Luminescent Rhenium Research Articles

Luminescent Rhenium(I) Polypyridine Fluorous Complexes as Novel Trifunctional Biological Probes

We present the synthesis, characterization, and photophysical properties of three luminescent rhenium(I) polypyridine fluorous complexes [Re(Me(2)bpy)(CO)(3)(L)](PF(6)) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine; L = 3-amino-5-(N-((3-perfluorooctyl)propyl)aminocarbonyl)pyridine (py-Rf-NH(2)) (1), 3-isothiocyanato-5-(N-((3-perfluorooctyl)propyl)aminocarbonyl)pyridine (py-Rf-NCS) (2), 3-ethylthioureidyl-5-(N-((3-perfluorooctyl)propyl)aminocarbonyl)pyridine (py-Rf-TU-C(2)H(5)) (3)). The isothiocyanate complex 2 has been used to label bovine serum albumin (BSA) and glutathione (GSH). The photophysical properties of the resultant bioconjugates have been studied. The isolation of the luminescent fluorous rhenium-GSH conjugate from a mixture of 20 amino acids has been demonstrated using fluorous solid-phase extraction (FSPE). Additionally, the cytotoxicity of complexes 1 and 3 toward HeLa cells has been examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cellular uptake properties of complex 3 have also been investigated by laser-scanning confocal microscopy.

Recent Exploitation of Luminescent Rhenium(I) Tricarbonyl Polypyridine Complexes as Biomolecular and Cellular Probes (Eur. J. Inorg. Chem. 24/2011)

AbstractThe cover picture shows the numerous opportunities luminescent rhenium(I) tricarbonyl polypyridine complexes offer regarding the development of probes for biological applications. Since the spectroscopic and luminescence properties of rhenium(I) tricarbonyl polypyridine complexes were reported in the 1970s, a number of sensors and probes have been derived from these complexes. K. K.‐W. Lo et al. describe in their Microreview on p. 3551 ff the fundamental emission characteristics of these complexes and explain why they hold promise for use as luminescent sensors. Additionally, the recent design of rhenium(I) tricarbonyl polypyridine complexes as biomolecular and cellular probes is summarized. Emphasis is placed on the structure–property relationships, bioconjugation, biomolecular binding, cellular uptake, cytotoxicity, and bioimaging studies of these complexes. Mr. Michael Wai‐Lun Chiang is acknowledged for the cover picture design.

Graphical Abstract: Eur. J. Inorg. Chem. 24/2011

AbstractThe cover picture shows the numerous opportunities luminescent rhenium(I) tricarbonyl polypyridine complexes offer regarding the development of probes for biological applications. Since the spectroscopic and luminescence properties of rhenium(I) tricarbonyl polypyridine complexes were reported in the 1970s, a number of sensors and probes have been derived from these complexes. K. K.‐W. Lo et al. describe in their Microreview on p. 3551 ff the fundamental emission characteristics of these complexes and explain why they hold promise for use as luminescent sensors. Additionally, the recent design of rhenium(I) tricarbonyl polypyridine complexes as biomolecular and cellular probes is summarized. Emphasis is placed on the structure–property relationships, bioconjugation, biomolecular binding, cellular uptake, cytotoxicity, and bioimaging studies of these complexes. Mr. Michael Wai‐Lun Chiang is acknowledged for the cover picture design.

Recent Exploitation of Luminescent Rhenium(I) Tricarbonyl Polypyridine Complexes as Biomolecular and Cellular Probes

AbstractThe interesting emission properties of rhenium(I) tricarbonyl polypyridine complexes have been exploited in the development of various sensors and probes for analytes. Luminescent probes targeting biomolecules have also been developed. Additionally, there has been a fast‐growing interest in the cellular uptake properties of these complexes with a focus on their potential as cellular imaging reagents. In this Microreview, we describe the fundamental emission characteristics of luminescent rhenium(I) tricarbonyl polypyridine complexes and explain why they hold promise for use as luminescent sensors. Additionally, we summarize the recent design of these complexes as biomolecular and cellular probes, with an emphasis on studies of their structure–property relationships, bioconjugation, biomolecular binding, cellular uptake, cytotoxicity, and bioimaging applications.

