Browsing by Subject "Luminiscencia"
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- PublicationOpen AccessInfluence of Ancillary Ligands and Isomerism on the Luminescence of Bis-cyclometalated Platinum(IV) Complexes(ACS, 2016-08-01) Juliá Hernández, Fabio; García-Legaz, María Dulce; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis, characterization, and photophysical properties of a wide variety of bis-cyclometalated Pt(IV) complexes featuring a C2-symmetrical or unsymmetrical {Pt(ppy)2} unit (sym or unsym complexes, respectively; ppy = C-deprotonated 2-phenylpyridine) and different ancillary ligands are reported. Complexes sym-[Pt(ppy)2X2] (X = OTf–, OAc–) were obtained by chloride abstraction from sym-[Pt(ppy)2Cl2] using the corresponding AgX salts, and the triflate derivative was employed to obtain homologous complexes with X = F–, Br–, I–, trifluoroacetate (TFA–). Complexes unsym-[Pt(ppy)2(Me)X] (X = OTf–, F–) were prepared by reacting unsym-[Pt(ppy)2(Me)Cl] with AgOTf or AgF, respectively, and the triflate derivative was employed as precursor for the synthesis of the homologues with X = Br–, I–, or TFA– through its reaction with the appropriate anionic ligands. The previously reported complexes unsym-[Pt(ppy)2X2] (X = Cl–, Br–, OAc–, TFA–) are included in the photophysical study to assess the influence of the arrangement of the cyclometalated ligands. Density functional theory (DFT) and time-dependent DFT calculations on selected derivatives were performed for a better interpretation of the observed excited-state properties. Complexes sym-[Pt(ppy)2X2] (except X = I–) exhibit phosphorescent emissions in fluid solutions at 298 K arising from essentially 3LC(ppy) excited states, which are very similar in shape and energy. However, their efficiencies are heavily dependent on the nature of the ancillary ligands, which affect the energy of deactivating ligand-to-ligand charge transfer (LLCT) or ligand-to-metal charge transfer (LMCT) states. The fluoride derivative sym-[Pt(ppy)2F2] shows the highest quantum yield of this series (Φ = 0.398), mainly because the relatively high metal-to-ligand charge transfer admixture in its emitting state leads to a high radiative rate constant. Complexes unsym-[Pt(ppy)2X2] emit from 3LC(ppy) states in frozen matrices at 77 K, but their emissions are totally quenched in fluid solution at 298 K because of the presence of low-lying, dissociative LMCT excited states, which also cause photoisomerization reactions. Complexes unsym-[Pt(ppy)2(Me)X] (X = F–, Cl–, Br–, TFA–) show strong emissions in fluid solutions at 298 K (Φ = 0.52–0.63) because deactivating LMCT states lie at high energies. However, derivative unsym-[Pt(ppy)2(Me)I] is only weakly emissive at 298 K because of the presence of low-lying LLCT [p(I) → π*(ppy)] states.
- PublicationOpen AccessLuminescent halido(aryl) Pt(IV) complexes obtained via oxidative addition of iodobenzene or diaryliodonium salts to bis-cyclometalated Pt(II) precursors.(2021-09-09) López López, Juan Carlos; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis of bis-cyclometalated halido(aryl) Pt(IV) complexes [PtX(Ar)(C^N)2], with C^N = cyclometalated 4-(tert-butyl)-2-phenylpyridine (bppy), 2-(p-tolyl)pyridine (tpy), 2-(2-thienyl)pyridine (thpy), or 1-phenylisoquinoline (piq), X = I, Cl, or F, and Ar = Ph (for all C^N ligands) or t-BuPh (for C^N = tpy), and the photophysical properties of the chlorido and fluorido series is reported. The oxidative addition of iodobenzene to cis-[Pt(C^N)2] precursors is demonstrated to occur in MeCN under irradiation with visible light to give complexes [PtI(Ph)(C^N)2], presumably involving radical species that also produce the activation of the solvent to give cyanomethyl complexes [PtI(CH2CN)(C^N)2]. The introduction of an aryl ligand can also be achieved by reacting cis-[Pt(C^N)2] with (Ar2I)PF6 (Ar = Ph, t-BuPh), which affords cationic intermediates of the type [Pt(Ar)(C^N)2(NCMe)]+. The subsequent addition of an iodide or chloride salt gives the corresponding iodido- or chlorido(aryl) complexes. The fluorido(aryl) derivatives can be obtained from the iodido complexes by halide exchange using AgF. The chlorido- and fluorido(aryl) complexes display intense phosphorescence in deaerated CH2Cl2 solution and poly(methyl methacrylate) (PMMA) films at 298 K from triplet excited states primarily localized on the cyclometalated ligands (3LC) with a small MLCT admixture. Compared with the chlorido complexes, the fluorido derivatives consistently present significantly shorter emission lifetimes and higher radiative and nonradiative rate constants due to a greater MLCT contribution to the emissive state. In contrast, the introduction of the t-BuPh group did not induce significant changes in radiative rates with respect to the phenyl complexes.
