbazole and fluorene hybrid trimers
摘要： Two exciplexes were detected for the first time for the known exciplex-forming system consisting of electron donating 1,3-bis-(N-carbazolyl)benzene and electron accepting 2,4,6-tris[3-(diphenyl-phosphinyl)phenyl]-1,3,5-triazine. Exploiting thermal treatment, sky-blue (high-energy) and orange (low-energy) exciplexes were observed for a solid-state mixture of the compounds under electrical excitation. Similarly, stable high-energy and low-energy exciplexes were observed for new exciplex-forming systems consisting of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine and one of four selected carbazole and fluorene hybrid trimers as donors. The high-energy exciplexes were observed when there was a small energy barrier between the locally excited state and the high-energy exciplex state. A large energy barrier between the locally excited state and the low-energy exciplex state was the reason that the dual nature of exciplexes was not discovered yet. Emission of both exciplexes was observed in electroluminescence spectra of exciplex-interface based devices using developed exiplex-forming systems as emitters. Observed under optical and electrical excitations, the low-energy exciplexes were separated using thermal treatment of the studied exciplex-forming systems. The exciplex-forming system consisting of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine and 3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole, which exhibits thermally activated delayed fluorescence, showed the best performance in organic light-emitting diodes (OLEDs) based on interface and volume exciplex emitters. The best device showed maximum external quantum and maximum current efficiencies of 18% and 54 cd A?1 respectively. Additionally, white OLEDs were fabricated exploiting sky-blue and orange emissions from a single exciplex-forming system. Our findings provide evidence of the dual nature of exciplexes and pave the way towards design of new exciplex-forming systems with high photoluminescence quantum yields and efficient exciplex-based devices.
关键词： OLEDs,fluorene,exciplexes,hybrid trimers,thermally activated delayed fluorescence,carbazole
更新于2025-09-19 17:15:36
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Exciplexa??Based Organic Lighta??Emitting Diodes with Neara??Infrared Emission
摘要： Near-infrared exciplex can weaken molecular design difficulties, and has the advantage of easy bathochromic-shift spectra via selecting the suitable electron donors and acceptors. In this contribution, exciplex is applied to fabricate near-infrared (NIR) organic light-emitting diodes (OLEDs) incorporating a synthesized fluorescent material 3-([1,1″:3′,1″-terphenyl]-5′-yl)acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (APDC-tPh) and a commercially available material 4,4′,4″-tris(carbazol-9-yl)triphenylamine (TCTA). The device having a mixed TCTA:APDC-tPh as an emitting layer shows a 730 nm NIR emission with a maximum external quantum efficiency (EQE) of about 0.1%, while the device having 2-[4-(diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA):APDC-tPh as the emitting layer exhibits an emission peak of 704 nm with a maximum EQE of 1.27%. These results prove the feasibility of fabricating the efficient exciplex-based NIR OLEDs.
关键词： donors and acceptors,near-infrared OLEDs,exciplexes,bathochromic shifts
更新于2025-09-19 17:13:59
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Recent progress on exciplex-emitting OLEDs
摘要： The thermally-activated-delayed-fluorescence (TADF) characteristics makes exciplexes being the hot subject in the organic light-emitting diode (OLED) research field. The theoretical limit for the efficiency of the conventional fluorescent OLEDs have been leaped by exploiting the triplet harvesting ability of exciplexes. Exciplexes are easily formed by blending electron donor molecules and electron acceptor molecules, which are generally hole transporting materials and electron transporting materials, respectively, resulting in easy access for employing exciplexes to OLEDs. We introduce the photo-physical characteristics of exciplexes derived from the charge-transfer characteristics and their application to OLEDs as emitters. Single exciplex-emitting OLEDs as well as exciplex emission-based white OLEDs are covered in this review.
关键词： organic light-emitting diodes,Exciplexes,thermally activated delayed fluorescence
更新于2025-09-11 14:15:04
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Rational Tuning of Molecular Interaction and Energy Level Alignment Enables High‐Performance Organic Photovoltaics
摘要： Experimental studies to reveal the cooperative relationship between spin, energy, and polarization through intermolecular charge-transfer dipoles to harvest nonradiative triplets into radiative singlets in exciplex light-emitting diodes are reported. Magneto-photoluminescence studies reveal that the triplet-to-singlet conversion in exciplexes involves an artificially generated spin-orbital coupling (SOC). The photoinduced electron parametric resonance measurements indicate that the intermolecular charge-transfer occurs with forming electric dipoles (D+?→A??), providing the ionic polarization to generate SOC in exciplexes. By having different singlet-triplet energy differences (ΔEST) in 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole (BCzPh):3′,3′″,3′″″-(1,3,5-triazine-2,4,6-triyl) tris(([1,1′-biphenyl]-3-carbonitrile)) (CN-T2T) (ΔEST = 30 meV) and BCzPh:bis-4,6-(3,5-di-3-pyridylphenyl)-2-methyl-pyrimidine (B3PYMPM) (ΔEST = 130 meV) exciplexes, the SOC generated by the intermolecular charge-transfer states shows large and small values (reflected by different internal magnetic parameters: 274 vs 17 mT) with high and low external quantum efficiency maximum, EQEmax (21.05% vs 4.89%), respectively. To further explore the cooperative relationship of spin, energy, and polarization parameters, different photoluminescence wavelengths are selected to concurrently change SOC, ΔEST, and polarization while monitoring delayed fluorescence. When the electron clouds become more deformed at a longer emitting wavelength due to reduced dipole (D+?→A??) size, enhanced SOC, increased orbital polarization, and decreased ΔEST can simultaneously occur to cooperatively operate the triplet-to-singlet conversion.
关键词： charge-transfer states,delayed fluorescence,spin–orbital coupling,orbital polarization,exciplexes
更新于2025-09-11 14:15:04