A cyclometalated N-heterocyclic carbene and acetylacetonate ligands in a phosphorescent Pt(II) dye for sensing glucose

New β-diketonate platinum (II) complexes, containing a cyclometalated N-heterocyclic carbene [Pt(Naph^C*iPr)(acac)] (3A) (HNaph^C*-κC* = 3-isopropyl-1-(naphthalen-2-yl)-1H-imidazole-2-ylidene), or a cyclometalated pyrazole, [Pt(Naph^Npz)(acac)] (3B) (HC^Npz = 1-(naphthalen-2-yl)-1H-pyrazole) and [Pt(Naph^Ndmpz)(acac)] (3B') (HC^Ndmpz = 1-(naphthalen-2-yl)-1H-3,5-dimethylpyrazole) have been prepared and characterized. Their absorption and emission properties in films of ethyl cellulose (EC) were determined along with those of the already reported for complex [Pt(Naph^C*Me)(acac)] (3A'). They showed that all four β-diketonate complexes display a bright phosphorescent emission with maxima in the blue region (λmax ∼ 480 nm for 3A and 3A'; 490 nm 3B and 3B'). The higher quantum yield (QY), longer decay times and greater oxygen sensitivity were exhibited by the Naph^C* derivatives, compared to the Naph^N ones. Polyacrylamide membranes with entrapped 3A' as dye, and glucose oxidase (GOx) enzyme were used for monitoring glucose level. The RSD is about 5% and the detection limit is at ∼5·10−4 M, with a response time usually of 10–15 min working in stop-flow mode. These platinum-based membranes respond reversibly to glucose for, at least, 20 measures. 3A’ is the first Pt(II) complex bearing a cyclometalated N-heterocyclic carbene ever used as dye for sensing glucose

The influence of cyclometalated ligand motifs on the solid-state assemblies and luminescent properties of Pt(II)-Tl(I) complexes

We have synthesized the HC^N ligand, 1-(naphthalen-2-yl)-1H-pyrazole (1A), and carried out its cyclometalation reaction with [{Pt(ν-CH)(μ-Cl)}] to give [{Pt(Naph^N)(μ-Cl)}]. This process takes place via the intermediate [Pt(ν-CH)Cl(HNaph^N-κN)] (2A) which could be isolated and fully characterized. Compound [{Pt(Naph^N)(μ-Cl)}] and the analogous N-heterocyclic carbene complex [{Pt(Naph^C*)(μ-Cl)}] (HNaph^C*-κC∗ = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) were used to prepare the bis-cyanide anionic derivatives NBu[Pt(Naph^E)(CN)] (E = N 4A, C* 4B) which subsequently react with TlPF to afford the corresponding complexes [PtTl(Naph^E)(CN)] (5A and 5B). The X-ray structures of 5A and 5B show the presence of 2D extended networks created by organometallic >PtTl(Naph^E)(CN)> entities, each one containing a Pt→Tl dative bond (d Pt-Tl = 3.0205(3) Å 5A, 2.9395(4) Å 5B). These units are linked together through additional Tl···NC and Tl···πcontacts, which, in the case of 5B, renders a stair-like arrangement. NBO charge distributions analysis on 4A and 4B shows a small negative charge on the Pt center for 4B, while positive for 4A, indicating the more electron donating character of the carbene with respect to the pyrazole group. Pt and C NMR spectra of NBu[Pt(Naph^E)(CN)] (E = N 4A′, C* 4B′) account for this difference. Photophysical analysis has been performed for 4A/B and 5A/B regarding the Naph^E fragment. The emissions of 4A and 4B in CHCl at 77 K present similar profiles and have been assigned to ILCT [π(Naph^E) → π*(Naph^E)] excited states. The green emission of 4A in poly(methyl methacrylate) (PMMA) film (5 wt %) affords a photoluminescence quantum yield (PLQY, φ) of 82%. In the solid state, the vibronic emissions of 5A (λ = 528 nm) and 5B (λ = 561 nm) are red-shifted in relation to their precursors (λ = 488 nm 4A, 530 nm 4B) and are mainly attributed to MM′LCT [d/s σ*(Pt,Tl) → π*(Naph^E)] excited states.This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades/FEDER (Project PGC2018-094749-B-I00), the Gobierno de Aragón (Grupo E17_17R), and Feder 2014-2020 (Construyendo Europa desde Aragón). S.P. thanks the Iran National Science Foundation and the Shiraz University Research Council for Grant nos. 95844501 and 93038832

