Fluorescence Amplification of Unsaturated Oxazolones Using Palladium: Photophysical and Computational Studies.

Weakly fluorescent (Z)-4-arylidene-5-(4H)-oxazolones (1), ΦPL < 0.1%, containing a variety of conjugated aromatic fragments and/or charged arylidene moieties, have been orthopalladated by reaction with Pd(OAc)2. The resulting dinuclear complexes (2) have the oxazolone ligands bonded as a C^N-chelate, restricting intramolecular motions involving the oxazolone. From 2, a variety of mononuclear derivatives, such as [Pd(C^N-oxazolone)(O2CCF3)(py)] (3), [Pd(C^N-oxazolone)(py)2](ClO4) (4), [Pd(C^N-oxazolone)(Cl)(py)] (5), and [Pd(C^N-oxazolone)(X)(NHC)] (6, 7), have been prepared and fully characterized. Most of complexes 3-6 are strongly fluorescent in solution in the range of wavelengths from green to yellow, with values of ΦPL up to 28% (4h), which are among the highest values of quantum yield ever reported for organometallic Pd complexes with bidentate ligands. This means that the introduction of the Pd in the oxazolone scaffold produces in some cases an amplification of the fluorescence of several orders of magnitude from the free ligand 1 to complexes 3-6. Systematic variations of the substituents of the oxazolones and the ancillary ligands show that the wavelength of emission is tuned by the nature of the oxazolone, while the quantum yield is deeply influenced by the change of ligands. TD-DFT studies of complexes 3-6 show a direct correlation between the participation of the Pd orbitals in the HOMO and the loss of emission through non-radiative pathways. This model allows the understanding of the amplification of the fluorescence and the future rational design of new organopalladium systems with improved properties.

Thermally Activated Delayed Fluorescence in Neutral and Cationic Copper(I) Complexes with the 2-(4-Thiazolyl)benzimidazole Ligand.

Cationic [Cu(P^P)(Htbz)]PF6 [P^P = xantphos, dpephos; Htbz = 2-(4-thiazolyl)benzimidazole] and the corresponding neutral complexes [Cu(P^P)(tbz)], obtained through deprotonation of the diimine ligand, have been synthesized with the aim of analyzing the role of the diphosphane and Htbz deprotonation in the emissive properties of these complexes. For the study of the diphosphane effect, the luminescence properties of these compounds have been compared with those of the reported analogous derivatives with Htbz and carborane diphosphanes. Complexes [Cu(P^P)(Htbz)]PF6 (P^P = xantphos, dpephos) and [Cu(dpephos)(tbz)] display thermally activated delayed fluorescence, which has been studied, revealing a ΔE(S1-T1) between 658 and 455 cm-1. Theoretical calculations indicate different origins for the absorptions, leading to the observed emissions.

Closo- or Nido-Carborane Diphosphane as Responsible for Strong Thermochromism or Time Activated Delayed Fluorescence (TADF) in [Cu(N

Ortho-closo or ortho-nido-carborane-diphosphanes have been selected to prepare the heteroleptic cationic or neutral [Cu(N^N){(PPh2)2C2B10H10}]PF6 (1) and [Cu(N^N){(PPh2)2C2B9H10}] (2) [N^N = 2-(4-thiazolyl)benzimidazole], respectively. Complexes 1 and 2 display very different emissive behavior. Neutral complex 2 exhibits TADF (time activated delayed fluorescence) which has been studied both as powder and PMMA composite with similar ΔE(S1 - T1), τ(T1), and τ(S1) in both phases. Cationic complex 1 displays a much lower quantum yield than 2 and does not show TADF, but it exhibits a significant thermochromic luminescence, and its emission is very dependent on the medium. Theoretical studies show that metal-ligand (M-diphosphane) to ligand (L', diimine) transitions, MLL'CT, are responsible of the transitions which originate the emissive properties, but with very different contribution of the copper center, carborane cluster, and diphosphane phenyl rings for 1 and 2.

Reactivity of (Z)-4-Aryliden-5(4H)-thiazolones: [2 + 2]-Photocycloaddition, Ring-Opening Reactions, and Influence of the Lewis Acid BF3.

