Gold(i)-doped films: new routes for efficient room temperature phosphorescent materials

Investigating the Impact of Packing and Environmental Factors on the Luminescence of Pt(N^N^N) Chromophores

Four Pt(II)(N^N^N) compounds featuring DMSO coordination at the fourth position were synthesized. Ligands varied in terms of pyridyl central ring (hydrogen/chlorine substituent) and lateral rings (triazoles with CF3 substitution or tetrazoles). Coordination to pyridine yielded tetra-nitrogen coordinated Pt(II) complexes or Pt-functionalized polymers using commercial 4-pyridyl polyvinyl (PV) or dimethylaminopyridine. Luminescence behaviors exhibited remarkable environmental dependence. While some of the molecular compounds (tetrazole derivatives) in solid state displayed quenched luminescence, all the polymers exhibited 3MMLCT emission around 600 nm. Conversely, monomer emission was evident on poly(methyl methacrylate) or polystyrene matrices. DFT calculations were used to analyze the aggregation of the complexes both at the molecular level and coordinated to the PV polymer and their influence on the HOMO-LUMO gaps.

Near-white light emission from single crystals of cationic dinuclear gold(I) complexes with bridged diphosphine ligands

Three cationic dinuclear Au(I) complexes containing acetonitrile (AN) as an ancillary ligand were synthesized: [μ-L_Me(AuAN)₂]·2BF₄ (1), [μ-L_Et(AuAN)₂]·2BF₄ (2), and [μ-L_iPr(AuAN)₂]·2BF₄ (3) (L_Me = {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, L_Et = {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and L_iPr = {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene}). The unique structures of complexes 1-3 with two P-Au(I)-AN rods bridged by rigid diphosphine ligands were determined through X-ray analysis. The Au(I)-Au(I) distances observed for complexes 1-3 were as short as 2.9804-3.0457 Å, indicating an aurophilic interaction between two Au(I) atoms. Unlike complexes 2 and 3, complex 1 incorporated CH₂Cl₂ into the crystals as crystalline solvent molecules. Luminescence studies in the crystalline state revealed that complexes 1 and 2 mainly exhibited bluish-purple phosphorescence (PH) at 293 K: the former had a PH peak wavelength at 415 nm with the photoluminescence quantum yield Φ_PL = 0.12, and the latter at 430 nm with Φ_PL = 0.13. Meanwhile, complex 3 displayed near-white PH, that is dual PH with two PH bands centered at 425 and 580 nm with Φ_PL = 0.44. The PH spectra and lifetimes of complexes 2 and 3 were measured in the temperature range of 77-293 K. The two PH bands observed for complex 3 were suggested to originate from the two emissive excited triplet states, which were in thermal equilibrium. From theoretical calculations, the dual PH observed for complex 3 is explained to occur from the two excited triplet states, T_1H and T_1L: the former exhibits a high-energy PH band (bluish-purple) and the latter exhibits a low-energy PH band (orange). The T_1H state is considered ³ILCT with a structure similar to that of the S₀-optimized structure. Conversely, the T_1L state is assumed to be a ³MLCT with a T₁-optimized structure, which has a short Au(I)-Au(I) bond and two bent rods (Au-AN). The thermal equilibrium between the two excited states is discussed based on computational calculations and photophysical data in the temperature range of 77-293 K. With regard to the crystal of complex 1, we were unable to precisely measure the temperature-dependent emission spectra and lifetimes, particularly at low temperatures, because the cooled crystals became irreversibly turbid over time.

Mono- and Dinuclear Gold(I) Coumarin Complexes: Luminescence Studies and Singlet Oxygen Production

The 4-(thiolmethyl)-7-(diethylamino)-2H-chromen-2-one ligand has been synthesized and used as chromophore in several mono- and dinuclear gold(I) compounds that contain a phosphane at the second coordination position. Four final products were able to obtain in pure form containing one coumarin and one phosphane ligand in the case of PTA (1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane) and PPh₃ (triphenylphosphine); one coumarin and two gold(I)-phosphane groups in the case of phosphane=DAPTA (3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) and two coumarin and two gold(I) atoms in the case of phosphane=DPEphos (bis[(2-diphenylphosphino)phenyl]ether), when it was used a diphosphane. Other diphosphane ligands used were not able to give the desired products in pure form. The luminescent properties of the compounds are governed by the fluorescence of the coumarin moiety in all compounds both for measurements carried out in solution and also immobilized in PMMA organic matrix. Phosphorescence emission can be detected in all cases at 77 K both for the uncoordinated coumarin ligand and the gold(I) derivatives, being more favoured in the presence of the gold(I) heavy atom. The compounds have been used as photosensitizers to generate ¹ O₂ with moderate quantum yields values.

