Herein, [Cu(P^P)(N^N)][PF6] complexes (P^P=bis[2‐(diphenylphosphino)phenyl]ether (POP) or 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos); N^N=CF3‐substituted 2,2′‐bipyridines (6,6′‐(CF3)2bpy, 6‐CF3bpy, 5,5′‐(CF3)2bpy, 4,4′‐(CF3)2bpy, 6,6′‐Me2‐4,4′‐(CF3)2bpy)) are reported. The effects of CF3 substitution on their structure as well as their electrochemical and photophysical properties are also presented. The HOMO–LUMO gap was tuned by the N^N ligand; the largest redshift in the metal‐to‐ligand charge transfer (MLCT) band was for [Cu(P^P){5,5′‐(CF3)2bpy}][PF6]. In solution, the compounds are weak yellow to red emitters. The emission properties depend on the substitution pattern, but this cannot be explained by simple electronic arguments. Among powders, [Cu(xantphos){4,4′‐(CF3)2bpy}][PF6] has the highest photoluminescence quantum yield (PLQY; 50.3 %) with an emission lifetime of 12 μs. Compared to 298 K solution behavior, excited‐state lifetimes became longer in frozen Me‐THF (77 K; THF=tetrahydrofuran), thus indicating thermally activated delayed fluorescence (TADF). Time‐dependent (TD)‐DFT calculations show that the energy gap between the lowest‐energy singlet and triplet excited states (0.12–0.20 eV) permits TADF. Light‐emitting electrochemical cells (LECs) with [Cu(POP)+(6‐CF3bpy)][PF6], [Cu(xantphos)(6‐CF3bpy)][PF6], or [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] had the fastest turn‐on time (8 min), and the LEC with the longest lifetime (t1/2=31 h) contained [Cu(xantphos)(6‐CF3bpy)][PF6]; these LECs reached maximum luminances of 131 and 109 cd m−2, respectively.
The syntheses and characterizations of six [Cu(N^N)(POP)][PF] and [Cu(N^N)(xantphos)][PF] compounds (POP = bis(2-(diphenylphosphino)phenyl)ether, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), in which N^N is a bpy ligand (1-Naphbpy, 2-Naphbpy, 1-Pyrbpy) bearing a sterically hindered 1-naphthyl, 2-naphthyl or 1-pyrenyl substituent in the 6-position, are reported. Single-crystal structure determinations of five complexes confirm a distorted tetrahedral environment for copper(i) and a preference for the N^N ligand to be oriented with the sterically-demanding aryl group being remote from the (CH)O unit of POP or the xanthene 'bowl' of xantphos. The angle between the ring planes of the bpy range from 5.8 to 26.0° and this is associated with interactions between the aryl unit and the phenyl substituents of the P^P ligand. In solution at room temperature, the complexes undergo dynamic behaviour which has been investigated using variable temperature 2D NMR spectroscopy. The [Cu(N^N)(xantphos)] complexes exist as a mixture of conformers which interconvert through inversion of the xanthene bowl-shaped unit; the preference for one conformer over the other is significantly changed on going from N^N = Phbpy to 1-Pyrbpy (Phbpy = 6-phenyl-2,2'-bipyridine). The electrochemical and photophysical properties of the [Cu(N^N)(POP)][PF] and [Cu(N^N)(xantphos)][PF] compounds are presented; the compounds are orange emitters but the introduction of the 1-naphthyl, 2-naphthyl or 1-pyrenyl substituents result in poor photoluminescence quantum yields.
A series of heteroleptic [Cu(N^N)(P^P)][PF] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λ in the range 387-395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)] to [Cu(N^N)(xantphos)]; introducing the iodo-functionality into the N^N domain leads to a red-shift in λ compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF] and [Cu(1)(xantphos)][PF] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)] and this showed a maximum luminance (Lum) of 129 cd m and a device lifetime (t) of 54 h; however, the turn-on time (time to reach Lum) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h.
The effects on photo-and electroluminescent properties of structurally modifying the bisphosphane in [Cu(N^N)(P^P)]+ complexes (N^N = bpy, 6-Mebpy, 6,6′-Me2bpy) are described.
The exploitation of a lag phase in nitrate production after anoxic periods is a promising approach to suppress nitrite oxidizing bacteria, which is crucial for implementation of the combined partial nitritation-anammox process. An in-depth study of the actual lag phase in nitrate production after short anoxic periods was performed with varied temperatures and air flow rates. In monitored batch experiments, biomass from four different full-scale partial nitritation-anammox plants was subjected to anoxic periods of 5-60 min. Ammonium and the nitrite that was produced were present to reproduce reactor conditions and enable ammonium and nitrite oxidation at the same time. The lag phase observed in nitrite oxidation exceeded the lag phase in ammonium oxidation after anoxic periods of more than 15-20 min. Lower temperatures slowed down the conversion rates but did not affect the lag phases. The operational oxygen concentration in the originating full scale plants strongly affected the length of the lag phase, which could be attributed to different species of Nitrospira spp. detected by DGGE and sequencing analysis.
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