A double rollover cycloplatinated(ii) skeleton: A versatile platform for tuning emission by chelating and non-chelating ancillary ligand systems

Described here is the synthesis and characterization of heteroleptic binuclear platinum(ii) complexes of the type [Pt(μ-bpy-2H)(S^S)] and [Pt(μ-bpy-2H)(L)(X)], containing a 2,2′-bipyridine-based double rollover cycloplatinated core (Pt(μ-bpy-2H)Pt), in combination with the anionic S^S chelate ligands di(ethyl)dithiocarbamate (dedtc) and O,O′-di(cyclohexyl)dithiophosphate (dcdtp) or non-chelating L/X ancillary ligands (PPh/Me, t-BuNC/Me, PPh/SCN and PPh/N). The new complexes were characterized using multinuclear (H, P and Pt) NMR spectroscopy and some of them additionally using single crystal X-ray diffraction. The absorption and photoluminescence of the complexes show a strong dependence on the ancillary ligands. Upon excitation at 365 nm, in a CHCl rigid matrix (77 K), the complexes exhibit structured emission bands with λ between 488 nm and 525 nm and vibrational spacing around 1350 cm, indicating the excited states centered on the cyclometalated ligand (ILCT) with some mixing MLCT characteristics. In the case of the PPh/N complex, a dual emission band (orange color) is observed in the solid state at 298 K for which the low energy band arises from an aggregation-induced emission (AIE). Upon lowering the temperature (77 K), thermochromism is observed (orange to yellow) which is accompanied by the intensification of the high energy band (ligand-centered structured band). Finally, in order to rationalize the obtained photophysical data, complete DFT (density functional theory) and TD-DFT (time-dependent DFT) calculations were performed on the selected complexes.The Shiraz University Research Council, the Iran National Science Foundation (grant no. 96010783), the Iran Science Elites Federation and the Spanish Ministerio de Economía y Competitividad (MINECO)/FEDER (Project CTQ2015-67461-P) provided financial support for this project

Phosphorescent cyclometalated Ir(iii) complexes comprising chelating thiolate ligands as pH-activatable sensors

A series of cyclometalated Ir(III) complexes possessing the general formula of [Ir(pqe)2(S^N)], pqe = 2-phenyl-quinoline-4-carboxylic acid methyl ester, S^N = pyridine-2-thiolate (Spy, B1); pyrimidine-2-thiolate (SpyN, B2); 5-(trifluoromethyl)-pyridine-2-thiolate (SpyCF3, B3); 2-thiazoline-2-thiolate (Stz, B4) and benzothiazole-2-thiolate (SBt, B5), were synthesized and characterized using several spectroscopies and analytical techniques. These compounds were photophysically investigated using UV-Vis absorption and photoluminescence spectroscopies. The complexes demonstrate strong red emissions in their CH2Cl2 solutions at 298 K but with different quantum efficiencies (B3 > B2 > B1 > B5 > B4). The emissions majorly originate from a 3MLCT (metal to ligand charge transfer) character along with smaller contributions of 3ILCT (intra ligand charge transfer) and 3L′LCT (ligand to ligand charge transfer; L = pqe, L′ = S^N). The esteric functional group (COOMe) on the pqe ligand can be easily converted to COO−Na+ in a hydrolysis process, resulting in the corresponding complexes [Na2{Ir(pqc)2(S^N)}], S^N = Spy, C1; SpyN, C2; SpyCF3, C3, being very water-soluble. Based on this hydrolysis, a large blue-shift is observed for the emissions of C1–C3 compared to B1–B5 which is supported by density functional theory (DFT) calculations. Also, the emission intensity of these complexes is sensitive to pH and steadily increases with the pH of solutions. The lifetime values as the other function of emission is changed by varying the pH values, wherein the graphs of lifetime/pH become quasi-linear. The slopes of the lines, as an index for the pH-sensitivity property, demonstrate the trend of C3 > C2 > C1 for the pH sensitivity of the complexes.This work was supported by the Institute for Advanced Studies in Basic Sciences (IASBS), Shiraz University, the Iran National Science Foundation (Grant Number: 99002060), Iran Science Elites Federation (ISEF) and the Spanish Ministerio de Ciencia, Innovación y Universidades/FEDER (Project PGC2018-094749-B-I00) and by the Gobierno de Aragón (Group E17_20R).Peer reviewe