Cover Picture: Luminescent Rhenium(I) Polypyridine Complexes Appended with an α-D-Glucose Moiety as Novel Biomolecular and Cellular Probes (Chem. Eur. J. 30/2011)

Cover Picture: Luminescent Rhenium(I) Polypyridine Complexes Appended with an α-D-Glucose Moiety as Novel Biomolecular and Cellular Probes (Chem. Eur. J. 30/2011)

Luminescent Rhenium(I) Polypyridine Complexes Appended with an α‐D‐Glucose Moiety as Novel Biomolecular and Cellular Probes

Glowing sweets! Three luminescent rhenium(I) polypyridine complexes have been modified with an α-D-glucose moiety. Their biomolecular binding, bacterial staining, and cellular-uptake properties have been examined (see figure). Various experimental results have indicated that glucose transporters play a very important role in the cellular uptake of these glucose complexes.

A DFT exploration of luminescent rhenium(I) tricarbonyl diimine complex with a triarylboron moiety and its F derivative

The geometry, electronic structure, and spectroscopic properties together with the fluoride binding nature of the luminescent rhenium(I) tricarbonyl diimine complex with a triarylboron moiety, [(arB)Re(CO)3(phen)] were investigated by density functional theory (DFT) approach, where, arB = (2,3,5,6-tetramethyl-4-ethynyl-benzene) 3B, phen = 1,10-phenanthroline), The simulated UV–vis absorptions by M06 functional are in excellent agreement with the experimental results. All absorptions are attributed to intra-ligand charge-transfer (ILCT) within the triarylboron ligand but being disturbed by some contribution of metal-to-arylboron ligand charge-transfer (MLCT) characters. Moreover, the 676 nm phosphorescence computed by TPSSh functional originates from the 3LLCT/ 3LMCT transition. Binding the F − results in the re-configuration of the molecular geometry and the variation of the optical properties. The highest energy absorption band is intensified while the lower energy absorption bands are weakened and blue-shifted slightly. The emission maximum is red-shifted to 875 nm after binding the F −.

Protein binding studies of luminescent rhenium(I) diimine complexes

Interaction of four luminescent rhenium(I) diimine complexes, [Re(CO)3(N–N)L]PF6 ((N–N=2,2-bipyridine, L=py-3-COOH) 1a, (N–N=2,2-bipyridine, L=py-3-CONH2) 1b, (N–N=1,10-phenanthroline, L=py-3-COOH) 2a, (N–N=1,10-phenanthroline, L=py-3-CONH2) 2b with bovine serum albumin (BSA) at physiological pH has been examined using UV–Vis absorption and luminescence spectroscopy, excited state lifetime measurement and circular dichroism (CD). In the presence of BSA, the luminescence of Re(I) complexes is quenched due to the locking-in of the probe into the protein environment. Interestingly the probe is released from the protein environment in the presence of sodium dodecyl sulfate (SDS) resulting in the restoration of the original luminescence along with a red shift in the emission maximum. These observations are explained in terms of binding constants (Ka) of probe with protein and surfactant and the nature of the binding has been investigated from Scatchard plot and Hill’s coefficient (n) value. These studies point out that the interaction between Re(I) complexes and BSA is cooperative in nature.

Luminescent rhenium(i) complexes with acetylamino- and trifluoroacetylamino-containing phenanthroline ligands: Anion-sensing study

A series of rhenium complexes with acetylamino- and trifluoroacetylamino-containing 1,10-phenanthroline ligands have been synthesized, characterized and their photophysical and electrochemical properties studied. These complexes were found to show significant UV-vis and emission changes on addition of CN(-), F(-) and AcO(-) anions. Their reactivity towards CN(-), F(-) and AcO(-) anions, was also investigated by UV-vis, emission and (1)H NMR spectroscopy. The reaction product between the trifluoroacetylamino-containing 1,10-phenanthroline ligand and the CN(-) anion has also been structurally characterized by X-ray crystallography.

Synthesis and characterisation of luminescent rhenium tricarbonyl complexes with axially coordinated 1,2,3-triazole ligands

