Dynamic Motions of Ligands around the Metal Centers Afford a Fidget Spinner-Type AIE Luminogen.

A new type of aggregation-induced emission (AIE) luminogen containing a dimeric metal fragment and two or three phthalazine ligands is described, which shows dynamic motions of ligands around the metal centers in solution. Based on the variable-temperature and EXSY NMR spectroscopy data, X-ray crystallography structures, and computational results, three different pathways (i.e., reversible exchange with haptotropic shifts, circulation of ligands around the dimeric metal fragment, and walking on the spot of ligands on the metal centers) were considered for this dynamic behavior. Restriction of these dynamic processes in the aggregate forms of the compounds (in H2O/CH3CN solvent mixtures) contributes to their AIE. DFT calculations and NMR analysis showed that bright excited states for these molecules are not localized on isolated molecules, and the emission of them stemmed from π-dimers or π-oligomers. The morphologies and the mode of associations in the solvent mixtures were determined by using transmission electron microscopy (TEM) and concentration-dependent NMR spectroscopy. The computational results showed the presence of a conical intersection (CI) between the S0 and S1 excited state, which provides an accessible pathway for nonradiative decay in these systems.

Perylene bisimide-based nanocubes for selective vapour phase ultra-trace detection of aniline derivatives.

Rapid and selective detection of biomarkers at trace levels is a highly coveted objective in the early diagnosis of cancer. Herein, we disclose the design and synthesis of a polyhedral oligomeric silsesquioxane (POSS) substituted perylene diimide. This compound is fully characterized in solution by multi nuclear NMR, as well as in gas state by ESI-MS. Surprisingly, solid-state characterization revealed an unusual cubic morphology with particle dimensions of 80-160 nm. Fluorescence studies indicate that the bulky POSS units effectively prevent perylene's aggregation caused quenching, yielding quantum yields as high as 92%. Exposing the sensor droplet-cast on quartz to anline and o-toluidine, two important biomarkers for lung cancer, results in very highly reproducible, reversible and selective fluorescence quenching responses, with LODs as low as 19 and 8 ng L-1, and linear ranges of 65-350 and 25-450 ng L-1 respectively. Mechanistic investigations point to photoinduced electron transfer (PET) as the operative pathway responsible for fluorescence quenching.

Metal-Organic Cubane Cage with Trimethylplatinum(IV) Vertices.

Herein we describe the synthesis and characterization of the first platinum(IV) metal-organic cage [(Me3PtIV)8(byp)12](OTf)8 (2), in which the organometallic moieties trimethylplatinum(IV) (PtMe3) occupied the corners of a cubane structure and 4,4'-bipyridine ligands used as linkers. The first-principles density functional theory calculations showed that the highest occupied molecular orbitals were localized on the PtMe3 moieties, while the lowest unoccupied molecular orbitals were distributed on the organic linkers.

Bis-N-Heterocyclic Carbene Complexes of Coinage Metals Containing Four Naphthalimide Units: A Structure-Emission Properties Relationship Study.

Naphthalimide derivatives provide highly versatile self-assembled systems and aggregated forms with fascinating emission properties that make them potential candidates for many applications such as bioimaging and sensing. Although various aggregated species of naphthalimide derivatives have been well documented, little is known about the correlation between their structure and photophysical properties. Here the preparation of a series of tetrameric naphthalimide molecules in which naphthalimide units are linked by bis-N-heterocyclic carbene complexes of coinage metals is described. An in-depth structural investigation into these tetramers has been carried out in solution and the solid state using spectroscopic methods, X-ray crystallography, and computational methods. The experimental and calculated data indicate that the magnitude of the intramolecular interchromophoric π-interactions increases either by an increase in the metal ionic radius or on going from the solid to the solution state. These tetrameric naphthalimide compounds show intramolecular excimeric emissions in the solid and solution phases. However, the quantum yield efficiencies of these excimeric emissions show a trend similar to that for the intramolecular π-interactions either by going from the solution to the solid state or with an increase in the metal ionic radius. Surprisingly, the amine derivative analogues of the silver(I) compound showed an unusual increase in the emission quantum yield efficiency to 92% in solution due to intramolecular hydrogen bonds between amine substituents on adjacent naphthalimde units.

Five- and Six-Coordinated Silver(I) Complexes Formed by a Metallomacrocyclic Ligand with a "Au2N2" Donor Group: Observation of Pendulum and Linear Motions and Dual Phosphorescence.

