Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering.

Defect engineering has been generally observed and utilized in crystal materials including metal oxides, metal-organic frameworks, and so on; however, how to relate the defect formation and crystallization process is needed to be revealed clearly, and how to heal the defect is a big challenge. Herein, based on the new coordination complex (HNU-53), the crystal defects were created by increasing the reaction time and crystal size. Following the crystal growth process, the crystal color centers were simultaneously generated, resulting in fluorescence quenching. To heal the defect, the crystal growth was controlled by the introduction of rare earth ions. With the coordination competition of rare earth ions, the crystal defects were reduced and recovery of fluorescence emission was achieved.

Circularly polarized luminescence of pinene-modified tetradentate platinum(II) enantiomers containing fused 5/6/6 metallocycles.

In this study, a couple of tetradentate Pt(II) enantiomers ((-)-1 and (+)-1) and a couple of tetradentate Pt(IV) enantiomers ((-)-2 and (+)-2) containing fused 5/6/6 metallocycles have been synthesized by controlling reaction conditions. Two valence forms could transform into each other through mild chemical oxidants and reductants. Single-crystal X-ray diffraction confirms the structures of (-)-1 and (-)-2. The coordination sphere of the Pt(II) cation in (-)-1 displays a distorted square-planar geometry and a platinum centroid helix chirality. In contrast, the structure of (-)-2 reveals a distorted octahedral geometry. The solution and the solid of (-)-1 are highly luminescent. Complex (-)-1 shows a prominent aggregation-induced emission enhancement (AIEE) behavior in DMSO/water solution with emission quantum yield (Φ em) up to 73.2%. Furthermore, highly phosphorescent Pt(II) enantiomers exhibit significant circularly polarized luminescence (CPL) with a dissymmetry factor (g lum) of order 10-3 in CH2Cl2 solutions at room temperature. Symmetrically appreciable CPL signals are observed for the enantiomers (-)-1 and (+)-1.

The combination of skeleton-engineering and periphery-engineering: a design strategy for organic doublet emitters.

The emergence and development of radical luminescent materials is a huge breakthrough toward high-performance organic light-emitting diodes (OLEDs) without spin-statistical limits. Herein, we design a series of radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) by combining skeleton-engineering and periphery-engineering strategies, and present some insights into how different chemical modifications can modulate the chemical stability and luminescence properties of radicals by quantum chemistry methods. Firstly, through the analysis of the geometric structure changes from the lowest doublet excited state (D1) to the doublet ground state (D0) states, the emission energy differences between the BN orientation isomers are explained, and it is revealed that the radical with a smaller dihedral angle difference can more effectively suppress the geometric relaxation of the excited states and bring a higher emission energy. Meanwhile, a comparison of the excited state properties in different radicals can help us to disclose the luminescence behavior, that is, the enhanced luminescent intensity of the radical is caused by the intensity borrowing between the charge transfer (CT) state and the dark locally excited (LE) state. In addition, an efficient algorithm for calculating the internal conversion rate (kIC) is introduced and implemented, and the differences in kIC values between designed radicals are explained. More specifically, the delocalization of hole and electron wave functions can reduce nonadiabatic coupling matrix elements (NACMEs), thus hindering the non-radiative decay process. Finally, the double-regulation of chemical stability and luminescence properties was realized through the synergistic effect of skeleton-engineering and periphery-engineering, and to screen the excellent doublet emitter (BN-41-MPTTM) theoretically.

A supported Cr-Cr sextuple bond in an all-metal cluster.

Herein, we report a distinct Cr-Cr sextuple bond with an ultra-short length stabilized by equatorial alkali metals. Bonding analyses indicate that the two desired 4p-pi bonds failed to be formed but the bonding strength is enhanced due to the introduction of alkali metals, weakening the Cr-Cr 4s-4s effect. The Cr-Cr sextuple bond comprises five explicit 3d-3d overlaps and another delocalized σ bond.

Extensive generation and characterization of ion clusters by silicopolyoxometalate anions under matrix-assisted laser desorption/ionization conditions in the gas phase.

