Alistair J. Lees

Transition metal based supramolecular systems: synthesis, photophysics, photochemistry and their potential applications as luminescent anion chemosensors

This review describes our recent research results on several transition-metal based supramolecular systems. A number of self-assembly metallocyclophanes and cages have been prepared. We have found that the photophysical properties of these systems are highly dependent on the nature of the bridging ligands and that many of these metallocyclophanes and cages are capable of binding different guest molecules such as inorganic anions and a variety of aromatic compounds. Moreover, trinuclear (diimine) rhenium(I) tricarbonyl complexes linked by a stilbene-like ligand exhibit most interesting photoswitching features, where the luminescence from the complexes can be switched on and off by photoinduced ligand isomerization. In addition, a structurally simple and easily synthesized luminescent anion receptor has been recently developed and it displays outstanding sensitivity and selectivity toward anionic species. We also review the synthesis of two shape-persistent hexagonal phenylacetylenes and their use as ligands to synthesize dinuclear transition-metal complexes. The photophysical properties of both phenylacetylenic ligands and their corresponding metal complexes are summarized.

The Luminescence Rigidochromic Effect Exhibited by Organometallic Complexes: Rationale and Applications.

Several transition-metal organometallic complexes exhibit an especially pronounced hypsochromic shift of their luminescence bands when their solution environment becomes more rigid. This unusual sp...

FT-IR and XPS study of copper(II) complexes of imidazole and benzimidazole

Abstract Several Cu(II) complexes coordinated to imidazole (IMDAH) and benzimidazole (BIMDAH) ligands have been isolated as powdered solids. Compounds prepared are Cu(BIMDAH)4Cl2, Cu(IMDAH)4Cl2, Cu(BIMDAH)2Cl2, Cu(IMDAH)2Cl2 and Cu(BIMDA)2 (BIMDA = deprotonated form of BIMDAH ligand). These compounds have been characterized by elemental analysis, and by diffuse reflectance Fourier Transform and X-ray photoelectron spectroscopy. The results show that Cu(BIMDAH)4Cl2 and Cu(IMDAH)4Cl2 are formed as discrete mononuclear complexes in which the ligands are coordinated in a monodentate fashion. In contrast, the Cu- (BIMDAH)2Cl2 and Cu(IMDAH)2Cl2 complexes are formed as polymeric species. The Cu(BIMDA)2 complex also forms a polymeric structure with the ligands coordinated in a bidentate manner. X-ray photoelectron data illustrates that the surface composition of each of these complexes closely resembles that of the bulk material.

Organometallic complexes as luminescence probes in monitoring thermal and photochemical polymerizations

Abstract This review describes recent developments where several organometallic complexes have been employed as luminescence probes to monitor industrially important thermal and photochemical polymerization reactions. Both epoxy resin and acrylate thin-film materials are discussed. Attention is focused on polymer systems incorporating the metal complexes, W(CO)4L and fac-XRe(CO)3L (X=Cl, Br or I, and L is an α,α′-diimine ligand such as 2,2′-bipyridine or 1,10-phenanthroline, and related derivatives) which are shown to offer considerable promise as spectroscopic probes. A key feature of these organometallic systems is that they are emissive from low-lying metal-to-ligand charge transfer (MLCT) excited states and that these energy levels are sensitive to environmental rigidity. The luminescence properties of these complexes in both solution and polymeric media are examined in detail and the photophysical parameters of the MLCT excited states are correlated with spectroscopic and rheological measurements acquired during the curing process of the polymer.

Anion recognition through hydrogen bonding: a simple, yet highly sensitive, luminescent metal-complex receptor

A new luminescent rhenium(I) polypyridyl-based receptor for a variety of inorganic anions has been designed and synthesized and this artificial receptor shows high affinities for halides, cyanide and acetate anions with binding constants as high as 104–105 M−1 and a detection limit as low as 10−8 M in CH2Cl2 solution.

Photophysics and Photochemistry of Organometallic Rhenium Diimine Complexes

This review describes the photophysics and photochemistry of various diimine rhenium(I) tricarbonyl complexes. The exceptionally diverse photophysical behavior of these complexes is largely dependent on the nature of their lowest excited states. These excited states and the excited-state characteristics can be easily changed by varying the substituents on either the diimine ligands or the ancillary ligands. The prolificacy of the photophysical and photochemical properties of diimine rhenium(I) tricarbonyl complexes allows for a range of important applications such as light- emitting devices, sensors, probes for photo-polymerization, optical switches, nonlinear optical materials, radiopharmaceuticals, carbon dioxide reduction and supramolecular chemistry. We have covered the studies that best characterize the state of the field as far as the most significant fundamental photochemical advances, and the applications of the photochemistry of rhenium complexes.

