Two new red-emitting ternary europium(III) complexes with high photoluminescence quantum yields and exceptional performance in OLED devices.

Two new organo-europium complexes (OEuCs) [Eu(btfa)3(Bathphen)] (OEuC-1) and [Eu(tta)3(Bathphen)] (OEuC-2) where btfa and tta are the anions of 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 2-thenoyltrifluoroacetone while Bathphen = Bathophenanthroline have been synthesized and characterized. Both complexes in the solid state exhibit strong red emissions with photoluminescence quantum yields (PLQYs) of 80% ± 10%. These complexes were tested as dopants in the emitting layer (EML) to fabricate red organic light emitting diodes (R-OLEDs). Through device engineering involving the amalgamation of appropriate host materials and complexes, we have achieved exceptional overall R-OLED performance for an OEuC-2 based device, with maximum current efficiency (CEmax) = 9.91 cd A-1, maximum power efficiency (PEmax) = 9.15 lm W-1, maximum external quantum efficiency (EQEmax.) = 6.24%, brightness (B) of 545 cd m-2, and (CIE)x,y = 0.620, 0.323 at J = 10 mA cm-2.

Single component white-OLEDs derived from tris(ß-diketonato) europium(III) complexes bearing the large bite angle N

Two new organo-europium complexes (OEuCs) [Eu(tfac)3(TB-Im)] (Eu1) [Eu(hfac)3(TB-Im)] (Eu2) incorporating fluorinated (hexafluoroacetylacetone; Hhfaa) or hemi-fluorinated (trifluoroacetylacetone; Htfac) ß-diketones together with the large bite angle N^N ligand (2-(4-thiazolyl)benzimidazole; TB-Im) have been synthesized and characterized. The structure of the complexes has been established by single crystal X-ray diffraction (SC-XRD) analysis and shows that the coordination sphere is composed of a EuO6N2 core (octacoordinated). Continuous shape measures (CShMs) revealed that the geometry around Eu(III) is trigonal dodecahedral with approximate D2d-symmetry. Efficient red emission is observed for both the complexes in solution with a fairly large photoluminescence quantum yield (PLQY (QLEu) = 39.00-47.00%). Furthermore, by utilizing the experimental photoluminescence (PL) data and theoretical modelling employing density functional theory (DFT) in conjunction with LUMPAC, energy transfer (ET) and back energy transfer rates were calculated, and an ET mechanism for the sensitized PL is proposed and discussed in detail. Finally, the complexes were used as an emitting layer (EML) to fabricate 20 organic light emitting diodes (OLEDs) by varying the doping concentration. Interestingly, both the complex-based OLEDs at 4 wt% doping concentration display white electroluminescence (EL) with the brightness (B) = 100.5-364.1 cd m-2 at very low turn-on voltage (Vturn-on) = 3.9-4.6 V. The overall electroluminescence performance of Eu1 and Eu2 is higher than that of the reported europium based single component white-OLEDs.

Electronic and steric effects of platinum(ii) di-yne and poly-yne substituents on the photo-switching behaviour of stilbene: experimental and theoretical insights.

A series of mono-, di-, and poly(platina-ynes) incorporating stilbene spacer units with the formulae trans-[R-C[triple bond, length as m-dash]C-Pt(PBu3)2-C[triple bond, length as m-dash]C-R] (R = (E)-1,2-diphenylethene), trans-[(Ph)-(Et3P)2PtC[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]CPt(PEt3)2(Ph)] (R = (E)-1,2-diphenylethene), and trans-[-(PnBu3)2PtC[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]C-]n (R = (E)-1,2-diphenylethene), respectively, have been synthesized and characterized to explore the effects of ligand topology on the photoisomerization and photophysical properties of these materials. The structural and photophysical properties of the complexes have been investigated and compared with those of the previously reported mono-, di- and poly(platina-ynes) incorporating azobenzene spacers. We found that the organometallic species 1M, 2M and 1P undergo topology-dependent reversible trans-to-cis photoisomerization in CH2Cl2 solution. Computational modelling supported the experimental findings.