- PublicationOpen AccessLuminescent platinum (II) Complexes with Terdentate N∧C∧C Ligands(2023-12-05) Poveda Otazo, Dionisio; Vivancos Ureña, Ángela; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis, structure, and luminescence of Pt(II) complexes of the type [Pt(N∧C∧C)(L)] are reported, where N∧C∧C is a terdentate ligand resulting from the cycloplatination of 2-(3,5-diphenoxyphenyl)pyridine or 2-(4,4″-dimethyl-[1,1′:3′,1″-terphenyl]-5′-yl)pyridine, and L represents a monodentate ancillary ligand, which can be γ-picoline, 4-pyridinecarboxaldehyde, PPh3, n-butyl or 2,6-dimethylphenyl isocyanide, CO, or the N-heterocyclic carbenes 1-butyl-3-methylimidazol-2-ylidene or 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene. Derivatives bearing CO, isocyanides, or carbenes showed the highest stabilities in solution, whereas the pyridine and PPh3 derivatives establish ligand-exchange equilibria in acetonitrile. Different supramolecular structures are observed in the solid state, which largely depend on the nature of the ancillary ligand. Isocyanides and CO favor π interactions between the aromatic rings, metallophilic Pt···Pt contacts, or a combination of both. In contrast, pyridine ligands may lead to bimolecular assemblies driven by C–H···O, C–H···Pt, or C–H/π hydrogen bonds. Luminescence was examined in fluid solution, poly(methyl methacrylate) matrices, and the solid state at 298 K, and in 2-methyltetrahydrofuran glasses at 77 K. The majority of derivatives show highly efficient emissions from 3ILCT/MLCT or 3ILCT/MLCT/LLCT excited states of monomeric species. The formation of excimers and different types of emissive aggregates are demonstrated, which lead to red-shifted emissions of different origins and characteristics depending on the
- PublicationOpen AccessLuminescent platinum(IV) complexes bearing cyclometalated 1,2,3-triazolylidene and bi- or terdentate 2,6-diarylpyridine ligands(Wiley, 2019-04-23) Vivancos Ureña, Ángela; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis, structure, and photophysical properties of luminescent PtIV complexes that combine cyclometalated 1,2,3-triazolylidene and bi- or terdentate 2,6-diarylpyridine ligands are reported. The targeted complexes represent the first examples of PtIV species with a cyclometalated mesoionic aryl-NHC ligand. They exhibit moderate or weak emissions in fluid solution at 298 K arising from 3LC states, which become very intense in poly(methyl methacrylate) (PMMA) matrices at 298 K. DFT and TD-DFT calculations confirm that the chromophoric ligand is the cyclometalated 2,6-diarylpyridine and show that the aryl-NHC ligand exerts a beneficial effect on the emission efficiencies of these derivatives by increasing the energy of deactivating LMCT excited states with respect to comparable PtIV complexes with cyclometalated 2-arylpyridine ligands.