Appendix A. Supplementary data: A cyclometalated N-heterocyclic carbene and acetylacetonate ligands in a phosphorescent Pt(II) dye for sensing glucose

The appendix file contains: Multinuclear NMR spectra, IR and mass spectra; crystal data and structure refinement; photophysical properties and TD-DFT calculations for 3B; oxygen sensing probes.Peer reviewe

A cyclometalated N-heterocyclic carbene and acetylacetonate ligands in a phosphorescent Pt(II) dye for sensing glucose

New β-diketonate platinum (II) complexes, containing a cyclometalated N-heterocyclic carbene [Pt(Naph^C*iPr)(acac)] (3A) (HNaph^C*-κC* = 3-isopropyl-1-(naphthalen-2-yl)-1H-imidazole-2-ylidene), or a cyclometalated pyrazole, [Pt(Naph^Npz)(acac)] (3B) (HC^Npz = 1-(naphthalen-2-yl)-1H-pyrazole) and [Pt(Naph^Ndmpz)(acac)] (3B') (HC^Ndmpz = 1-(naphthalen-2-yl)-1H-3,5-dimethylpyrazole) have been prepared and characterized. Their absorption and emission properties in films of ethyl cellulose (EC) were determined along with those of the already reported for complex [Pt(Naph^C*Me)(acac)] (3A'). They showed that all four β-diketonate complexes display a bright phosphorescent emission with maxima in the blue region (λmax ∼ 480 nm for 3A and 3A'; 490 nm 3B and 3B'). The higher quantum yield (QY), longer decay times and greater oxygen sensitivity were exhibited by the Naph^C* derivatives, compared to the Naph^N ones. Polyacrylamide membranes with entrapped 3A' as dye, and glucose oxidase (GOx) enzyme were used for monitoring glucose level. The RSD is about 5% and the detection limit is at ∼5·10−4 M, with a response time usually of 10–15 min working in stop-flow mode. These platinum-based membranes respond reversibly to glucose for, at least, 20 measures. 3A’ is the first Pt(II) complex bearing a cyclometalated N-heterocyclic carbene ever used as dye for sensing glucose.This work was supported by the Spanish Ministerio de Ciencia Innovacion y Universidades/FEDER (Projects PID2021-122869NB-I00 and PID2019-105408GB-I00), by the Gobierno de Aragon (Grupos E17_20R: Química Inorgánica y de los Compuestos Organometálicos, and E25_20R: Nanosensores y Sistemas Bioanalíticos) J. Camacho-Aguayo thanks the Government of Aragón for a grant.Peer reviewe

Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR3)], Vpy = 2-vinylpyridine and PR3 = PPh3 (1a); PPh2Me (1b); PPhMe2 (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow–orange region’s structured bands. The PPhMe2 derivative was the strongest emissive among the complexes, and the complex with PPh3 was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an SN2 mechanism. The complex with PPhMe2 ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh3 derivative showed the slowest one. Interestingly, for the PPhMe2 analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization