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Effect of intermolecular interaction on excited-state properties of thermally activated delayed fluorescence molecules in solid phase: A QM/MM study
摘要： Recently, thermally activated delayed fluorescence (TADF) molecules have attracted great attention since nearly 100% exciton usage efficiency was obtained in TADF molecules. Most TADF molecules used in organic light-emitting diodes are in aggregation state, so it is necessary to make out the intermolecular interaction on their photophysical properties. In this work, the excited-state properties of the molecule AI-Cz in solid phase are theoretically studied by the combined quantum mechanics and molecular mechanics (QM/MM) method. Our results show that geometry changes between the ground state (S0) and the first singlet excited state (S1) are limited due to the intermolecular π-π and CH-π interactions. The energy gap between S1 and the first triplet excited state is broadened and the transition properties of excited states are changed. Moreover, the Huang-Rhys factors and the reorganization energy between S0 and S1 are decreased in solid phase, because the vibration modes and rotations are hindered by intermolecular interaction. The non-radiative rate has a large decrease in solid phase which improves the light-emitting performance of the molecule. Our calculation provides a reasonable explanation for experimental measurements and highlights the effect of intermolecular interaction on excited-states properties of TADF molecules.
关键词： Hybridized local and charge transfer state,Thermally activated delayed fluorescence,Intermolecular interactions,QM/MM method
更新于2025-09-23 15:21:01
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A novel hot exciton blue fluorophores and white organic light-emitting diodes with simplified configuration
摘要： The two efficient non-doped blue emitters with hybridized local and charge transfer state namely, NDBNPIN and DBTPIN have been synthesised and characterised. These materials are employed as a host for green and red phosphorescent OLEDs. The white device based on DBTPIN:Ir(MDQ)2(acac) (4%) exhibit maximum external quantum efficiency (ηex) ?24.8%; current efficiency (ηc) ?57.1 cdA?1; power efficiency (ηp) ?64.8 lmW?1 with Commission Internationale de l’Eclairage (CIE:0.49, 0.40) than NDBNPIN:Ir(MDQ)2acac (4%) device [ηex ? 23.1%; ηc ?54.6 cd A?1; ηp? 60.0 lm W?1 with CIE (0.47, 0.42)]. Development of blue emitter is crucial in organic light emitting devices (OLEDs) to reduce power consumption effectively1. For an OLED with stable emission the current efficiency (CE) is proportional to external quantum efficiency (?ex): power efficiency (PE) is determined by CE and operating voltage (V) [PE = π CE/V]2–4. Iridium and platinum based phosphorescent complexes and TADF (thermally activated delayed fluorescent materials) exhibit high ?ex, however, suffered with short lifetime and roll-off efficiency and also the production cost of phosphorescent materials are unfavourable for practical applications5. Therefore, low driving voltage with high brightness become the major issue to achieve efficient OLEDs6. In OLEDs, balanced hole: electron recombination leads to formation of CT exciton (charge-transfer) which undergo decay directly or relaxes to LE (local exciton), thus, utilization of both CT exciton and LE provides efficient EL (electroluminescence). From 4-(dicyanomethylene)-2-methyl-6-[4-(dimethylaminostyryl)-4H-pyran] with CT state maximum efficiency have been harvested7–9. Donor–acceptor (D–A) compounds with low % CT leads to RISC (reverse intersystem crossing) process which results high singlet utilisation efficiency(?s), however, colour-purity is still poor due to broadened PL (photoluminescence) and EL (electroluminescence) spectra10–13. D-A architecture with high % LE state leads to higher efficiency because of maximum orbital overlap whereas high % CT provides low efficiency due to partial hole and electron overlap. However, because of small energy splitting (ΔES-T ≈ 0) CT state undergo RISC process 11,12. These issues are overcome, by employing D–A configured emissive materials with results in enhanced ηs HLCT emissive state: stabilised LE and CT states results in ηPL(photoluminance efficiency) and high ηs.. Thus, construction of D–A emitters with HLCT emissive state is novel strategy to design efficient blue emitters.
关键词： hybridized local and charge transfer state,blue emitters,OLEDs,electroluminescence,phosphorescent
更新于2025-09-23 15:19:57