RATIONALE: The research area of ion clusters has helped to enrich the study of chemical bonding theory, clarify the crystal nucleation process and investigate the cluster ion-molecule reactions. The mass spectrometry (MS) technique, especially high-resolution MS, is an important method for investigating ion clusters in the gas phase. As polyoxometalates (POMs) have been attracting considerable interest in biochemistry, medicine and materials science due to their excellent structural and electronic features it is important to characterize these clusters by MS. METHODS: Singly negatively charged molybdenum-containing and tungsten-containing ion clusters with different matrices were produced by Keggin-type silicopolyoxometalate anions under matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS) conditions. RESULTS: The matrices displayed an obvious influence on the formation of ion clusters. It was found that the molybdenum-containing ion species [(HSiO3 )(MoO3 )n ]- , [(SiO2 )m (MoO3 )n (H2 O)x ] -• , [(OH)(MoO3 )n ]-• , [(MoO3 )n ]-• , and [Hx SiMoy Oz ]- were the main ion series in the mass spectra. For the tungsten-containing ion clusters, [(HSiO3 )(WO3 )n ]- , [(C8 H5 Om )(WO3 )n (H2 O)x ]- , [(OH)(WO3 )n ]- , and [(WO3 )n ]-• were the main ion species in the mass spectra, and a series of organic-inorganic hybrid tungsten-containing ion clusters [(C8 H5 Om )(WO3 )n (H2 O)x ]- were generated by the interaction of DHAP and THAP matrices with tungstate anions. Furthermore, the most abundant species (magic number) in each ion series indicated that they might adopt more stable structures than other relevant clusters. CONCLUSIONS: Keggin-type silicopolyoxometalate anions can produce several series of singly charged molybdenum-containing/tungsten-containing ion clusters in negative-ion generating mode under MALDI conditions. It is proposed that the "Lucky Survivors" hypothesis may be used to illustrate the generation of ion clusters in the gas phase during the early stages of plume expansion. In addition, clear evidence of hydrogen transfer and electron capture to POMs was found in the obtained MALDI mass spectra. These results highlight the utility of the MALDI-FT method for obtaining novel ion clusters and also show the stability of these clusters.

Metal-ion-assisted structural and anomeric analysis of Amadori compounds by electrospray ionization mass spectrometry.

RATIONALE: The Maillard reaction plays an important role in food, physiology and traditional Chinese medicine, and its primary reaction products are formed through Amadori rearrangement by reducing sugars and amino acids. The analysis of the characteristic fragmentation and of the glycosidic bond configuration of Amadori compounds will promote their fast discovery and identification by mass spectrometry. METHODS: Four Amadori compounds that reduce disaccharides and proline/tryptophan were used to investigate the fragmentation mechanisms via tandem mass spectrometry (MS/MS) with different alkali metal ion adducts. Cu2+ could be used to distinguish glycosidic bond configurations of the reducing disaccharides in the full-scan mass spectra. Quantum calculations were also conducted for a single Amadori compound with Cu2+ for analysis of the most optimized configurations and binding energies of metal complexes. RESULTS: MS/MS analysis of Amadori-alkali metal complexes revealed that the radius of the alkali metal ions had profound effects on the degree of fragmentation of such compounds, among which lithium-cationized ions produced the most extensive fragmentation. Amadori compounds with different glycosidic bonds formed differently proportioned metal complexes with Cu2+ , and the complexity of the copper complexes containing tryptophan moieties was higher than that of those containing proline moieties in the mass spectra. Quantum calculations showed that Amadori compounds with ß-configurations can form more binding sites with Cu2+ than those with α-configurations, thus making the metal complex with a single ligand more stable. In addition, the chelation of tryptophan with copper ions increased the coordination binding energy, which showed that α-configured Amadori compounds were readily able to form multi-ligand copper complexes. CONCLUSIONS: Metal-ion-assisted analysis provides crucial information for structural and anomeric analysis of Amadori compounds by electrospray ionization mass spectrometry. Elucidation of binding sites and binding energies by quantum calculations has significantly improved the knowledge of metal complexes in the gas phase and provides background information for determining the glycosidic configuration of Amadori isomers.

