With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue ...neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455–485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., −F or −CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO–LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A–1, an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m–2. Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices.
Achieving a selective 2 e− or 4 e− oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We ...designed Co porphyrin 1 with meso‐phenyls each bearing a bulky ortho‐amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers αβαβ and αααα catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O2), respectively, but ααββ and αααβ show poor selectivity with n=2.89–3.10. Isomer αβαβ catalyzes 2 e− ORR by preventing a bimolecular O2 activation path, while αααα improves 4 e− ORR selectivity by improving O2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K‐edge near‐edge X‐ray absorption fine structure. This work represents an unparalleled example to improve 2 e− and 4 e− ORR by tuning only steric effects without changing molecular and electronic structures.
Cobalt porphyrin atropisomers with similar electronic structures but dissimilar steric effects were synthesized. One isomer is selective for the 2 e− ORR, one is selective for the 4 e− ORR, while the other two show poor selectivity for either 2 e− or 4 e− ORR.
The benzoyl peroxide (BPO)-promoted phenanthridinylation of simple alkanes with isonitrile is developed via C(sp(3))-H and C(sp(2))-H bond cleavage. This procedure is featured by dual C-C bond ...formation proceeding with the addition of an alkyl radical to isonitrile followed by radical aromatic cyclization.
Two inverse 2-pyridyl-1,2,3-triazole “click” ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their palladium(II), platinum(II), rhenium(I), and ...ruthenium(II) complexes have been synthesized in good to excellent yields. The properties of these inverse “click” complexes have been compared to the isomeric regular compounds using a variety of techniques. X-ray crystallographic analysis shows that the regular and inverse complexes are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine (R = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine (R = phenyl, benzyl) “click” chelators. Additionally, the bis-2,2′-bipyridine (bpy) ruthenium(II) complexes of the “click” chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole ruthenium(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium(I) and platinum(II) complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group R and triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium(I) complexes have large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are relatively solvent insensitive.
A bright combination: A new type of donor–acceptor dyad, carbazolylaryl‐substituted ortho‐carboranes, which are conveniently prepared from the corresponding acetylenes and decaborane pathways, showed ...unique excited‐state behavior associated with electron transfer unlike the meta‐ and para‐counterparts (see picture).
Stepwise locking of phenyl rings of tetraphenylethene increases the emission efficiency of luminogen solutions gradually, thus verifying the restriction of intramolecular rotation (RIR) mechanism of ...the aggregation induced emission phenomenon. The emission of the luminogen with one "O" bridge could be tuned reversibly in solid state through repeated heating and grinding.
A direct method to construct 2-oxazolines and 2-thiazolines from corresponding allylic amides and thioamides is reported. The redox-neutral intramolecular hydrofunctionalization is enabled by a dual ...catalyst system comprised of the 9-mesityl-
-methyl acridinium tetrafluoroborate and phenyl disulphide and exhibits complete selectivity for the
-Markovnikov regioisomeric products. The cyclization of allylic thioamides is postulated to operate via a modified mechanism in which oxidation of the thioamide, rather than the alkene, is responsible for the observed reactivity.
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 (C
H
)
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.
Understanding the bonding trends within, and the differences between, the 4f and 5f element series with soft donor atom ligands will aid elucidation of the fundamental origins of actinide (An)
versus
...lanthanide (Ln) selectivity that is integral to many advanced nuclear fuel cycle separation concepts. One of the principal obstacles to acquiring such knowledge is the dearth of well characterized transuranic molecules that prevents the necessary comparison of 4f
versus
5f coordination chemistry, electronic structure, and bonding. Reported herein is new chemistry of selenium analogues of dithiophosphinate actinide extractants. Ln
III
and An
III/IV
complexes with the diselenophosphinate Se
2
PPh
2
−
anion have been synthesized, structurally and spectroscopically characterized, and quantum chemical calculations performed on model compounds in which the phenyl rings have been replaced by methyl groups. The complexes Ln
III
(Se
2
PPh
2
)
3
(THF)
2
(Ln = La (
1
), Ce (
2
), Nd (
3
)), La
III
(Se
2
PPh
2
)
3
(MeCN)
2
(
4
), Pu
III
(Se
2
PPh
2
)
3
(THF)
2
(
5
), Et
4
NM
III
(Se
2
PPh
2
)
4
(M = Ce (
6
), Pu (
7
)), and An
IV
(Se
2
PPh
2
)
4
(An = U (
8
), Np (
9
)), represent the first f-element diselenophosphinates. In conjunction with the calculated models, complexes
1-9
were utilized to examine two important factors: firstly, bonding trends/differences between trivalent 4f and 5f cations of near identical ionic radii; secondly, bonding trend differences across the 5f series within the An
IV
oxidation state. Analysis of both experimental and computational data supports the conclusion of enhanced covalent bonding contributions in Pu
III
-Se
versus
Ce
III
-Se bonding, while differences between U
IV
-Se and Np
IV
-Se bonding is satisfactorily accounted for by changes in the strength of ionic interactions as a result of the increased positive charge density on Np
IV
compared to U
IV
ions. These findings improve understanding of soft donor ligand binding to the f-elements, and are of relevance to the design and manipulation of f-element extraction processes.
A series of 1 : 3 and 1 : 4 Ln(
iii
), An(
iii
) and An(
iv
) complexes with diselenophosphinate ligands have been synthesized, isolated, characterized and structurally analysed, along with computational models, to reveal new insights into f-element bonding trends and differential covalency.
Two compounds with a tri-carbazole (3Cz) structure, namely 3,6-di(carbazol-9-yl)- N -(4-nitrophenyl)carbazole (NO 2 -3Cz) and 3,6-di(carbazol-9-yl)- N -(4-aminophenyl)carbazole (NH 2 -3Cz), were ...synthesized and electropolymerized into robust polymer films on the electrode surface in an electrolyte solution via the oxidative coupling reactions. The electro-generated polymer films exhibited reversible electrochemical oxidation processes, with significant electrochromic behaviour. The colour of P(NO 2 -3Cz) films changed from the pale yellow neutral state to yellow-green as a radical cation and then to blue when fully oxidized. Upon oxidation, the colour of P(NH 2 -3Cz) films changed from colourless to pale green and finally to blue. Furthermore, we also synthesized and characterized some N -phenylcarbazoles with different substituents on the phenyl group. Based on a comparative study, the possible electropolymerization mechanisms of the NO 2 -3Cz and NH 2 -3Cz monomers are suggested; that of the former is through carbazole–carbazole coupling, and the latter is through both carbazole–carbazole and NH 2 –carbazole coupling.
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