Utilization of a Pt(ii) di-yne chromophore incorporating a 2,2'-bipyridine-5,5'-diyl spacer as a chelate to synthesize a green and red emitting d-f-d heterotrinuclear complex.

A new heterotrinuclear (d-f-d) complex [Eu(btfa)31c] (btfa = 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1c = [(Ph)(Et3P)2Pt-C[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]C-Pt(Et3P)2(Ph)] (R = 2,2'-bipyridine-5,5'-diyl) has been synthesized by utilizing the N,N-donor sites of the organometallic chromophore. The complex was characterized by analytical and spectroscopic methods. Photophysical properties of the complex were analysed in detail using both steady-state and time-resolved emission and excitation spectroscopy. The optical absorption spectrum of the complex is dominated by the spin allowed π-π* transitions of the btfa and 1c units in the UV-visible region (200-418 nm) and thus is excitable over a wide range of wavelengths across the UV into the visible region of the electromagnetic spectrum. The complex displays typical red Eu(iii) emission when excited at 345 nm. However, it also shows green emission when excited at 464 nm and, thus could be an interesting candidate for full colour display applications. The change in the colour could be a result of the high value of the energy back-transfer rate (6.73 × 105 s-1) from the triplet state of the organometallic chromophore to the 5D1 state of Eu(iii). Judd-Ofelt (J-O) intensity parameters (Ω2 and Ω4), radiative (AR), non-radiative (AR) decay rates and intrinsic quantum yield (Q) have been calculated.

Correction: Utilization of a Pt(II) di-yne chromophore incorporating a 2,2'-bipyridine-5,5'-diyl spacer as a chelate to synthesize a green and red emitting d-f-d heterotrinuclear complex.

Correction for 'Utilization of a Pt(ii) di-yne chromophore incorporating a 2,2'-bipyridine-5,5'-diyl spacer as a chelate to synthesize a green and red emitting d-f-d heterotrinuclear complex' by Idris Juma Al-Busaidi et al., Dalton Trans., 2021, DOI: 10.1039/d0dt04198j.

Two Is Better than One? Investigating the Effect of Incorporating Re(CO)3Cl Side Chains into Pt(II) Diynes and Polyynes.

Pt(II) diynes and polyynes incorporating 5,5'- and 6,6'-disubstituted 2,2'-bipyridines were prepared following conventional Sonogashira and Hagihara dehydrohalogenation reaction protocols. Using Pt(II) dimers and polymers as a rigid-rod backbone, four new heterobimetallic compounds incorporating Re(CO)3Cl as a pendant functionality in the 2,2'-bipyridine core were obtained. The new heterobimetallic Pt-Re compounds were characterized by analytical and spectroscopic techniques. The solid-state structures of a Re(I)-coordinated diterminal alkynyl ligand and a representative model compound were determined by single-crystal X-ray diffraction. Detailed photophysical characterization of the heterobimetallic Pt(II) diynes and polyynes was carried out. We find that the incorporation of the Re(CO)3Cl pendant functionality in the 2,2'-bipyridine-containing main-chain Pt(II) diynes and polyynes has a synergistic effect on the optical properties, red shifting the absorption profile and introducing strong long-wavelength absorptions. The Re(I) moiety also introduces strong emission into the monomeric Pt(II) diyne compounds, whereas this is suppressed in the polyynes. The extent of the synergy depends on the topology of the ligands. Computational modeling was performed to compare the energetic stabilities of the positional isomers and to understand the microscopic nature of the major optical transitions. We find that 5,5'-disubstituted 2,2'-bipyridine systems are better candidates in terms of yield, photophysical properties, and stability than their 6,6'-substituted counterparts. Overall, this work provides an additional synthetic route to control the photophysical properties of metallaynes for a variety of optoelectronic applications.

Synthesis and crystal structure of an M4L6 tetrahedral cage with outward-facing pockets from a substituted pyrazolyl-pyridine ligand.

The self-assembly of metal-polydentate ligands to give supramolecular tetrahedral complexes is of considerable current interest. A new ligand, 4-benzyl-2-[1-(2-{[3-(4-benzylpyridin-2-yl)-1H-pyrazol-1-yl]methyl}benzyl)-1H-pyrazol-3-yl]pyridine (L), with chelating pyrazolyl-pyridine units substituted on the 4-position of the pyridyl ring with benzyl units, has been synthesized and fully characterized. The self-assembly of L with cobalt(II) gave rise to a tetrahedral cage (hexakis{µ-4-benzyl-2-[1-(2-{[3-(4-benzylpyridin-2-yl)-1H-pyrazol-1-yl]methyl}benzyl)-1H-pyrazol-3-yl]pyridine}perchloratotetracobalt(II) octakis(perchlorate) acetonitrile undecasolvate, [Co4(ClO4)(C38H32N6)6](ClO4)7·11CH3CN) with approximate T symmetry. The X-ray crystal structure of the cage, i.e. [Co4L6-ClO4](ClO4)7, shows that the substituted benzyl groups are oriented away from the centres of their respective ligands towards the CoII vertices, making small outward-facing pockets from three benzyl rings at the corners of the tetrahedron.

Mixed-ligand molecular paneling: dodecanuclear cuboctahedral coordination cages based on a combination of edge-bridging and face-capping ligands.

Reaction of a tris-bidentate ligand L(1) (which can cap one triangular face of a metal polyhedron), a bis-bidentate ligand L(2) (which can span one edge of a metal polyhedron), and a range of M(2+) ions (M = Co, Cu, Cd), which all have a preference for six coordination geometry, results in assembly of the mixed-ligand polyhedral cages [M12(mu(3)-L(1))4(mu-L(2))12](24+). When the components are combined in the correct proportions [M(2+):L(1):L(2) = 3:1:3] in MeNO2, this is the sole product. The array of 12 M(2+) cations has a cuboctahedral geometry, containing six square and eight triangular faces around a substantial central cavity; four of the eight M3 triangular faces (every alternate one) are capped by a ligand L(1), with the remaining four M3 faces having a bridging ligand L(2) along each edge in a cyclic helical array. Thus, four homochiral triangular {M3(L(2))3}(6+) helical units are connected by four additional L(1) ligands to give the mixed-ligand cuboctahedral array, a topology which could not be formed in any homoleptic complex of this type but requires the cooperation of two different types of ligand. The complex [Cd3(L(2))3(ClO4)4(MeCN)2(H2O)2](ClO4)2, a trinuclear triple helicate in which two sites at each Cd(II) are occupied by monodentate ligands (solvent or counterions), was also characterized and constitutes an incomplete fragment of the dodecanuclear cage comprising one triangular {M3(L(2))3}(6+) face which has not yet reacted with the ligands L(1). (1)H NMR and electrospray mass spectrometric studies show that the dodecanuclear cages remain intact in solution; the NMR studies show that the Cd 12 cage has four-fold (D2) symmetry, such that there are three independent Cd(II) environments, as confirmed by a (113)Cd NMR spectrum. These mixed-ligand cuboctahedral complexes reveal the potential of using combinations of face-capping and edge-bridging ligands to extend the range of accessible topologies of polyhedral coordination cages.

Enantiodifferentiation of chiral cationic cages using trapped achiral BF4- anions as chirotopic probes.

The addition of enantiopure TRISPHAT anions to chiral cationic cages of type [Co(4)(L)(6)(BF(4))](7+) leads to the enantiodifferentiation of the ligands of the racemic salts and, even more effectively, of the achiral tetrafluoroborate anion trapped inside.

Red-shifted luminescence from naphthalene-containing ligands due to pi-stacking in self-assembled coordination cages.

Incorporation of ligands containing substituted naphthalene cores into coordination cages results in extensive aromatic pi-stacking between ligands; this results in a red-shifted 'excimer-like' luminescence component from the naphthyl groups compared to the free ligands, which is diagnostic of, and can be used to monitor, cage assembly.