The irradiation of (Z)-2-phenyl-4-aryliden-5(4H)-thiazolones 2 with blue light (465 nm) in CH2Cl2 solution promotes [2 + 2]-photocycloaddition of the exocyclic C═C bonds and the formation of the dispirocyclobutanes 3. This reaction takes place with high stereoselectivity, given that the ε-isomer (1,3 head-to-tail syn coupling) is formed in more than 90% yield in most of the cases. However, irradiation of 5(4H)-thiazolones 2 with blue light (456 nm) in dry MeOH in the presence of BF3·OEt2 leads to the monospirocyclobutanes 4 with full stereoselectivity, also affording the ε-isomer. A ring-opening reaction of only one of the thiazolone rings appears to have taken place in 4 upon methanolysis, leading to the corresponding ester and thioamide groups. The treatment of free 4-aryliden-5(4H)-thiazolones 2 with a base in alcohol (NaOR/ROH) also produces a ring-opening reaction of the heterocycle by methanolysis, although, under these reaction conditions, further intramolecular S-attack at the exocyclic C(H)═C bond and cyclization is observed, forming the dihydrothiazoles 5 or 6 as mixtures of cis (RS/SR)- and trans (RR/SS)-isomers with high diastereomeric excess. trans-(RR/SS)-Dihydrothiazoles 6 can be isolated as pure diastereoisomers by column chromatography. Surprisingly, dihydrothiazoles 5 can also be obtained by the treatment of 4-aryliden-5(4H)-thiazolones 2 with BF3·OEt2 in methanol in the absence of a base.

Fluorescent Orthopalladated Complexes of 4-Aryliden-5(4H)-oxazolones from the Kaede Protein: Synthesis and Characterization.

The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4H)-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle and the ortho carbon of the arylidene ring. Two different 4-((Z)-arylidene)-2-((E)-styryl)-5(4H)-oxazolones, the structures of which are closely related to the chromophore of the Kaede protein and substituted at the 2- and 4-positions of the arylidene ring (1a OMe; 1b F), were used as starting materials. Oxazolones 1a and 1b were reacted with Pd(OAc)2 to give the corresponding dinuclear orthometalated palladium derivates 2a and 2b by regioselective C-H activation of the ortho-position of the arylidene ring. Reaction of 2a (2b) with LiCl promoted the metathesis of the bridging carboxylate by chloride ligands to afford dinuclear 3a (3b). Mononuclear complexes containing the orthopalladated oxazolone and a variety of ancillary ligands (acetylacetonate (4a, 4b), hydroxyquinolinate (5a), aminoquinoline (6a), bipyridine (7a), phenanthroline (8a)) were prepared from 3a or 3b through metathesis of anionic ligands or substitution of neutral weakly bonded ligands. All species were fully characterized and the X-ray determination of the molecular structure of 7a was carried out. This structure has strongly distorted ligands due to intramolecular interactions. Fluorescence measurements showed an increase in the quantum yield (QY) by up to one order of magnitude on comparing the free oxazolone (QY < 1%) with the palladated oxazolone (QY = 12% for 6a). This fact shows that the coordination of the oxazolone to the palladium efficiently suppresses the hula-twist deactivation pathway.

Tunable from Blue to Red Emissive Composites and Solids of Silver Diphosphane Systems with Higher Quantum Yields than the Diphosphane Ligands.

PMMA composites and solids of complexes of formulas [AgX(P-P)]n [n = 1 and 2; X = Cl, NO3, ClO4, CF3COO, and OTf; P-P = dppb, xantphos, (PR2)2C2B10H10 (R = Ph and iPr)] display the whole palette of colors from blue to red upon selection of the anionic ligand (X) and the diphosphane (P-P). The diphosphane seems to play the most important role in tuning the emission energy and thermally activated delayed fluorescence (TADF) behavior. The PMMA composites of the complexes exhibit higher quantum yields than that of the diphosphane ligands and those with dppb are between 28 and 53%. Remarkably, instead of blue-green emissions which dominate the luminescence of silver diphosphane complexes in rigid phases, those with carborane diphosphanes are yellow-orange or orange-red emitters. Theoretical studies have been carried out for complexes with P-P = dppb, X = Cl; P-P = dppic, X = NO3; P-P = dppcc, X = Cl, NO3, and OTf and the mononuclear complexes [AgX(xantphos)] (X = Cl, Br). Optimization of the first excited triplet state was only possible for [AgX(xantphos)] (X = Cl and Br). A mixed MLCT and MC nature could be attributed to the S0 → T1 transition in these three-coordinated complexes.