A series of 1-alkyl-4-aryl-1,2,3-triazoles (1-methyl-4-phenyl-1,2,3-triazole (1a); 1-propyl-4-phenyl-1,2,3-triazole (1b); 1-benzyl-4-phenyl-1,2,3-triazole (1c); 1-propyl-4-p-tolyl-1,2,3-triazole (1d)) have been prepared through a one-pot procedure involving in situ generation of the alkyl azide from a halide precursor followed by copper catalysed alkyne/azide cycloaddition (CuAAC) with the appropriate aryl alkyne. Cationic Re(I) complexes [Re(bpy)(CO)(3)(1a-d)]PF(6) (2a-d) were then prepared by stirring [Re(bpy)(CO)(3)Cl] with AgPF(6) in dichloromethane in the presence of ligands 1a-d. X-ray crystal structures were obtained for 2a and 2b. In the solid state, 2a adopts a highly distorted geometry, which is not seen for 2b, in which the plane of the triazole ligand tilts by 13° with respect to the Re-N bond as a result of a π-stacking interaction between the Ph substituent and one of the rings of the bpy ligand. This π-stacking interaction also results in severe twisting of the bpy ligand. Infrared spectra of 2a-d exhibit ν(CO) bands at ∼2035 and ∼1926 cm(-1) suggesting that these ligands are marginally better donors than pyridine (ν(CO) = 2037, 1932 cm(-1)). The complexes are luminescent in aerated dichloromethane at room temperature with emission maxima at 542 to 552 nm comparable to that of the pyridine analogue (549 nm) and blue shifted relative to the parent chloride complex. Long luminescent lifetimes are observed for the triazole complexes (475 to 513 ns) in aerated dichloromethane solutions at room temperature.

Tricarbonyl ReI Complexes from Functionalised Pyridine–Triazole Derivatives: From Mononuclear to Unexpected Dimeric Complexes

AbstractAs a variation of the commonly used bipy ligand in Re(CO)3 chemistry, a series of structurally related complexes in which bipy is replaced by pyridine–triazole ligands (or pyta) bearing a pendant acetyl group on the triazole ring were prepared efficiently by the click chemistry approach. Depending on the nature of the pendant arm, different ReI complexes were obtained. Surprisingly, starting from the ligand with unprotected acetyl group yielded two structural isomers of Re(CO)3 dimeric species. One isomer (compound 5a) was isolated and characterised by X‐ray crystallography. The rhenium atoms are octahedrally coordinated to three carbonyl groups in fac arrangement and to two nitrogen atoms of one pyta and an oxygen atom of the other. DFT calculations confirmed that the isolated isomer represents the thermodynamically favoured form. As expected, these complexes exhibited luminescence. To conclude, the unexpected formation of 5 represents an original strategy toward the synthesis of new luminescent rhenium(I) dimeric (multimeric) species.

Correction to Synthesis and Characterization of Luminescent Rhenium(I) Tricarbonyl Diimine Complexes with a Triarylboron Moiety and the Study of Their Fluoride Ion-Binding Properties

Correction to Synthesis and Characterization of Luminescent Rhenium(I) Tricarbonyl Diimine Complexes with a Triarylboron Moiety and the Study of Their Fluoride Ion-Binding Properties

Synthesis and Characterization of Luminescent Rhenium(I) Tricarbonyl Diimine Complexes with a Triarylboron Moiety and the Study of Their Fluoride Ion-Binding Properties

A series of alkynylrhenium(I) tricarbonyl diimine complexes with a triarylboron moiety has been synthesized and characterized. The binding properties of the complex toward fluoride ions have been studied using electronic absorption and emission spectroscopy and were further supported by (19)F NMR binding experiments.

Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent Devices

AbstractA series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(µ‐Cl)2(CO)6(µ‐1,2‐diazine)], contain diazines bearing alkyl groups in one or in both the β positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time‐dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (ϕ = 0.18–0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77 K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest‐performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer‐based light‐emitting device, with poly(9‐vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7‐bis(diphenylphosphine oxide)‐9‐(9‐phenylcarbazol‐3‐yl)‐9‐phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes.

Electroluminescence: (Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent Devices) Adv. Funct. Mater. 16/2009

Neutral, dinuclear, highly luminescent rhenium(I) complexes are prepared and their photophysical and electrochemical properties investigated by Professor Luisa De Cola and co-workers. For the first time, electroluminescent devices, using a rhenium complex as dopant, obtained by sublimation and by solution processing are described.

Synthesis, Characterization, Ion-Binding Properties, and Fluorescence Resonance Energy Transfer Behavior of Rhenium(I) Complexes Containing a Coumarin-Appended 2,2′-Bipyridine

A series of luminescent rhenium(I) complexes of 2,2′-bipyridine appended with a coumarin fluorophore has been successfully synthesized and characterized. Their photophysical behavior, ion-binding properties, and fluorescence resonance energy transfer (FRET) behavior from the coumarin donor to the rhenium(I) bipyridyl acceptor were studied. The FRET efficiencies were found to vary upon addition of various metal ions with different sizes due to conformational changes. Their stability constants have been determined by both UV−visible and luminescence spectrophotometric methods.