Photophysics of organometallics

PlatinumII Acetylide Photophysics.- Photophysics and Photochemistry of Organometallic Rhenium Diimine Complexes.- Exploitation of Luminescent Organometallic Rhenium(I) and Iridium(III) Complexes in Biological Studies.- Ultrafast Excited-State Processes in Re(I) Carbonyl-Diimine Complexes: From Excitation to Photochemistry.- Photophysics of CO Loss from Simple Metal Carbonyl Complexes.- Organometallic Pt(II) and Ir(III) Triplet Emitters for OLED Applications and the Role of Spin-Orbit Coupling: A Study Based on High-Resolution Optical Spectroscopy.

Photochemical features of intermolecular C–H bond activation

Abstract The photophysical and photochemical properties of the C–H activating (η5-C5H5)Rh(CO)2, (η5-C5Me5)Rh(CO)2, (η5-C5H5)Ir(CO)2 and (HBPz3*)Rh(CO)2 (Pz*=3,5-dimethylpyrazolyl) complexes in room-temperature hydrocarbon solutions are compared and contrasted. Recent quantitative measurements of the solution photochemistry and kinetic analyses of the reaction pathways are discussed. The data reveal that the C–H and Si–H activation reactions occur via similar photochemical routes, whereas the ligand photosubstitution reaction proceeds by a different pathway. Several key mechanistic features of the light-induced intermolecular C–H bond activation process are identified.

The photochemical reactivity of triosmium cluster complexes containing 2-mercaptopyridine ligands: the crystal and molecular structures of the linked clusters [{Os3H(CO)10}2(μ-SC5H3NCO2)] and [{Os3H(CO)9} (μ-SC5H3NCO2){Os3H(CO)10}]

Abstract The 2-mercaptopyridine triosmium cluster complexes, [{Os 3 H(CO) 10 } 2 (μ-SC 5 H 3 NCO 2 )], [Os 3 H(CO) 10 {SC 5 H N(OH)}] and [Os 3 H(CO) 10 (SC 5 H 4 N)] upon exposure to irradiation at 366 nm undergo photochemical decarbonylation reactions in which the nitrogen of the mercaptopyridine ligand displaces a carbonyl on the third osmium of the thiolate-bridged triangle to yield [{Os 3 H(CO) 10 } 2 (μ-SC 5 H 3 NCO 2 )], [Os 3 H(CO) 9 {SC 5 H 3 N(OH)}] and [Os 3 H(CO) 9 (SC 5 H 4 N)]. The reactions proceed cleanly and quantum yields have been determined. The clusters have been characterised by spectroscopic means and the structures of [{Os 3 H(CO) 10 } 2 (μ-SC 5 H 3 NCO 2 )] and [{Os 3 H(CO) 9 }(μ-SC 5 H 3 NCO 2 ){Os 3 H(CO) 10 }] established by single-crystal X-ray analyses. In both stru osmiums form two triangles, with the carboxylate bridging one edge of one triangle and the sulphur that of a second. For [{Os 3 H(CO) 9 }(μ-SC 5 h 3 NCO 2 ){Os 3 H(CO) 10 }] the nitrogen has displanced a carbonyl from the third somium o thiolate-bridged osmium triangle.

Photophysical aspects of CH bond activation in rhodium dicarbonyl complexes

The solution photochemistry of CH bond activating CpRh(CO)2, Cp∗Rh(CO)2 and (HBPz3∗)Rh(CO)2 complexes (Cp = η5-C5H5; Cp∗ = η5-C5Me5; HBPz3∗ = tris(3,5-dimethylpyrazolyl)borate) has been investigated at several excitation wavelengths. Quantitative photochemical measurements have been obtained for ligand photosubstitution and intermolecular SiH/CH bond activation reactions through a determination of absolute quantum efficiencies. In each complex the results reveal that the photochemistry is extremely wavelength dependent and two low lying ligand field (LF) excited states are implicated in the mechanism. Population of the upper energy LF excited state leads to effective CO dissociation and subsequent SiH/CH bond activation, whereas excitation into the lower energy LF excited state results in inefficient photochemistry. These experimental observations are related to the electronic absorption characteristics of the molecules and are interpreted on a photophysical scheme involving excited states with quite distinct photochemical reactivities.