- PublicationOpen AccessPhosphorescent biaryl platinum(iv) complexes obtained through double metalation of dibenzoiodolium ions(Royal Society of Chemistry, 2022-03-15) López López, Juan Carlos; Bautista, Delia; González Herrero, Pablo; Química Inorgánica
- PublicationOpen AccessPhosphorescent Tris-cyclometalated Pt(IV) Complexes with Mesoionic N‐Heterocyclic Carbene and 2‐Arylpyridine Ligands(2022-07-21) Vivancos Ureña, Ángela; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis, structure, photophysical properties, and electrochemistry of the first series of Pt(IV) tris-chelates bearing cyclometalated aryl-NHC ligands are reported. The complexes have the general formula [Pt(trz)2(C∧N)]+, combining two units of the cyclometalated, mesoionic aryl-NHC ligand 4- butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene (trz) with a cyclometalated 2-arylpyridine [C∧N = 2-(2,4-difluorophenyl)- pyridine (dfppy), 2-phenylpyridine (ppy), 2-(p-tolyl)pyridine (tpy), 2-(2-thienyl)pyridine (thpy), 2-(9,9-dimethylfluoren-2-yl)- pyridine (flpy)], and presenting a mer arrangement or metalated aryls. They exhibit a significant photostability under UV irradiation and long-lived phosphorescence in the blue to yellow color range, arising from 3LC excited states involving the C∧N ligands, with quantum yields of up to 0.34 in fluid solution and 0.77 in the rigid matrix at 298 K. The time-dependent density functional theory (TD-DFT) calculations reveal that nonemissive, deactivating excited states of ligand-to-metal charge-transfer (LMCT) character are pushed to high energies as a consequence of the strong σ-donating ability of the carbenic moieties, making the Pt(trz)2 subunit an essential structural component that enables efficient emissions from the chromophoric C∧N ligands, with potential application for the development of different Pt(IV) emitters with tunable properties.
- PublicationOpen AccessPhotochemically induced cyclometalations at simple platinum(II) precursors(American Chemical Society, 2023-04-12) Poveda Otazo, Dionisio; Vivancos Ureña, Ángela; Bautista, Delia; González Herrero, Pablo; Química InorgánicaPhotochemical cycloplatinations of 2-arylpyridines and related C∧N ligands, as well as terdentate heteroaromatic N∧N∧C, N∧C∧N, and N∧C∧C compounds, are demonstrated using (Bu4N)2[Pt2Cl6] or [PtCl2(NCPh)2] as precursors at room temperature. Mono- or bis-cyclometalated Pt(II) complexes with C∧N ligands are obtained depending on excitation wavelength and precursor. Monitoring experiments show that photoexcitation enables both the N-coordination and the subsequent C–H metalation. Photochemical synthetic protocols have been developed, which are advantageous with respect to the established thermal procedures and have allowed the synthesis of the first Pt(II) complexes with N∧C∧C ligands.
- PublicationOpen AccessPhotoinduced Reductive C–C and C–Heteroatom Couplings from Bis-cyclometalated Pt(IV) Alkynyl Complexes(2023-08-24) López López, Juan Carlos; Bautista, Delia; González Herrero, Pablo; Química InorgánicaUnsymmetrical dicarboxylato complexes [Pt(tpy)2(O2CR)2] [tpy = cyclometalated 2-(p-tolyl)pyridine, R = Me, CF3] react with the terminal alkynes 4-methoxyphenylacetylene, phenylacetylene, 4-(trifluoromethyl)phenylacetylene or 3,5-difluorophenylacetylene in the presence of a base to produce complexes mer-[Pt(tpy)2(O2CR)(CCAr)], in which the metalated carbon atoms are in a meridional arrangement. Irradiation of the trifluoroacetato derivatives with a 365 nm LED source leads to isomerization to the facial complexes, which can be converted to chlorido derivatives upon reaction with NH4Cl. In contrast, irradiation of the acetato derivatives leads to four different processes, namely, reduction to cis-[Pt(tpy)2], annulations involving one of the tpy ligands and the Cα and Cβ atoms of the alkynyl to give benzoquinolizinium derivatives, isomerization to the facial geometry, or C–O couplings between the acetato ligand and one tpy. The first two processes are favored by the presence of electron-donating groups on the alkynyl, whereas electron-withdrawing groups favor the last two. Irradiation of complexes fac-[Pt(tpy)2(O2CCF3)(CCAr)] with a medium-pressure Hg UV lamp leads to a reductive C–C coupling involving the alkynyl Cα atom and one of the tpy ligands to give pyridoisoindolium derivatives, except for the methoxyphenylacetylide derivative, which is photostable. On the basis of TDDFT calculations, the photoreactivity of the mer complexes is attributed to 3LLCT [π(alkynyl) → π*(tpy)] excited states for annulations or 3LMCT [π(alkynyl) → dσ*] excited states for the rest of the processes, which are accessible through thermal population from 3LC(tpy) states. The C–C couplings from the fac complexes are attributed to photoreactive pentacoordinate intermediates.