The six-coordinated silver(I) complex [Au2Ag(µ-(PPh2)2py)2(OTf)2](OTf), 4 (py = pyridine, OTf = CF3SO3), and the five-coordinated silver(I) complex [Au2Ag(acetone)(µ-(PPh2)2py)2](PF6)3, 6, were prepared by the reaction of the precursor complexes 1(OTf)2 and 1(PF6)2, in which 1 = [Au2(µ-(PPh2)2py)2]2+, with 1 equiv of Ag(OTf) in dichloromethane and excess of Ag(PF6) in a mixture of dichloromethane/acetone, respectively. Also, the five-coordinated silver(I) complex [Au2Ag(µ-(PPh2)2py)2(py)(OTf)](OTf)2, 5, was obtained by the reaction of 4 with pyridine. The clusters 4-6 were characterized using multinuclear NMR spectroscopy and elemental microanalysis. The single-crystal X-ray diffraction analysis revealed the octahedral and distorted square pyramidal geometries around the silver(I) centers in the crystal structures of 4 and 6, respectively; a dynamic structure was observed for cluster 5 due to pendulum motion of the Ag(pyridine) moiety, which was anchored in the metallomacrocyclic unit [Au2(µ-(PPh2)2py)2]2+. Although the crystal structure of 6 did not display disorders for the silver atom and the acetone ligand similar to that observed for 5, the low-temperature NMR spectroscopies and calculations show a dynamic structure for cluster 6 due to linear motion of the Ag(acetone) moiety. The reaction of the precursor complex 1(PO2F2)2 with 2 equiv of Ag(PO2F2) yielded the tetranuclear Au2Ag2 cluster [Au2Ag2(PO2F2)2(µ-(PPh2)2py)2](PO2F2)2, 7, with a planar-shaped {Au2Ag2} metal core in which alternating Au and Ag atoms occupy the tetragon vertices and showed a strong argentophillic interaction between the silver(I) centers. All clusters 4-7 are emissive in the solid state, and the origins of their emissive excited states were determined using time-dependent density functional theory calculations. Cluster 7 showed a dual phosphorescence emission, which displays strong dependence of the contributions of each emissive component onto the excitation wavelength.

Tetranuclear Au2Cu2 Clusters with Butterfly- and Planar-Shaped Metal Cores: Strong Rigidochromism Induced by Jahn-Teller Distortion in Two-Coordinated Gold(I) Centers.

Two tetranuclear Au2Cu2 cluster complexes [Au2Cu2(µ-(PPh2)2py)2(µ-OH)](PF6)3, 2, and [Au2Cu2Cl2(µ-(PPh2)2 py)2](OTf)2, 4, have been prepared by the reactions of precursor complexes [Au2(µ-(PPh2)2py)2](OTf)2, 1, and [Cu2(µ-(PPh2)2py)2(µ-SMe2)(OTf)2], 3, with [Cu(NCCH3)4]PF6 and AuCl(SMe2), respectively. The crystal structures of complexes 2 and 4 were determined by X-ray crystallography, indicating a butterfly-shaped Au2Cu2 metal core for 2 and a planar-shaped Au2Cu2 metal core for 4. In complex 2, the Cu atoms occupy the edge-sharing bond, while in complex 4, alternating Au and Cu atoms occupy the tetragon vertices. The optical properties of the complexes were investigated by experimental and computational methods. Although complex 2 displayed a luminescence vapochromic behavior in the presence several volatile organic compounds, complex 4 indicated only an distinguishable change in its emission color when it was exposed to vapor of hydrogen-bond donor solvents. The calculations showed that 2 undergoes an unsymmetrical distortion in its two-coordinated gold(I) centers upon excitation to the first triplet excited state. This distortion induces a large Stokes shift and a strong rigidochromism behavior that is unprecedented for two-coordinated gold(I) complexes.

Stimuli-responsive emissive behavior of 1- and 1,3-connectivities in azulene-based imine ligands: cycloplatination and Pt-Tl dative bond formation.