Decisive Influence of the Metal in Multifunctional Gold, Silver, and Copper Metallacycles: High Quantum Yield Phosphorescence, Color Switching, and Liquid Crystalline Behavior.

Three cyclic trinuclear pyrazolate complexes with Au(I), Ag(I), or Cu(I) have been studied. These complexes have interesting and distinct optical and thermal properties depending on the metal, namely, liquid crystalline behavior, red or deep-red phosphorescence at room temperature, thermoluminochromism, and response to silver ions. The selected ligand, 4-hexyl-3,5-dimethylpyrazolate, maximizes the effect that the nature of the metals has on the properties of the complexes, thus allowing the intermolecular metallophilic interactions to be responsible for the optical properties. Moreover, the gold and silver complexes show columnar liquid crystal phases at high temperature. All of the complexes have good solubility properties for processing as poly(methyl methacrylate) (PMMA) doped films. Films of the gold, silver, and copper complexes show interesting optical behavior such as wide-range color switching or phosphorescence turn-on upon cooling. In addition, films of the gold complex show a bright color switching (red to blue) in the presence of silver ions. The gold and copper complexes are bright phosphors with phosphorescent quantum yields of 90% in PMMA films, the highest values reported for this class of compounds at room temperature.

A comparative study of structural patterns and luminescent properties of silver-DAFO complexes with carborane- versus "classical"-diphosphanes.

New complexes with the DAFO (4,5-diazafluoren-9-one) ligand of stoichiometry [Ag(DAFO)(P-P)]OTf [P-P = dppe, 1,2-bis(diphenylphosphane)ethane; dppp, 1,3-bis(diphenylphosphane)propane; dppph, ortho-bis(diphenylphosphane)benzene; dppcc, 1,2-bis(diphenylphosphane)-1,2-dicarba-closo-dodecaborane; dipcc, 1,2-bis(diisopropylphosphane)-1,2-dicarba-nido-dodecaborane], [Ag(DAFO)(P-P*)] [P-P* = dppnc, 7,8-bis(diphenylphosphane)-7,8-dicarba-nido-undecaborate(-1); dipnc, 7,8-bis(diisopropylphosphane)-7,8-dicarba-closo-undecaborate(-1)] and [Ag(DAFO)(OTf)L] [L = PPh3; dpccMe, 1-diphenylphosphane-2-methyl-1,2-dicarba-closo-dodecaborane] are reported. The structures of the complexes depend on the skeleton of the diphosphane. Most of these compounds are luminescent and their emissions seem to have originated from IL (DAFO) transitions, modified upon coordination to silver.

Luminescent gold and silver complexes with the monophosphane 1-(PPh2)-2-Me-C2B10H10 and their conversion to gold micro- and superstructured materials.

Gold and silver complexes containing the monophosphane 1-PPh2-2-Me-l,2-C2B10H10 with different coordination numbers (2, 3) have been synthesized: [M(7,8-(PPh2)2-C2B9H10)(1-PPh2-2-Me-C2B10H10)] (M = Ag, Au) and [Au2(µ-1,n-C2B10H10)(1-PPh2-2-Me-C2B10H10)2] (n = 2, 12). Solid-state pyrolysis of [AuCl(1-PPh2-2-Me-C2B10H10)] and [Au2(µ-1,12-C2B10H10)(1-PPh2-2-Me-C2B10H10)2] in air and of solutions of [AuCl(1-PPh2-2-Me-C2B10H10)] deposited on silicon and silica at 800 °C results in single-crystal Au, confirmed by diffraction and SEM-EDS. The morphology of the pyrolytic products depends on the thermolytic conditions, and different novel 3-D superstructures or microcrystals are possible. We also propose a mechanism for the thermal conversion of these precursors to structural crystalline and phase pure materials. The presence of the carborane monophosphane seems to originate quenching of the luminescence at room temperature in the complexes [Au2(µ-1,n-C2B10H10)(1-PPh2-2-Me-C2B10H10)2], in comparison with other [Au2(µ-1,n-C2B10H10)L2] species (L = monophosphane).