- PublicationOpen AccessSelective synthesis, reactivity and luminescence of unsymmetrical bis-cyclometalated Pt(IV) complexes(Royal Society of Chemistry, 2019-09-18) Vivancos Ureña, Ángela; Poveda Otazo, Dionisio; Muñoz, Alonso; Moreno, Julia; Bautista, Delia; González Herrero, Pablo; Química InorgánicaPt(II) complexes cis-N,N-[PtCl(C^N)(N′^C′H)], where C^N represents a monocyclometalated 2,6-diaryl- or 2-arylpyridine ligand and N′^C′H is an N-coordinated 2-arylpyridine, are selectively obtained from bridge-cleavage reactions of dimers [Pt2(μ-Cl)2(C^N)2] with excess N′^C′H at room temperature; isolation and characterization of derivatives of this kind is reported for the first time. Oxidation with PhICl2 affords Pt(IV) complexes [PtCl2(C^N)(C′^N′)], bearing two cyclometalated ligands in an unsymmetrical arrangement. The abstraction of the two chlorides using AgOTf at 120 °C in the presence of an additional 2-arylpyridine ligand leads to mer isomers of tris-cyclometalated Pt(IV) complexes if C^N derives from a 2-arylpyridine, whereas it results in a reductive C–C coupling if C^N is a monocyclometalated 2,6-diarylpyridine. Complexes [PtCl2(C^N)(C′^N′)] show phosphorescence in frozen PrCN glasses arising from essentially 3LC excited states localized on the cyclometalated ligand with the lowest π–π* transition energy. The combined photophysical data and computational results substantiate a variable degree of MLCT admixture into the emitting state depending on the atom trans to the metalated carbon of the chromophoric ligand (Cl or N), which has an appreciable effect on the characteristics of the observed luminescence.
- PublicationOpen AccessStrongly luminescent Pt(IV) complexes with a Mesoionic N-Heterocyclic Carbene Ligand: tuning their photophysical properties.(2021-02-09) Vivancos Ureña, Ángela; Jiménez García, Adrián; Bautista, Delia; González Herrero, Pablo; Química InorgánicaThe synthesis, electrochemistry, and photophysical properties of a series of bis-cyclometalated Pt(IV) complexes that combine the mesoionic aryl-NHC ligand 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene (trz) with either 1-phenylpyrazole or 2-arylpyridine (C∧N) are reported. The complexes (OC-6-54)-[PtCl2(C∧N)(trz)] bearing cyclometalating 2-arylpyridines present phosphorescent emissions in the blue to yellow color range, which essentially arise from 3LC(C∧N) states, and reach quantum yields of ca. 0.3 in fluid solutions and almost unity in poly(methyl methacrylate) (PMMA) matrices at 298 K, thus representing a class of strong emitters with tunable properties. A systematic comparison with the homologous C2-symmetrical species (OC-6-33)-[PtCl2(C∧N)2], which contains two equal 2-arylpyridine ligands, shows that the introduction of a trz ligand leads to significantly lower nonradiative decay rates and higher quantum efficiencies. Computational calculations substantiate the effect of the carbene ligand, which raises the energy of dσ* orbitals in these derivatives and results in the higher energies of nonemissive deactivating 3LMCT states. In contrast, the isomers (OC-6-42)-[PtCl2(C∧N)(trz)] are not luminescent because they present a 3LMCT state as the lowest triplet.
- PublicationOpen AccessVisible light driven generation and alkyne insertion reactions of stable bis-cyclometalated Pt(iv) hydrides(2020-10-13) Poveda Otazo, Dionisio; Vivancos Ureña, Ángela; Bautista, Delia; González Herrero, Pablo; Química InorgánicaHydride complexes resulting from the oxidative addition of C–H bonds are intermediates in hydrocarbon activation and functionalization reactions. The discovery of metal systems that enable their direct formation through photoexcitation with visible light could lead to advantageous synthetic methodologies. In this study, easily accessible dimers [Pt2(μ-Cl)2(C^N)2] (C^N = cyclometalated 2-arylpyridine) are demonstrated as a very convenient source of Pt(C^N) subunits, which promote photooxidative C–H addition reactions with different 2-arylpyridines (N′^C′H) upon irradiation with blue light. The resulting [PtH(Cl)(C^N)(C′^N′)] complexes are the first isolable Pt(IV) hydrides arising from a cyclometalation reaction. A transcyclometalation process involving three photochemical steps is elucidated, which occurs when the C^N ligand is a monocyclometalated 2,6-diarylpyridine, and a detailed analysis of the photoreactivity associated with the Pt(C^N) moiety is provided. Alkyne insertions into the Pt–H bond of a photogenerated Pt(IV) hydride are also reported as a demonstration of the ability of this class of compounds to undergo subsequent organometallic reactions.