Intra- vs Intermolecular Aurophilic Contacts in Dinuclear Gold(I) Compounds: Impact on the Population of the Triplet Excited State

Two series of dinuclear gold(I) complexes that contain two Au-chromophore units (chromophore = dibenzofurane or dimethylfluorene) connected through a diphosphane bridge that differs in the flexibility and length (diphosphane = dppb for 1,4-bis(diphenylphosphino)butane, DPEphos for bis[(2-diphenylphosphino)phenyl]ether, xanthphos for 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, and BiPheP for 2,2'-bis(diphenylphosphino)-1,1'-biphenyl) have been synthesized and structurally characterized. Their photophysical properties have been carefully investigated, paying attention to the role of the presence, or absence, of aurophilic contacts and their nature (intra- or intermolecular character). This analysis was permitted due to the X-ray crystallographic determination of all of the structures of the compounds discussed herein. The quantum yields of the triplet population, ϕ_T, have been calculated by nanosecond-laser flash photolysis measurements, and we could determine the main role of the character of the aurophilic contacts in the resulting ϕ_T, being especially favored in the presence of intermolecular contacts. Time-dependent density functional theory (TD-DFT) calculations support the absorption and emission assignments and the shorter distance between S₁ and the closest triplet excited state energy in the case of the compounds with a higher triplet-state population.

Digold(I) Thianthrenyl Complexes. Effect of Diphosphine Ligands on Molecular Structures in the Solid State and in Solution

A series of digold complexes possessing two thianthrenyl ligands, Au₂(Thi)₂(Ph₂P(CH₂) _n PPh₂) (Thi: 1-thianthrenyl; 1: n = 1, 2: n = 2, 3: n = 3, 4: n = 4), were prepared and characterized by crystallographic and spectroscopic measurements. X-ray crystallography of complexes 1 and 3 revealed U-shaped structures with short Au-Au distances [3.2171(3) Å and 3.0735(2) Å]. Complex 2 and three of the four structure-determined molecules of complex 4 showed structures without Au-Au contacts. UV-vis spectroscopic measurements of 1-4 and TD-DFT calculations of the two conformers of 1 revealed that complexes 1 and 3 in the solution phase contained conformers with Au(I)-Au(I) interactions in a much higher proportion than complexes 2 and 4. As a result, complexes with diphosphine ligands containing an odd number of methylene groups preferred structures with Au-Au interactions in the solid state and in solution. Oxidation of 1 with 2 equiv of PhICl₂ yielded a mixture of monomeric and dimeric thianthrenes and its dimer via ligand elimination and C-C coupling, respectively.

Fluorescent organic particle doped polymer-based gel dosimeter for neutron detection

The purpose of this work is to develop a material capable of detecting neutrons produced by photodisintegration in a linear accelerator for its medical use. In this study, we have developed a gel-like material doped with fluorescent organic particles. PPO at 1 wt% is used as primary dopant and POPOP as secondary one at 0.03 wt%. A set of four samples is produced, with boric acid concentrations of 0, 400, 800 and 1200 ppm. The viscoelastic properties of the material are characterized with rheological measurements, finding a gel-like behavior, i.e., a material that can keep its original shape if no stresses are applied, but can also be deformed by applying a moderate shear rate. Furthermore, the material was irradiated with gamma, electron, and neutron emission sources from ¹³⁷Cs, ²²Na, ⁶⁰Co, ²¹⁰Po, ⁹⁰Sr and ²⁴¹AmBe, and its response was measured in two different experimental settings, in two different institutions, for comparative purposes. From these measurements, one can clearly establish that the new material detects neutrons, electrons, and gammas within the MeV regions and below. Thus, our findings show that the developed material and its properties make it a promising technology for its use in a neutron detector.

Just Add the Gold: Aggregation-Induced-Emission Properties of Alkynylphosphinegold(I) Complexes Functionalized with Phenylene-Terpyridine Subunits

A series of organometallic complexes containing an alkynylphosphinegold(I) fragment and a phenylene-terpyridine moiety connected together by flexible linker have been prepared using the specially designed terpyridine ligands. The compounds were studied crystallographically to reveal that all of them contain a linearly coordinated Au(I) atom and a free terpyridine moiety. The different orientations of the molecules relative to each other in the solid state determine the multiple noncovalent interactions such as antiparallel ππ stacking, CH-π, and CH-Au, but no aurophilic interactions are realized. The organometallic Au(I) complexes obtained show fluorescence in the solution and dual singlet-triplet emission in the solid state. This means that their photophysical behavior is determined by both intermolecular lattice-defined interactions and Au(I) atom introduction. Density functional theory computational analysis supported the assignment of emission to intraligand electronic transitions only inside the phenylene-terpyridine part with no Au(I) involved. In addition, a study of the nature of the excited states for the "dimer" with an antiparallel orientation of the terpyridine fragment showed that this orientation leads to the generation of abstracted singlet and triplet states, lowering their energy in comparison with the monomer complex. Thus, the complexes obtained can be qualified as examples of Au(I)-containing organometallic aggregation-induced-emission luminogens.