Structural and photophysical study on heterobimetallic complexes with d8-d10 interactions supported by carborane ligands: theoretical analysis of the emissive behaviour.

Heterobimetallic complexes of formula [M{(PPh2)2C2B9H10}(S2C2B10 H10)M'(PPh3)] (M=Pd, Pt; M'=Au, Ag, Cu) and [Ni{(PPh2)2C2B9H10}(S2C2B10H10)Au(PPh3)] were obtained from the reaction of [M{(PPh2)2C2B10H10}(S2C2B10H10)] (M=Pd, Pt) with [M'(PPh3)](+) (M'=Au, Ag, Cu) or by one-pot synthesis from [(SH2C2B10H10], (PPh2 )2C2B10H10, NiCl2 ⋅6 H2 O, and [Au(PPh3)](+). They display d(8)-d(10) intermetallic interactions and emit red light in the solid state at 77 K. Theoretical studies on [M{(PPh2)2C2B9H10}(S2C2B10H10)Au(PPh3)] (M=Pd, Pt, Ni) attribute the luminescence to ligand (thiolate, L)-to-"P2-M-S2" (ML') charge-transfer (LML'CT) transitions for M=Pt and to metal (M)-to-"P2-M-S2" (ML') charge-transfer (MML'CT) transitions for M=Ni, Pd.

Diselenolate- and ditellurolate-carborane gold complexes.

Gold complexes with selenolate and tellurolate carborane ligands [E2C2B10H10](2-) (E = Se, Te) have been synthesized by reaction of a freshly prepared solution of [1,2-(LiE)2C2B10H10] (E = Se, Te) with [AuClL] (L = PPh3, PPh2Me, PPh2py) in a 1 : 2 molar ratio or [Au2Cl2(P∼P)] [P∼P = dppf, 1,1'-bis(diphenylphosphano)ferrocene; dppe, 1,2-bis(diphenylphosphano)ethane; dppc, 1,2-bis(diphenylphosphano)-o-carborane] in a 1 : 1 molar ratio affording complexes [Au2(µ-1,2-E2C2B10H10)L2] or [Au2(µ-1,2-E2C2B10H10)(P∼P)], respectively. The gold(III) species PPN[Au(E2C2B10H10)2] (PPN = bis(triphenylphosphano)iminium) have been afforded by reaction of PPN[AuCl4] with [1,2-(LiE)2C2B10H10]. Complex [Au4(µ-1,2-Se2C2B10H10)2(µ-dppc)2] displays a tetranuclear structure, different from the dinuclear cyclic arrangement proposed for other complexes with diphosphanes of [Au2(µ-1,2-Se2C2B10H10)(P∼P)] stoichiometry.

Influence of the group 11 metal on the emissive properties of complexes [M{(PR2)2C2B9H10}L].

The metal atoms in group 11 complexes [M{(PR2)2C2B9H10}L] [R = Ph, (i)Pr; L = tertiary phosphane; M = Au, Ag, Cu] play an important role in the emissive properties of these compounds. The influence of the metal follows the order Au ≫ Ag ≥ Cu. The three-coordinated complexes are obtained from the reaction of [AuClL], [Ag(OTf)L], or [Cu(NO3)(PPh3)2] with the closo carborane diphosphane in refluxing ethanol. For L = PPh2NHPy, cleavage of the P-N bond and the formation of the monophosphane PPh2OEt are observed, depending on the metal and the nido carborane diphosphane substituent ((i)Pr or Ph).