The preparation of two new azulene-based imine ligands N-(2,6-diisopropylphenyl)-6-tBu-1-azulenylmethaneimine, 3, and N-(2,6-diisopropylphenyl)-6-tBu-3-(2,6-diisopropylphenyliminomethyl)-1-azulenylmethaneimine, 4, is described. These imine ligands display stimuli responsive emissive behavior and their fluorescence can be switched on and off by protonation and neutralization with trifluoroacetic acid and trimethylamine, respectively. The cyclometalation of the monoimine ligand by platinum gave the cyclometalated complex [PtMe(SMe2)(3')], 5, (where the prime denotes the cyclometalated ligand 3). The reaction of 5 with TlPF6 yields the trinuclear bent Pt2Tl complex {[PtMe(SMe2)(3')]2(µ-Tl)}PF6, 6, via Pt-Tl dative bonds. The compounds 3-6 were characterized using NMR spectroscopy and the solid-state structures of 5 and 6 were further determined by X-ray crystallography. The electronic absorption spectra of the species 3-H+, 4-H+, 5 and 6 were obtained and compared with those observed for the parent species 3 and 4. DFT and TD-DFT calculations are used to elucidate the origin of the electronic transitions in monoimine ligand 3 and its protonated form 3-H+.

Cyclometalated heteronuclear Pt/Ag and Pt/Tl complexes: a structural and photophysical study.

To investigate the factors influencing the luminescent properties of polymetallic cycloplatinated complexes a detailed study of the photophysical and structural properties of the heteronuclear complexes [Pt2Me2(bhq)2(µ-dppy)2Ag2(µ-acetone)](BF4)2, 2, [PtMe(bhq)(dppy)Tl]PF6, 3, and [Pt2Me2(bhq)2(dppy)2Tl]PF6, 4, [bhq = benzo[h]quinoline, dppy = 2-(diphenylphosphino)pyridine] was conducted. Complexes 3 and 4 synthesized by the reaction of [PtMe(bhq)(dppy)], 1, with TlPF6 (1 or 1/2 equiv.) and stabilized by unsupported Pt-Tl bonds as revealed by multinuclear NMR spectroscopy and confirmed by X-ray crystallography for 3. DFT calculations for the previously reported butterfly Pt2Ag2 cluster 2 reveal that in the optimized geometry the bridging acetone molecule is removed and the metal core displays a planar-shaped geometry in which according to a QTAIM calculation and natural bond orbital (NBO) analysis the Ag···Ag metallophilic interaction is strengthened. In contrast to the precursor 1, which is only emissive in glassy solutions ((3)MLCT 485 nm), all 2-4 heteropolynuclear complexes display intense emissions in the solid state and in glassy solutions. Time-dependent density functional theory (TD-DFT) is used to elucidate the origin of the electronic transitions in the heteronuclear complexes 2 and 3. The low energy absorption and intense orange emission for cluster 2 (solid 77 K and glass) are attributed to metal-metal to ligand charge transfer (MM'LCT) with a minor L'LCT contribution. For 3 and 4 two different bands are developed: the high energy band (602-630 nm) observed for 4 at 77 K (solid, glass) and in diluted glasses for 3 is ascribed to emission from discrete Pt2Tl units of mixed (3)L'LCT/(3)LM'CT origin. However, the low energy band (670-690 nm) observed at room temperature (solid) for both complexes and also in concentrated glasses for 3 is assigned to (3)ππ excited states arising from intermolecular interactions.

A highly efficient luminescent Pt2Tl2 chain with a short Tl(I)-Tl(I) interaction.

The preparation of an unsupported tetranuclear cluster with a linear Pt(0)-Tl(I)-Tl(I)-Pt(0) metal chain is described. The complex shows strong red emission in the solid state, having a quantum yield of 73%. Density functional theory (DFT) and time-dependent DFT calculations show that red emission originated from a platinum to thallium-thallium charge-transfer excited state.

Synthesis, structure and photophysical properties of binuclear methylplatinum complexes containing cyclometalating 2-phenylpyridine or benzo{h}quinoline ligands: a comparison of intramolecular Pt-Pt and π-π interactions.

The binuclear cyclometalated complexes [Pt(2)Me(2)(ppy)(2)(µ-dppm)], 1a, and [Pt(2)Me(2)(bhq)(2)(µ-dppm)], 1b, in which ppy = 2-phenylpyridyl, bhq = benzo{h}quinoline and dppm = bis(diphenylphosphino)methane, were synthesized by the reaction of [PtMe(SMe(2))(ppy)] or [PtMe(SMe(2))(bhq)] with 1/2 equiv of dppm at room temperature, respectively. Complexes 1a and 1b were fully characterized by multinuclear ((1)H, (31)P, (13)C, and (195)Pt) NMR spectroscopy and were further identified by single crystal X-ray structure determination. A comparison of the intramolecular Pt-Pt and π-π interactions in complexes 1a and 1b has been made on the basis of data on crystal structures and wave functions analysis. The binuclear complexes 1a and 1b are luminescent in the solid state, and showing relatively intense orange-red emissions stemming from (3)MMLCT excited states. The reaction of complex 1b with excess MeI gave the binuclear cyclometalated Pt(IV)-Pt(IV) complex [Pt(2)Me(4)(bhq)(2)(µ-I)(2)], 2. Crystal structure of complex 2 shows intermolecular C-H···I and C-H···π interactions in solid state.

Organoplatinum(II) complexes containing chelating or bridging bis(N-heterocyclic carbene) ligands: formation of a platinum(II) carbonate complex by aerial CO2 fixation.

The preparation of two new bis(N-heterocyclic carbene) platinum(II) complexes, in which NHC rings are joined by a CH(2) linker group, is described. While, the chelate complex [PtMe(2)(bis-NHC1)], 1, was formed with large tert-butyl wingtips, the iso-propyl N-substituent analogue favors formation of the cluster complex [Pt(2)Me(4)(µ-SMe(2))(µ-bis-NHC2)](2)(µ-Ag(2)Br(2)), 2, in which two binuclear platinum(II) complexes are linked together by an Ag(2)Br(2) unit. The chelating platinum complex 1 undergoes aerial CO(2) fixation and forms platinum(II) carbonate complex [Pt(CO(3))(bis-NHC1)], 3.

Cyclometalated organoplatinum(II) complexes: first example of a monodentate benzo[h]quinolyl ligand and a complex with bridging bis(diphenylphosphino)ethane.

The cyclometalated complexes [Pt(ppy)R(SMe(2))] or [Pt(bhq)R(SMe(2))], where ppyH = 2-phenylpyridine, bhqH = benzo[h]quinoline and R = methyl or p-tolyl, react with bis(diphenylphosphino)ethane, dppe, in a 1:1 ratio to give the corresponding complexes [Pt(κ(1)-C-ppy)R(dppe)] or [Pt(κ(1)-C-bhq)R(dppe)], in which the ppy or bhq ligands are monodentate and dppe is chelating. The similar reaction in a 2:1 ratio gives the binuclear complexes [{Pt(ppy)R}(2)(µ-dppe)] or [{Pt(bhq)R}(2)(µ-dppe)], in which the dppe ligands are in the unusual bridging bidentate bonding mode.

Associative and dissociative mechanisms in the formation of phthalazine bridged organodiplatinum(II) complexes.

The reaction of phthalazine with the binuclear organoplatinum complexes [Me(2)Pt(µ-SMe(2))(µ-dppm)PtR(2)], R = Me, Ph, 4-tolyl or R(2) = (CH(2))(4), dppm = bis(diphenylphosphino)methane, gives the corresponding complexes [Me(2)Pt(µ-phthalazine)(µ-dppm)PtR(2)] by displacement of the bridging dimethylsulfide ligand. The structures of [Me(2)Pt(µ-SMe(2))(µ-dppm)PtMe(2)] and [Me(2)Pt(µ-phthalazine)(µ-dppm)PtMe(2)] have been determined. Kinetic studies show that the reactions occur mostly by a second order reaction when R = Me or R(2) = (CH(2))(4) but entirely by a first order reaction when R = Ph or 4-tolyl. Evidence is presented that the reactions when R = Me or R(2) = (CH(2))(4) can occur by either associative or dissociative mechanisms but that the reactions when R = Ph or 4-tolyl occur only by an unusual dissociative mechanism involving formation of an intermediate with a donor-acceptor Pt-Pt bond.

Oxidative addition reaction of diarylplatinum(II) complexes with MeI in ionic liquid media: a kinetic study.