Aggregation versus Biological Activity in Gold(I) Complexes. An Unexplored Concept

The aggregation process of a series of mono- and dinuclear gold(I) complexes containing a 4-ethynylaniline ligand and a phosphane at the second coordination position (PR3-Au-C≡CC6H4-NH2, complexes 1-5, and (diphos)(Au-C≡CC6H4-NH2)2, complexes 6-8), whose biological activity was previously studied by us, has been carefully analyzed through absorption, emission, and NMR spectroscopy, together with dynamic light scattering and small-angle X-ray scattering. These experiments allow us to retrieve information about how the compounds enter the cells. It was observed that all compounds present aggregation in fresh solutions, before biological treatment, and thus they must be entering the cells as aggregates. Inductively coupled plasma atomic emission spectrometry measurements showed that mononuclear complexes are mainly found in the cytosolic fraction; the dinuclear complexes are mainly found in a subsequent fraction composed of nuclei and cytoskeleton. Additionally, dinuclear complex 8 affects the actin aggregation to a larger extent, suggesting a cooperative effect of dinuclear compounds.

Continuous Flow Synthesis of [Au(NHC)(Aryl)] (NHC=N-Heterocyclic Carbene) Complexes

The use of weak and inexpensive bases has recently opened promising perspectives towards the simpler and more sustainable synthesis of Au(I)-aryl complexes with valuable applications in catalysis, medicinal chemistry, and materials science. In recent years, continuous manufacturing has shown to be a reliable partner in establishing sustainable and controlled process scalability. Herein, the first continuous flow synthesis of a range of Au(I)-aryl starting from widely available boronic acids and various [Au(NHC)Cl] (NHC=N-heterocyclic carbene) complexes in unprecedentedly short reaction times and high yields is reported. Successful synthesis of previously non- or poorly accessible complexes exposed fascinating reactivity patterns. Via a gram-scale synthesis, convenient process scalability of the developed protocol was showcased.

Base-assisted synthesis of 4-pyridinate gold(I) metallaligands: a study of their use in self-assembly reactions

The synthesis of di- and tritopic gold(i) metallaligands of the type [(Au4-py)2(μ2-diphosphane)] (diphosphane = bis(diphenylphosphanyl)isopropane or dppip (1), 1,2-bis(diphenylphosphanyl)ethane or dppe (2), 1,3-bis(diphenylphosphanyl)propane or dppp (3) and 1,4-bis(diphenylphosphanyl)butane or dppb (4)) and [(Au4-py)3(μ3-triphosphane)] (triphosphane = 1,1,1-tris(diphenylphosphanylmethyl)ethane or triphos (5) and 1,3,5-tris(diphenylphosphanyl)benzene or triphosph (6)) from [(AuCl)2(μ2-diphosphane)] or [(AuCl)3(μ3-triphosphane)] and 4-pyridylboronic acid in the presence of Cs2CO3 has been conducted. Interestingly, when [(AuCl)2(μ2-dppm)] (dppm = bis(diphenylphosphanyl)methane) was used as a starting material, the cyclic tetranuclear gold(i) compound [(Au4-py)2(CH)2{μ2-Au(PPh2)2}2] (I) was obtained instead. All the products have been characterized by IR and multinuclear NMR spectroscopy, mass spectrometry and elemental analysis and in the case of 1, 3, 5 and I by X-ray crystallography, which showed the presence of aurophilic interactions in all of them. The obtained metallaligands have been used as building blocks in self-assembly reactions with cis-blocked palladium or platinum acceptor moieties producing [2 + 2] metallamacrocycles or trigonal bipyramidal (TBP) [2 + 3] metallacages in good yields. The photophysical properties of both the metallaligands and the corresponding assemblies have been investigated.

Using Room Temperature Phosphorescence of Gold(I) Complexes for PAHs Sensing

The synthesis of two new phosphane-gold(I)–napthalimide complexes has been performed and characterized. The compounds present luminescent properties with denoted room temperature phosphorescence (RTP) induced by the proximity of the gold(I) heavy atom that favors intersystem crossing and triplet state population. The emissive properties of the compounds together with the planarity of their chromophore were used to investigate their potential as hosts in the molecular recognition of different polycyclic aromatic hydrocarbons (PAHs). Naphthalene, anthracene, phenanthrene, and pyrene were chosen to evaluate how the size and electronic properties can affect the host:guest interactions. Stronger affinity has been detected through emission titrations for the PAHs with extended aromaticity (anthracene and pyrene) and the results have been supported by DFT calculation studies.