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Elucidating the Non-Radiative Deactivation Pathways in a Cationic Iridium Complex with 2,4-di(1 <i>H</i> -pyrazol-1-yl)Pyridine as the Ancillary Ligand
摘要： Deep insight into the non-radiative deactivation pathways in phosphorescent cationic iridium complexes is critically important for developing efficient blue-emitting complexes toward advanced applications. Here, we report the synthesis, photophysical and electrochemical characterizations of a blue-green-emitting cationic iridium complex [Ir(ppy)2(bipzpy)]PF6 (Hppy is 2-phenylpyridine and bipzpy is 2,4-di(1H-pyrazol-1-yl)pyridine). The non-radiative deactivation pathways in [Ir(ppy)2(bipzpy)]PF6 have been elucidated through extensive density functional theory calculations. The calculations reveal that the higher-lying charge-transfer (CT) state in [Ir(ppy)2(bipzpy)]PF6, which arises from Ir/ppy→bipzpy transitions, favors non-radiative deactivation because of its large structural distortion compared to the ground state. Both the CT state and the dark metal-centered (3MC) state can be thermally accessed by the lowest-lying emitting triplet state at room temperature, with the former being much more easily accessible, which causes additional non-radiative deactivations for the emitting triplet state. The active roles of the CT and 3MC states in the non-radiative deactivation pathways are, for the first time, confirmed in such blue-emitting complexes with pzpy-type ancillary ligands (pzpy is 2-(1H-pyrazol-1-yl)pyridine).
关键词： charge-transfer state,metal-centered state,density functional theory,blue-emitting complexes,phosphorescent cationic iridium complexes,non-radiative deactivation
更新于2025-09-10 09:29:36
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Blue-Emitting CsPbCl <sub/>3</sub> Nanocrystals: Impact of Surface Passivation for Unprecedented Enhancement and Loss of Optical Emission
摘要： High-energy-emitting CsPbCl3 nanocrystals have shown significant loss and enhancement of their emission intensity (～40?50 folds) during purification and surface treatments, respectively. This confirms that the surfaces of these nanocrystals are very sensitive. In this Letter, physical insights of the interface bindings on the surface of these blue-emitting CsPbCl3 nanocrystals with different passivating agents and their impact on purification are investigated. Using various metal chlorides consequential irrespective of the charge and size of the metal ions, metal acetates, and nonmetal chloride, the predominant influence of chloride ions in helping retrieve/intensify the blue emission is established. The purification processes are observed to be very delicate, and successive purifications with introduction of polar nonsolvents led to the transformation of an emitting cubic CsPbCl3 phase to nonemitting tetragonal CsPb2Cl5 phase nanocrystals irreversibly. The impact of various salt additions only temporarily helped in enhancing the emission, but the phase change remained inevitable upon successive purification. However, as a remedy, by in situ use of alkylammonium chloride salt in high-temperature reactions, the surface binding was improved, and significant emission as well as the phase could be retained with successive purifications.
关键词： surface passivation,purification,optical emission,CsPbCl3 nanocrystals,blue-emitting
更新于2025-09-09 09:28:46
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Deep blue emitting Cu( <scp>i</scp> ) tripod complexes. Design of high quantum yield materials showing TADF-assisted phosphorescence
摘要： In a previous investigation, it was shown that [Cu(tpym)(PPh3)]PF6 1 with tpym = tris(2-pyridyl)methane represents a deep blue emitter (λmax = 466 nm) though with a low emission quantum yield ΦPL if doped in a polymer (7%) or dissolved in a ?uid solvent (?1%). In this study, we present new tripod compounds with [Cu(tpym)(P(o-tol)3)]PF6 2 and [Cu(tpym)(P(o-butyl-ph)3)]PF6 3 with sterically demanding ligands: P(o-tol)3 = tris(ortho-tolyl)phosphine and P(o-butyl-ph)3 = tris(ortho-n-butylphenyl)phosphine. These compounds show high emission quantum yields even in a ?uid solution (dichloromethane) reaching a benchmark value for 3 of ΦPL = 76%. This becomes possible due to the speci?c design of rigidifying the complexes. Importantly, the deep blue emission color is maintained or even further blue shifted to λmax = 452 nm (compound 3 powder). Compound 2 is characterized photophysically in detail. In particular, it is shown that the lowest excited triplet state T1 experiences very e?cient spin–orbit coupling (SOC). Accordingly, the phosphorescence decay rate is as large as 5 × 104 s?1 (20 μs) belonging to the fastest T1 → S0 transition values (shortest decay times) reported so far. Investigations down to T = 1.5 K reveal a large total zero-?eld splitting (ZFS) of 7 cm?1 (0.9 meV). Although thermally activated delayed ?uorescence (TADF) grows in at T ≥ 160 K, the phosphorescence of 2 still dominates (60%) over TADF (40%) at ambient temperature. Thus, the compound represents a singlet harvesting-plus-triplet harvesting material, if applied in an OLED.
关键词： TADF-assisted phosphorescence,Deep blue emitting,Cu(I) tripod complexes,high quantum yield
更新于2025-09-04 15:30:14