A luminescent rhenium(I) complex of 2,7-dimethyl-1,8-naphthyridine: synthesis, spectroscopy and X-ray crystal structure

2,7-Dimethyl-1,8-naphthyridine (L1) reacts with pentacarbonylchlororhenium in toluene or chloroform to give the target complex fac-{ReCl(CO)3(L1)}. X-ray crystallographic data were obtained for fac-{ReCl(CO)3(L1)}. The structural and 1H NMR data suggest that the ligand coordinates to the rhenium in a bidentate fashion in both solid and solution states. The complex was also found to be luminescent in both solution and solid states. The fluxionality of the ligand in solution causes ligand-centred emission to be observed in solution, whereas only 3MLCT emission was observed in the solid state. Although the complex was air-stable, the lability of L1 was studied in 1H NMR experiments where CD3OD induced complete ligand dissociation over the course of 24 h, and also in reaction of fac-{ReCl(CO)3(L1)} with one equivalent of 2,2′-bipyridine in chloroform which resulted in quantitative ligand exchange.

Reactivity of Electrochemically Generated Rhenium (II) Tricarbonyl α-Diimine Complexes: A Reinvestigation of the Oxidation of Luminescent Re(CO)3(α-Diimine)Cl and Related Compounds

The oxidative electrochemistry of luminescent rhenium (I) complexes of the type Re(CO) 3(LL)Cl, 1, and Re(CO) 3(LL)Br, 2, where LL is an alpha-diimine, was re-examined in acetonitrile. These compounds undergo metal-based one-electron oxidations, the products of which undergo rapid chemical reaction. Cyclic voltammetry results imply that the electrogenerated rhenium (II) species 1 ( + ) and 2 ( + ) disproportionate, yielding [Re(CO) 3(LL)(CH 3CN)] (+), 7, and additional products. Double potential step chronocoulometry experiments confirm that 1 ( + ) and 2 ( + ) react via second-order processes and, furthermore, indicate that the rate of disproportionation is influenced by the basicity and steric requirements of the alpha-diimine ligands. The simultaneous generation of rhenium (I) and (III) carbonyl products was detected upon the bulk oxidation of 1 using infrared spectroelectrochemistry. The rhenium (III) products are assigned as [Re(CO) 3(LL)Cl 2] (+), 5; an inner-sphere electron-transfer mechanism of the disproportionation is proposed on the basis of the apparent chloride transfer. Chemically irreversible two-electron reduction of 5 yields 1 and Cl (-). No direct spectroscopic evidence was obtained for the generation of rhenium (III) tricarbonyl bromide disproportionation products, [Re(CO) 3(LL)Br 2] (+), 6; this is attributed to their relatively rapid decomposition to 7 and dibromine. In addition, the 17-electron radical cations, 7 ( + ), were successfully characterized using infrared spectroelectrochemistry.

A New Class of Isocyanide-Containing Rhenium(I) Bipyridyl Luminophore with Readily Tunable and Highly Environmentally Sensitive Excited-State Properties

A new class of readily tunable and highly environmentally sensitive luminescent rhenium(I) tetra(isocyano)bipyridyl complexes has been synthesized and characterized, and their luminescent properties have been investigated. Preliminary studies showed that the metal-to-ligand charge-transfer [dpi(Re) --> pi*(bpy)] absorption and emission are extremely sensitive to the nature of the solvent and the rigidity of the environment.

Energy transfer from rhenium(i) complexes to covalently attached anthracenes and phenanthrenes

The synthesis and photophysical properties of a series of chromophore-quencher complexes are reported. They are all comprised of a luminescent rhenium(I) tricarbonyl diimine complex that is covalently attached to anthracene or phenanthrene moieties via rigid rod-like p-xylene bridges of variable lengths. Rhenium-to-anthracene energy transfer is strongly exergonic (-DeltaG0 approximately 0.9 eV) and causes very efficient rhenium MLCT luminescence quenching. By contrast, rhenium-to-phenanthrene energy transfer is only observed when complexes with sufficiently high MLCT energies are used because for these dyads, the driving force for energy transfer is low (-DeltaG0 approximately 0.1 eV). For a approximately 15 angstroms donor-acceptor distance, the rate constants of the weakly and the strongly exergonic energy transfer processes differ by more than 3 orders of magnitude.