Chromo- and Fluorogenic Organometallic Sensors

Compounds that change their absorption and/or emission properties in the presence of a target ion or molecule have been studied for many years as the basis for optical sensing. Within this group of compounds, a variety of organometallic complexes have been proposed for the detection of a wide range of analytes such as cations (including H+), anions, gases (e.g. O 2, SO2, organic vapours), small organic molecules, and large biomolecules (e.g. proteins, DNA). This chapter focuses on work reported within the last few years in the area of organometallic sensors. Some of the most extensively studied systems incorporate metal moieties with intense long-lived metal-to-ligand charge transfer (MLCT) excited states as the reporter or indicator unit, such as fac-tricarbonyl Re(I) complexes, cyclometallated Ir(III) species, and diimine Ru(II) or Os(II) derivatives. Other commonly used organometallic sensors are based on Pt-alkynyls and ferrocene fragments. To these reporters, an appropriate recognition or analyte-binding unit is usually attached so that a detectable modification on the colour and/or the emission of the complex occurs upon binding of the analyte. Examples of recognition sites include macrocycles for the binding of cations, H-bonding units selective to specific anions, and DNA intercalating fragments. A different approach is used for the detection of some gases or vapours, where the sensor's response is associated with changes in the crystal packing of the complex on absorption of the gas, or to direct coordination of the analyte to the metal centre

Dérivés ferrocéniques : Détection électrochimique et optique de cations en solution et étude des interactions ligand-cation

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Détection d'ions en solution, équilibres complexes ligand ferrocénique-cation, et spectroscopie de masse

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Homoleptic and heteroleptic Ru-II complexes with extended phenanthroline-based ligands

Four Ru-II complexes of general formula [Ru(PT)(3)](2+), [Ru(NT)(3)](2+), [Ru(PT)(bpy)(2)](2+), and [Ru(NT)(bpy)(2)](2+), where PT = 10,13-bis((triisopropylsilyl)ethynyl)dipyrido[3,2-a:2',3'-c]phenazine, NT = 10,15-bis((triisopropylsilyl)ethynyl)benzo[i]dipyrido[3,2-a:2',3'-c]phenazine and bpy = 2,2'-bipyridine have been synthesized. Their electrochemical and photophysical properties have been studied, with the aid of DFF and TD-DFT theoretical methods. The extended phenanthroline ligand PT exhibits two reduction processes at -0.98 and -1.55 (versus SCE) and no clearly detectable oxidation processes; the more extended analogue NT is substantially easier to reduce by about 300 mV. In the four complexes, the two first reduction processes are centered on the extended phenanthroline ligands, and, according to DFT calculations, also oxidations are likely to be located on such moieties. PT and NT exhibit green-yellow fluorescence at 298 and 77K with photoluminescence quantum yields of 3.4% and 62.1%, respectively, at room temperature. At 77 K, a strong and long-lived phosphorescence is detected only for PT (lambda(max) = 658 nm, tau = 29 ms). In oxygen-free solution at 298 K [Ru(PT)(3)](2+) and [Ru(PT)(bpy)(2)](2+) exhibit a very weak emission band with lambda(max) about 700 nm, which extends towards the near infrared region and is unambiguously attributed to emission from the lowest triplet level centered on the PT ligand; its emission intensity is strongly enhanced at 77 K where lifetimes of 724 and 767 ns are measured for [Ru(PT)(3)](2+) and [Ru(PT)(bpy)(2)](2+), respectively. The two complexes with the NT ligand show no triplet emission as observed for the PT analogues, but only a faint fluorescence signal attributable to negligible amounts of free ligand in solution. Photophysical data are fully rationalized with DFF methods, which always predict that the lowest triplet excited state is centered on the extended phenanthroline ligand in all of the investigated R-II complexes. The estimated energy of the lowest triplet level of the PT-based compounds is in good agreement with the experimental value determined from the phosphorescence spectra. Moreover, the theoretical model rationalizes the lack of phosphorescence for the NT series, because the lowest triplet is estimated to be at 0.97 eV above the ground state (approximate to 1280 nm), where non-radiative deactivations prevail. (C) 2014 Elsevier Ltd. All rights reserved

“Heteroleptic Copper(I) Complexes Coupled with Methano[60]fullerene: Synthesis, Electrochemistry, and Photophysics”

Heteroleptic copper(I) complexes CuPOP-F and CuFc-F have been prepared from a fullerene-substituted phenanthroline ligand and bis[2-(diphenylphosphino) phenyl] ether (POP) and 1,1′-bis(diphenylphosphino)ferrocene (dppFc), respectively. Electrochemical studies indicate that some ground-state electronic interaction between the fullerene subunit and the metal-complexed moiety are present in both CuPOP-F and CuFc-F. Their photophysical properties have been investigated by steady state and time-resolved UV-vis-NIR luminescence spectroscopy and nanosecond laser flash photolysis in a CH2Cl 2 solution and compared to those of the corresponding model copper(I) complexes CuPOP and CuFc and of the fullerene model compound F. Selective excitation of the methanofullerene moiety in CuPOP-F results in regular deactivation of the lowest singlet and triplet states, indicating no intercomponent interactions. Conversely, excitation of the copper(I)-complexed unit (405 nm, 40% selectivity) shows that the strongly luminescent triplet metal-to-ligand charge-transfer (3MLCT) excited state located at 2.40 eV is quenched by the carbon sphere with a rate constant of 1.6 × 10 8 s-1. Details on the mechanism of photodynamic processes in CuPOP-F via transient absorption are hampered by the rather unfavorable partition of light excitation between the two chromophores. By determination of the yield of formation of the lowest fullerene triplet level through sensitized singlet oxygen luminescence in the NIR region, it is shown that the final sink of photoinduced processes is always the fullerene triplet. This can be populated via a two-step charge-separation charge-recombination process and a less favored 3MLCT→3C60 triplet-triplet energy-transfer pathway. In CuFc-F, both of the photoexcited copper(I)-complexed and fullerene moieties are quenched by the presence of the ferrocene unit, most likely via ultrafast energy transfer