Computational Study of spx (x=1-3)-Hybridized Be-Be Bonds Stabilized by Amidinate Ligands.

Complexes containing odd-electron Be-Be bonds are still rare until now. Hereby, a series of neutral di-beryllium amidinate complexes containing a Be-Be bond were explored theoretically. The complexes with direct chelation with the Be2 dimer by the bidentate amidinate (AMD) ligands are always corresponding to their global minimum structures. The detailed bonding analyses reveal that the localized electrons of the Be-Be fragment can be adjusted by the amount of AMD ligands because each AMD ligand only takes one electron from the Be2 fragment. Meanwhile, the hybridization of the central Be atom also changes as the number of AMD ligands increases. In particular, the sp3 -hybridized single-electron Be-Be bond is firstly identified in the tri-AMD-ligands-chelated neutral D3h -Be2 (AMD)3 complex, which also possesses the higher stability compared to its monoanionic D3h -Be2 (AMD)3 - and monocationic C3 -Be2 (AMD)3 + analogues. Importantly, our study provides a new approach to obtain a neutral odd-electron Be-Be bond, namely by the use of radical ligands through side-on chelation.

In Situ Ligand Formation-Driven Synthesis of a Uranyl Organic Framework as a Turn-on Fluorescent pH Sensor.

A uranium-based metal-organic framework, [(UO2)(H2DTATC)] (HNU-39, H4DTATC = 5,5'-(9,10-dihydroxy-4a,9,9a,10-tetrahydroanthracene-9,10-diyl)diisophthalic acid) was successfully prepared by a hydrothermal method. The structure of HNU-39 comprises UO8 hexagonal bipyramids linked by doubly protonated DTATC ligands, forming a ribbon arrangement. It is worth noting that the DTATC ligand was transformed in situ from 5,5'-(anthracene-9,10-diyl)diisophthalic acid (H4DPATC) during the synthesis of HNU-39. Research on fluorescence properties has shown that HNU-39 exhibits fluorescence turn-on response under alkaline conditions and could be used as a potential pH sensor. Moreover, HNU-39 can also be successfully applied for pH sensing in real samples from a sewage treatment plant. The sensing mechanism can be interpreted as OH- ions reacting with the protons in the organic ligand of HNU-39.

All-Metallic Zn=Zn Double-π Bonded Octahedral Zn2 M4 (M=Li, Na) Clusters with Negative Oxidation State of Zinc.

Zn=Zn double bonded-especially double-π bonded-systems are scarce due to strong Coulomb repulsion caused by the Zn atom's internally crowded d electrons and very high energy of the virtual π orbitals in Zn2 fragments. It is also rare for Zn atoms to exhibit negative oxidation states within reported Zn-Zn bonded complexes. Herein, we report Zn=Zn double-π bonded octahedral clusters Zn2 M4 (M=Li, Na) bridged by four alkali metal ligands, in which the central Zn atom is in a negative oxidation state. Especially in D4h -Zn2 Na4 , the natural population analysis shows that the charge of the Zn atom reaches up to -0.89 |e| (-1.11 |e| for AIM charge). Although this cooperation inevitably increases the repulsion between two Zn atoms, the introduction of the s1 -type ligands results in occupation of degenerated π orbitals and the electrons being delocalized over the whole octahedral framework as well, in turn stabilizing the octahedral molecular structure. This study demonstrates that maintaining the degeneracy of the π orbitals and introducing electrons from equatorial plane are effective means to construct double-π bonds between transitional metals.

Be[triple bond, length as m-dash]Be triple bond in Be2X4Y2 clusters (X = Li, Na and Y = Li, Na, K) and a perfect classical Be[triple bond, length as m-dash]Be triple bond presented in Be2Na4K2.

Herein, we presented a series of Be2X4Y2 clusters (X = Li, Na and Y = Li, Na, K) containing Be[triple bond, length as m-dash]Be triple bonds, which were constructed by six alkali metals as electron-donating ligands. By virtue of the electrostatic potential mapping of the precedent Be[double bond, length as m-dash]Be double-π bonded D4h-Be2X4 clusters, the Be2X4Y2trans-bent geometries and the Be[triple bond, length as m-dash]Be triple bonds inside were both well interpreted. More remarkably, we first identified a perfect classical Be[triple bond, length as m-dash]Be triple bond in D4h-Be2Na4K2 and its Wiberg bond index of Be-Be (WBIBe-Be) reached up to 2.43. Meanwhile, our strategy provides a new approach to explain the trans-bent structure caused by terminal coordination.

Palladium(II) Acetylide Complexes with Pincer-Type Ligands: Photophysical Properties, Intermolecular Interactions, and Photo-cytotoxicity.

Two classes of cationic palladium(II) acetylide complexes containing pincer-type ligands, 2,2':6',2''-terpyridine (terpy) and 2,6-bis(1-butylimidazol-2-ylidenyl)pyridine (C^N^C), were prepared and structurally characterized. Replacing terpy with the strongly σ-donating C^N^C ligand with two N-heterocyclic carbene (NHC) units results in the PdII acetylide complexes displaying phosphorescence at room temperature and stronger intermolecular interactions in the solid state. X-ray crystal structures of [Pd(terpy)(C≡CPh)]PF6 (1) and [Pd(C^N^C)(C≡CPh)]PF6 (7) reveal that the complex cations are arranged in a one-dimensional stacking structure with pair-like PdII ⋅⋅⋅PdII contacts of 3.349 Šfor 1 and 3.292 Šfor 7. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to examine the electronic properties. Comparative studies of the [Pt(L)(C≡CPh)]+ analogs by 1 H NMR spectroscopy shed insight on the intermolecular interactions of these PdII acetylide complexes. The strong Pd-Ccarbene bonds render 7 and its derivative sufficiently stable for investigation of photo-cytotoxicity under cellular conditions.

Quantum Chemical Insight into the LiF Interlayer Effects in Organic Electronics: Reactions between Al Atom and LiF Clusters.

It is well known that the aluminum cathode performs dramatically better when a thin lithium fluoride (LiF) layer inserted in organic electronic devices. The doping effect induced by the librated Li atom via the chemical reactions producing AlF3 as byproduct was previously proposed as one of possible mechanisms. However, the underlying mechanism discussion is quite complicated and not fully understood so far, although the LiF interlayer is widely used. In this paper, we perform theoretical calculations to consider the reactions between an aluminum atom and distinct LiF clusters. The reaction pathways of the Al-(LiF)n (n = 2, 4, 16) systems were discovered and the energetics were theoretically evaluated. The release of Li atom and the formation of AlF3 were found in two different chemical reaction routes. The undissociated Al-(LiF)n systems have chances to change to some structures with loosely bound electrons. Our findings about the interacted Al-(LiF)n systems reveal new insights into the LiF interlayer effects in organic electronics applications.

Correction: Theoretical study and design of multifunctional phosphorescent platinum(ii) complexes containing triarylboron moieties for efficient OLED emitters.

Correction for 'Theoretical study and design of multifunctional phosphorescent platinum(ii) complexes containing triarylboron moieties for efficient OLED emitters' by Yong Wu et al., Phys. Chem. Chem. Phys., 2015, DOI: .

Theoretical study and design of multifunctional phosphorescent platinum(II) complexes containing triarylboron moieties for efficient OLED emitters.

The geometries, electronic structures, photophysical properties and spin-orbit coupling (SOC) effects in the radiative process for the recently synthesized complexes (Bppy)Pt(acac) (1) and (BNppy)Pt(acac) (2) as well as the designed complexes 3-6 were investigated by DFT and TD-DFT calculations, to reveal the influences of the functional ligands on charge injection ability and phosphorescence efficiency of emitters. It is found that compared with electron acceptor complex 1, complexes 2-6 have lower ionization potentials and comparable high electronic affinities, which are suited for bipolar luminescent materials. The results also demonstrated that Bppy complexes 1, 5 and 6 have more (3)MLCT compositions in T1 emitting states compared with BNppy complexes 2-4, which results in strong SOC and fast kr. Thus, the phosphorescence efficiency of 1 is higher than that of 2. In addition, 5 and 6 have the balanced charge transport and better hole injection ability when the hole-transporting ligand is incorporated to 1. Therefore, 5 and 6 can server as promising candidates for efficient multifunctional phosphorescent OLED emitters owing to their ambipolar characters, balanced charge carrier injection/transport features and high phosphorescence quantum efficiency.

