Emission polypyridine complexes

Room temperature emission has been observed for a number of transition metal complexes. Examples include Rh111 ammines,53 [Pt(CN)4]2-,54 and some Cu1 phosphine complexes.55 An important class is that of the polypyridine complexes of Ru11 and related species.56 This last emission, probably from a 3CT state, is quite strong and its occurrence has made possible a number of detailed studies of electron transfer quenching reactions. 

In dichloromethane solution, the [Ru(bpy)2(l)]2+ complex (Scheme 1) exhibits an absorption band at 455 nm (emax = 10400 M em Figure 5) and an emission band at 619 nm (x = 733 ns, cf> = 0.05, Figure 5, Table 1). These bands can straightforwardly be assigned to spin-allowed and, respectively, spin-forbidden metal-to-ligand-charge-transfer (MLCT) excited states, characteristic of Ru(II) polypyridine complexes[6a,c,e]. 

Prodi examined the photophysical properties of supramolecular assemblies containing polypyridine complexes and pyrene chromophores. Using the complex [(bpy)20s(bpy0bpy)]2+ (Scheme 5) and pyrene-1-carboxylic acid, the authors demonstrated that, upon addition of Zn2+, complex formation occurs in which the Zn2+ links together the free bpy of the Os complex and the carboxyl of the pyrene. Excitation of the Os(II) MLCT absorption results in exclusive emission from the 3MLCT state of the Os complex [84]. 

An assessment of the energy gap, AE, between emissive and 3MC levels can be obtained by studying the temperature dependence of the luminescence properties, as illustrated by several systematic studies for Ru(II)-polypyridine complexes [3,97-107]. This can be done by using an Arrhenius-like expression, Eq. 7 [98]. 

Luminescent ruthenium(II) polypyridine indole complexes such as [Ru (bpy)2(bpy-indole)]2+ (37) and their indole-free counterparts have been synthesised and characterised [77]. The ruthenium(II) indole complexes display typical MLCT (djt(Ru) tt (N N)) absorption bands, and intense and long-lived orange-red 3MLCT (djt(Ru) -> Ti (bpy-indolc)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. In contrast to the rhenium(I) indole complexes, the indole moiety does not quench the emission of the ruthenium(II) polypyridine complexes because the excited complexes are not sufficiently oxidising to initiate electron-transfer reactions. Emission titrations show that the luminescence intensities of the ruthenium(II) indole complexes are only increased by ca. 1.38- to... 

In the following sections, luminescent organometallic rhenium(I) and iridium(III) polypyridine complexes relying on the labelling or binding strategies mentioned above will be described. We focus on the molecular structures, spectroscopic and photophysical properties of the complexes, and the emissive behaviour and potential applications of the labelled bioconjugates. 

Despite the rich emission properties of rhenium(I) polypyridine complexes being well documented, reports on the interactions of related complexes with DNA are limited compared to the ruthenium(II) analogues. The DNA-binding properties of... 

The emission properties of rhenium(I) polypyridine complexes have been utilized in biological studies. Activation of the coordinated isonicotinic acid of the complex [Re(CO)3 (2,9-Mc2-4,7-Ph2-phen)(py-4-COOH)]+... 

Time-resolved, step-scan FT-IR spectroscopy has been used to monitor the v(CO) frequencies of rhenium(I) carbonyl polypyridine complexes and hence to study the excited-state electronic structures of these systems. The MLCT and IT character in the emissive states of [Re(CO)3(phen)(py-4-Me)]+ and [Re(CO)3(dppz)(PPh3)]+, respectively, has been studied by this technique. The presence of two close-lying states of MLCT and IL character for the complex [Re(CO)3(4,4 - NH2 2-bpy)(py-4-Et)]+ was also confirmed. 

Figure 8. Chemiluminescence in redox-catalytic cycles. The metal-polypyridine complex M acts as light-emission sensitizer, LES [74, 266], D and A can be either a chemical reductant and oxidant, respectively, or an electrode polarized at appropriate potential.

Among outputs, luminescence emission is considered to be mie of the most attractive, owing to the ease of detection and the cheap fabrication of devices in which it is detected. Many examples of fluorescent photochromic molecules have been published, by combining a DTE unit with a fluorophore [4]. Incorporation of the DTE fragment into the ligands of transition-metal polypyridine complexes allows the photoreaction to proceed via a triplet state leading to a photoregulation of phosphorescence. 

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