Iridium(III) complexes with polypyridine ligands coordinated as N-heterocyclic carbenes. Synthesis, structure and photophysical properties.

Unsaturated [Tp(Me2)Ir(III)] fragments, readily generated from compounds [Tp(Me2)Ir(C(6)H(5))(2)(N(2))], (1a) and [Tp(Me2)Ir(η(4)-CH(2)=C(Me)C(Me)=CH(2)] (1b) (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate), induce the isomerisation of the polypyridines, 2,2'-bipyridine, 1,10-phenanthroline and 2,2':6'2''-terpyridine, to form complexes that contain the carbene tautomer of these ligands. For terpy, a binuclear compound has also been isolated, in which this molecule bridges two Ir(III) centres, thanks to its coordination as a bidentate N-heterocyclic carbene. The new compounds have been structurally authenticated by X-ray crystallography and their photophysical properties have been investigated.

The structural diversity triggered by intermolecular interactions between Au(I)S2 groups: aurophilia and beyond.

The present study is aimed at elucidating the factors that direct the assembly of a specific family of Au(I) species. The assembly of Au(I) centers and dithiocarboxylato or xanthato ligands results in a surprising structural diversity observed by single-crystal X-ray diffraction. However, in solution, just evidences for discrete bimetallic [Au(2)L(2)] species have been observed. Interestingly, when dithiocarboxylato ligands have been used, a reversible supramolecular assembly has been observed forming the supramolecules of formulae [Au(2)L(2)](2) and [Au(2)L(2)](3). Initial studies on luminescent properties have been carried out at variable temperature. All the compounds show red emissions in the solid state at very similar energies, suggesting that the intramolecular interactions play a more relevant role in the luminescent properties than the intermolecular ones. The computational studies indicate that not only Au···Au interactions, but also Au···S and S···S ones play a role in the structure and energetic of the supramolecular species, as well as for the choice between supramolecular association or intramolecular oligomerization.

Emission tuning in dinuclear gold complexes with diphosphanes containing alkyne and/or oligophenylene spacers.

Reaction of the diphosphanes P∼P [PPh(2)(C(6)H(4))(n)PPh(2) (n = 1-5) and PPh(2)C[triple bond, length as m-dash]C(C(6)H(4))C[triple bond, length as m-dash]CPPh(2)] with [AuX(tht)] (X = Cl, C(6)F(5)) in a 1 : 2 molar ratio affords dinuclear luminescent complexes of formula [(AuX)(2)(P∼P)]. The photoemissive properties of these complexes are mainly controlled by the presence of the diphosphane ligand, specifically by the phenylene spacers of the diphosphanes. At room temperature fluorescent (IL) processes dominate the emissions, both in solution and in the solid state. Frozen solutions or solids at 77 K display dual emissions or only one emission attributed to ligand to ligand charge transfer (LL'CT) transitions from the auxiliary ligand (L) to phenylene spacers of the diphosphane (L').

Synthesis and characterisation of [6]-azaosmahelicenes: the first d4-heterometallahelicenes.

[6]-Azaosmahelicenes, the first d(4)-heterometallahelicenes, have been synthesised and fully characterised. Their optical properties (UV-Vis absorption and luminescence) are reported.

Highly emissive dinuclear complexes [Au2{µ-(PPh2)2C2B9H10}(C6F5)(PR3)] with different gold fragments coordinated to an anionic diphosphine.

Reaction of the yellow-green emitters [Au{(PPh(2))(2)C(2)B(9)H(10)}(PR(3))] with [Au(C(6)F(5))(tht)] affords orange-red emissive gold complexes [Au(2){µ-(PPh(2))(2)C(2)B(9)H(10)}(C(6)F(5))(PR(3))] which contain different neutral (PR(3)) and anionic (C(6)F(5)) auxiliary ligands and an anionic diphosphine. The resulting complexes are among the few reported in which an ortho-carborane diphosphine acts in a bridging mode, and are unique in containing not a closo- (neutral), but a nido-carborane (anionic) cluster. DFT and TDDFT calculations led to the prediction of the origin of the two first singlet-triplet transitions, which is consistent with the experimental results. Although the blue emissive nido-diphosphine plays a key role in the transitions of the three-coordinate precursors and the final dinuclear complexes, it is the environment around the gold centre that controls the emission energy.

Unprecedented luminescent heteropolynuclear aggregates with gold thiolates as building blocks.

The reaction of [AuCl(P-N)], in which P-N represents a heterofunctional phosphine ligand, with pentafluorothiophenol, HSC(6)F(5), gives the thiolate gold derivatives [Au(SC(6)F(5))(P-N)] (P-N = PPh(2)py (1), PPh(2)CH(2)CH(2)py (2), or PPhpy(2) (3)). Complex [Au(SC(6)F(5))(PPh(2)py)] (1) reacts with [Au(OTf)(PPh(2)py)] in a 1:1 or 1:2 molar ratio to afford the di- or trinuclear species [Au(2)(µ-SC(6)F(5))(PPh(2)py)(2)]OTf (4) and [Au(3)(µ(3)-SC(6)F(5))(PPh(2)py)(3)](OTf)(2) (5), with the thiolate acting as a doubly or triply bridging ligand. The reactivity of the mononuclear compounds [Au(SC(6)F(5))(P-N)] toward silver or copper salts in different ratios has been investigated. Thus, the treatment of [Au(SC(6)F(5))(P-N)] with Ag(OTf) or [Cu(NCMe)(4)]PF(6) in a 1:1 molar ratio gives complexes of stoichiometry [AuAg(OTf)(µ-SC(6)F(5))(P-N)] (P-N = PPh(2)py (6), PPh(2)CH(2)CH(2)py (7), or PPhpy(2) (8)) or [AuCu(µ-SC(6)F(5))(P-N)(NCMe)]PF(6) (P-N = PPh(2)py (9), PPh(2)CH(2)CH(2)py (10), or PPhpy(2) (11)). These complexes crystallize as dimers and display different coordination modes of the silver or copper center, depending on the present functionalized phosphine ligand. The treatment of [Au(SC(6)F(5))(PPh(2)py)] with silver and copper compounds in other molar ratios has been carried out. In a 2:1 ratio, the complexes [Au(2)M(µ-SC(6)F(5))(2)(µ-PPh(2)py)(2)]X (M = Ag, X = OTf (12); M = Cu, X = PF(6) (13)) are obtained. The same reaction in a 4:3 molar ratio affords the species [Au(4)M(2)(µ-SC(6)F(5))(3)(µ-PPh(2)py)(4)]X(3) (M = Ag, X = OTf (14); M = Cu, X = PF(6) (15)). The crystal structures of some of these complexes reveal different interactions among the metallic d(10) centers. The complexes display dual emission. The band at higher energy has been attributed to intraligand (IL) transitions, and the one at lower energy has been assigned to a ligand to metal (LM) charge transfer process. The latter emission is modulated by the heterometal (silver or copper).

Synthesis, structural characterization, photophysical properties and theoretical analysis of gold(I) thiolate-phosphine complexes.

A series of luminescent dinuclear neutral complexes of stoichiometry [(AuSPh)(2)(PPh(2)-(C(6)H(4))(n)-PPh(2))] (n = 1, 2, 3) as well as their tetranuclear cationic derivatives [(Au(2)SPh)(2)(PPh(2)-(C(6)H(4))(n)-PPh(2))(2)](PF(6))(2) are reported. Their crystal structures have been elucidated by X-ray studies. These studies indicate that, for the dinuclear species, only when n = 1 the molecules exhibit intermolecular aurophilic interactions. None of the tetranuclear species crystallizes in their molecular form, due to the formation of aggregates through Au···Au interactions. The origin of the luminescence has been analyzed by computational studies indicating that the presence or absence of aurophilic interactions does not affect the luminescent behavior and that intraligand charge transfer processes which involve the thiolate and the diphosphine are responsible for the emissions. The result is in contrast with the thiolate-gold charge transfer processes which dominate the photophysics of gold-thiolate compounds and reveals the influence of the phenylene spacers in the emissive behavior of these compounds.