Quantum chemical characterization and design of host materials based on phosphine oxide-substituted (triphenylamine) fluorene for (deep) blue phosphors in OLEDs.

We studied the electronic structures of a series of fluorene derivatives (p/mPODPFs and p/mPOAPFs) using density functional theory calculations and investigated their performances as host materials in organic light-emitting diodes from three aspects, i.e. triplet energy, ability of charge injection from neighboring organic layer or electrode, and match of the hosts and the reference guests (FIrpic and FCNIr) for efficient energy transfer (EF). Especially for the last aspect, the singlet/triplet (S(1)/T(1)) energies as well as the simulated host emission and guest absorption spectra are investigated to predict the possible emission mechanisms in the host-guest system and therefore to pursue the most suitable host for (deep) blue guest. From the investigated results, we deduced that pPODPF and pPOAPF are suitable for sky-blue FIrpic due to feasible Förster/Dexter energy transfers from pPODPF/pPOAPF to FIrpic, which agrees well with the experimental results. Furthermore, the higher external quantum efficiency (20.6%) of the pPOAPF-based device than that of the pPODPF-based device (13.2%) in experiments was inferred to be attributed to the matching S(1) energies between pPOAPF and FIrpic as well as good hole/electron injection abilities of pPOAPF in spite of a smaller overlap between the pPOAPF emission and FIrpic absorption spectra. By contrast, mPOAPF and mPODPF, designed in the work, may match with deep-blue FCNIr. In particular, mPOAPF may exhibit good performance as a host material for deep blue FCNIr as a consequence of its own balanced hole/electron injection ability and the matching S(1)/T(1) energies between mPOAPF and FCNIr.

Carbonyl amine/Schiff base ligands in manganese complexes: theoretical study on the mechanism, capability of NO release.

A compound having the capability of releasing NO upon exposure to visible or near-infrared (vis or NIR) light could be a potential candidate for photodynamic therapy (PDT), which is significant for humans. Here, we investigated a series of Mn(II) complexes (a-d) based on density functional theory (DFT) to illuminate the mechanism of their behavior of releasing NO. Their structural, spectroscopic, and photodissociable properties were calculated by quantum theoretical methods to give a detailed and warranted explanation of the performance of releasing NO. The results indicate that, for a-d, releasing NO was attributed to the electron transfer from d(yz)/d(xz)(Mn) orbitals to π*(NO) orbitals at the second excited triplet state (T(2)). Importantly, we confirmed the finding in the experiment that d could release NO upon exposure to the NIR region and, thus, may be a best candidate for PDT in a-d. Therefore, to take d for example, the analyses of the potential energy curves (PECs) of difference states and electron density difference between the T(2) and the ground state (S(0)) were performed to further provide evidence of ligand dissociation and release of NO at the T(2) state. Finally, we hope that our discussion can provide assistance to understand the behavior of the release of NO and design novel photodissociable transition metal nitrosyls for PDT applications.

Phenylcarbazole and phosphine oxide/sulfide hybrids as host materials for blue phosphors: effectively tuning the charge injection property without influencing the triplet energy.

Compared with red and green phosphorescent organic light-emitting diodes (PHOLEDs), efficient blue PHOLEDs are still scarce, because it is difficult for the host materials for blue phosphors to achieve a trade-off between a wide triplet energy and good charge injection properties. We theoretically studied a series of hybrid phosphine oxide/sulfide-phenylcarbazole host molecules (PO(S)PhCBZs) for blue phosphors through different linkage modes between phenylcarbazole (PhCBZ) and phosphine oxide/sulfide (PO/PS) moieties. The results indicate that the singlet excitons of all PO(S)-PhCBZs are delocalized over the entire molecule with intramolecular charge transfer (ICT) character and different linkage modes cause various degrees of ICT, which determines the injection abilities of carriers from neighboring layers following the order: PO-Phs (PO linked to the phenyl of PhCBZ) > para-POs (PO linked to the para-positions of PhCBZ) > meta-POs (PO linked to the meta-positions of PhCBZ). By contrast, the triplet excitons are confined to the carbazole unit for all PO(S)-PhCBZs. High triplet energies (E(T)) are therefore kept up for all systems, except for para-POs showing a slight drop in E(T) due to the delocalization of their triplet excitons to the phenyl moiety of PhCBZ. All hybrid PO(S)-PhCBZs, especially PO(s)-Phs, exhibit an enhancement in electron injection and triplet energy compared with the most widely used host material (N,N-dicarbazolyl-3,5-benzene) for blue PHOLEDs, and thereby have great potential for application in highly efficient light emitting diodes.

The origin of the unusual broad and intense visible absorption of tetrathiafulvalene-annulated zinc porphyrazine: a density functional theory study.

The vertical excitation energies of tetrathiafulvalene (TTF)-annulated zinc porphyrazine (ZnPzTTF) were investigated using time-dependent density functional theory (TDDFT) calculations and compared to the experimental UV-vis spectra. To examine the effects of the aza substitutions and TTF groups on the molecular properties, zinc complexes of porphyrin (ZnP), porphyrazine (ZnPz) and tetraTTF-annulated porphyrin (ZnPTTF) were also selected for comparison. It was shown that numerous electronic transitions with TTF-to-porphyrin or porphyrazine charge transfer character exist and the Q band of ZnPzTTF is dominated by TTF-to-porphyrazine charge transfer transition mixed with porphyrazine core unit itself except for classic porphyrazine π→π* transitions. The Q band of ZnPzTTF mixes with other configurations, which breaks down the Gouterman's classic four-orbital model for the spectral interpretation. The data suggest that TDDFT/SAOP performs best for Q and B bands of ZnPzTTF with the maximum error in excitation energy being 0.17 eV. The CAM-B3LYP, ωB97XD and M06-2X calculations qualitatively predict that the low-lying electronic transitions of ZnPzTTF with TTF-to-porphyrazine charge transfer character located below the Q band. The broad and intense red-shifted Q band suggests that ZnPzTTF can be a candidate for dye-sensitized solar cells.

Forward molecular design for highly efficient OLED emitters: a theoretical analysis of photophysical properties of platinum(II) complexes with N-heterocyclic carbene ligands.

The electronic structures and photophysical properties of eight Pt-complexes with different N-heterocyclic carbene ligands and potential to serve as light emitting diode materials were investigated by density functional theory and time-dependent density functional theory, employing the BP86 functional for geometry optimisations, SAOP potential for excited state calculations and all-electron TZ2P basis set throughout. Non-radiative and radiative decay rate constants were determined for each system through analyses of the geometric relaxations, d-orbital splitting and spin-orbit couplings at the optimised S(0) and T(1) geometries. Three Pt-systems bound to two N-heterocyclic carbenes were shown to be nonemissive, while a fourth was shown to be emissive from the T(1) excited state. Similar T(1)-initated emission was observed for three other Pt-systems investigated, each bound to four N-heterocyclic carbenes, while a fourth similarly tetra-ligated system showed T(2)-initation of emission. The results highlight the coupling of ligand-identity to photophysical properties and more importantly, the potential for rational optimisation and tuning of emission wavelengths and phosphorescent efficiencies. Encouragingly, two of the tetra-N-heterocyclic carbene ligated systems show strong potential to serve as highly-efficient blue and green light emitting materials, respectively.

Bottom-up synthesis of porous coordination frameworks: apical substitution of a pentanuclear tetrahedral precursor.

Top down goes bottom up: A family of microporous interpenetrating diamond frameworks can be constructed from a pentanuclear tetrahedral complex with nitrate groups at the apical positions as an inorganic precursor. A "bottom-up" methodology was used for substitution of the nitrate groups by linear ditopic carboxylate ligands (see picture). The Langmuir surface area of the resulting frameworks is higher than that of classical zeolites.