A kinetic study of the oxidative addition reaction of diarylplatinum(II) complexes [Pt(p-MeC(6)H(4))(2)(NN)] (1a: NN = 1,10-phenanthroline (phen) and 1b: NN = 4,4'-di-tert-butyl-2,2'-bipyridine ((t)Bu(2)bpy)) with MeI in ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][bta]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) is described. The reactions were investigated as a function of MeI concentration and temperature under pseudo-first-order conditions using UV-vis spectroscopy techniques. In general, the oxidative addition reactions in ionic liquids followed an S(N)2 mechanism, similar to that reported for the related reactions in conventional solvents, e.g. benzene or acetone. The reaction rates in different solvents followed the order acetone > ionic liquids > benzene. The trend in the values of k(2) clearly indicated that ionic liquids behave like conventional solvents and that no particular 'ionic liquid effect' was detected in this kind of reaction. The effect of solvent on the reactions was examined using a linear solvation energy relationship (LSER) based on the Kamlet-Taft solvent scale. The activation parameters, DeltaH(++) and DeltaS(++), were obtained for the reactions in each solvent and the investigation of enthalpy-entropy compensation confirmed that the mechanism operated in all solvents is similar.

Cyclometalated cluster complex with a butterfly-shaped Pt2Ag2 core.

The cyclometalated platinum complex [PtMe(bhq)(dppy)] (1), in which bhq = benzo{h}quinoline and dppy = 2-(diphenylphosphino)pyridine, was prepared by the reaction of [PtMe(SMe(2))(bhq)] with 1 equiv of dppy at room temperature. Complex 1 contains one free pyridyl unit and was readily characterized by multinuclear NMR spectroscopy and elemental microanalysis. The reaction of complex 1 with 1 equiv of [Ag(CH(3)CN)(4)]BF(4) gave the cyclometalated cluster complex [Pt(2)Me(2)(bhq)(2)(mu-dppy)(2)Ag(2)(mu-acetone)](BF(4))(2) (2) in 70% yield. The crystal structure of complex 2 was determined by X-ray crystallography, indicating a rare example of a butterfly cluster with a Pt(2)Ag(2) core in which the Ag atoms occupy the edge-sharing bond. In solution, the bridging acetone dissociates from the cluster complex 2, but as shown by NMR spectroscopy, the Pt(2)Ag(2) core is retained in solution and a dynamic equilibrium is suggested to be established between the planar and butterfly skeletal geometries.

Binuclear cyclometalated organoplatinum complexes containing 1,1'-bis(diphenylphosphino)ferrocene as spacer ligand: kinetics and mechanism of MeI oxidative addition.

The binuclear complex [Pt2Me2(ppy)2(mu-dppf)], 1, in which ppy = deprotonated 2-phenylpyridyl and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(ppy)] with 0.5 equiv of dppf at room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-kappa1C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt2I2Me4(ppy)2(mu-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(mu-dppf)PtIMe2(ppy)], 4, and complex 3 was obtained. In a comparative study, the reaction of [PtMe(SMe2)(ppy)] with 1 equiv of monodentate phosphine PPh3 gave [PtMe(ppy)(PPh3)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe2I(ppy)(PPh3)], C. All the complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy, and complex 2 was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex 1 with excess MeI was monitored by low temperature 31P NMR spectroscopy and further by 1H NMR spectroscopy, and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers. In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV) intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5 times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh 3 in the complex A, has significantly enhanced the electron richness of the platinum centers.

Oxidative addition of methyl iodide to a new type of binuclear platinum(II) complex: a kinetic study.

A new organodiplatinum(II) complex cis,cis-[Me2Pt(mu-NN)(mu-dppm)PtMe2] (1), in which NN = phthalazine and dppm = bis(diphenylphosphino)methane, is synthesized by the reaction of cis,cis-[Me2Pt(mu-SMe2)(mu-dppm)PtMe2] with 1 equiv of NN. Complex 1 has a 5d(pi)(Pt) --> pi(imine) metal-to-ligand charge-transfer band in the visible region, which was used to easily follow the kinetics of its reaction with MeI. Meanwhile, the complex contains a robust bridging dppm ligand that holds the binuclear integrity during the reaction. A double MeI oxidative addition was observed, as shown by spectrophotometry and confirmed by a low-temperature 31P NMR study. The classical S(N)2 mechanism was suggested for both steps, and the involved intermediates were suggested. Consistent with the proposed mechanism, the rates of the reactions at different temperatures were slower in benzene than in acetone and large negative deltaS values were found in each step. However, some abnormalities were observed in the related rate constants and deltaS values, which were demonstrated to be due to the associative involvement of the polar acetone molecules in the reactions. The rates are almost 6 times slower in the second step as compared to the first step because of the electronic effects transmitted through the ligands and the steric effects.