Design, synthesis and application of luminescent metal tetrazolato complexes in optical imaging

Fundamental investigation into a series of Re(I) tetrazolato complexes as optical imaging agents provided insight into how structural modifications influence their chemical, photophysical and biological properties. Modulation of the complexes through protonation and methylation of the tetrazolato ligand led to improved photophysical performance. Functionalisation at the diimine ligand revealed photophysical output is not appreciably altered. Live cell imaging with the Re(I) complexes showed HeLa cell uptake with perinuclear localisation

Synthesis, photophysical and electrochemical investigation of dinuclear tetrazolato-bridged rhenium complexes

Starting from anionic tetrazole-based ligands, namely 5-(4’-cyanophenyl)tetrazolate and 5-(4’-pyridyl)tetrazolate, mononuclear and dinuclear complexes of fac-[Re(CO)3(phen)]+ (phen = 1,10-phenanthroline) were prepared and characterized. For the mononuclear complexes, regioselective coordination of the metal fragments on the negatively charged tetrazolato ring is exclusively obtained. Coordination to the benzonitrile and pyridine groups was achieved by previous alkylation of the tetrazole ring. Dinuclear complexes were obtained by treatment of the corresponding mononuclear tetrazole-bound complexes with fac-[Re(CO)3(phen)(THF)]+. The second rhenium fragment coordinated either to the pyridine ring or, in the case of the benzonitrile ligand, to the tetrazole ring. The electrochemical properties were probed in an imidazolium ionic liquid, highlighting reduction processes centered on the phen ligand and oxidation processes localized on the metal. The photophysical properties of the complexes are characterized by phosphorescent emission from triplet metal-to-ligand charge transfer excited states, with trends in the lifetime and quantum yield in qualitative agreement with the energy gap law. The two dinuclear complexes show almost superimposable emission profiles: in the 5-(4’-cyanophenyl) tetrazolate-bridged complex, the two metal fragments coordinated to the tetrazole are equivalent and share a positive charge of +1. On the other hand, the photophysical properties of the 5-(4’pyridyl)tetrazolate-bridged dinuclear complex suggest energy transfer between the two metal centers

Rhenium tetrazolato complexes coordinated to thioalkyl-functionalised phenanthroline ligands: Synthesis, photophysical characterisation, and incubation in live HeLa cells

© The Royal Society of Chemistry 2015. Three new complexes of formulation fac-[Re(CO)3(diim)L], where diim is either 1,10-phenanthroline or 1,10-phenanthroline functionalised at position 5 by a thioalkyl chain, and L is either a chloro or aryltetrazolato ancillary ligand, were synthesised and photophysically characterised. The complexes exhibit phosphorescent emission with maxima around 600 nm, originating from triplet metal-to-ligand charge transfer states with partially mixed ligand-to-ligand charge transfer character. The emission is relatively long-lived, within the 200-400 ns range, and with quantum yields of 2-4%. The complexes were trialed as cellular markers in live HeLa cells, along with two previously reported rhenium tetrazolato complexes bound to unsubstituted 1,10-phenanthroline. All five complexes exhibit good cellular uptake and non-specific perinuclear localisation. Upon excitation at 405 nm, the emission from the rhenium complexes could be clearly distinguished from autofluorescence, as demonstrated by spectral detection within the live cells. Four of the complexes did not appear to be toxic, however prolonged excitation could result in membrane blebbing. No major sign of photobleaching was detected upon multiple imaging on the same cell sample

Synthesis and characterisation of heterobimetallic lanthanoid o-based cluster/cages

The synthesis of new mono-and bimetallic lanthanoid cluster compounds is reported. The metal-to metal ratios of tetra-and pentanuclear clusters were determined by energy-dispersive X-ray spectroscopy (EDS). The EDS results show that, for an equal proportion of lanthanide salts introduced, different metal-to-metal ratios are achieved in the clusters. This ratio appears to be dependent on the size and electron density of the metal atoms. Studies realized the best conditions to achieve a 1:1 ratio

Proton-induced reversible modulation of the luminescent output of rhenium(I), iridium(III), and ruthenium(II) tetrazolate complexes

One of the distinct features of metal–tetrazolate complexes is the possibility of performing electrophilic additions onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the use of a simple protonation–deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission output and performance of a series of Re(I)-tetrazolate-based phosphors of the general formulation fac-[Re(N^N)(CO)3L], where N^N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re(I) complexes, a consistent blue shift (Δλmax ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values (4–13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial condition by further treating the protonated Re(I) complex with a base such as triethylamine. Interestingly, the reversible modulation of luminescent features by the same protonation–deprotonation mechanism appears as a quite general characteristic of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal center with a bidentate mode, such as the corresponding Ir(III) cyclometalates [Ir(C^N)2L] and the Ru(II) polypyridyl derivatives [Ru(bpy)2L]+. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions for the Ir(III) complexes, while almost complete quenching is observed in the case of the Ru(II) analogues

Synthesis, Structural, and Photophysical Investigation of Diimine Triscarbonyl Re(I) Tetrazolato Complexes

none11siThe synthesis, structural, and photophysical properties of a novel family of neutral fac-[Re(N∧N)(CO)3(L)] complexes, where N∧N is either 2,20-bipyridine or 1,10-phenanthroline and L is a para functionalized 5-aryltetrazolate [namely, 5-phenyltetrazolate (Tph-), 4-(tetrazolate-5-yl)benzaldehyde (Tbdz- ), 5-(4-acetylphenyl)tetrazolate (Tacy-), and methyl 4-(tetrazolate-5-yl)benzoate (Tmeb-)] are reported. The complexes were prepared by direct addition of the corresponding tetrazolate anion to the acetonitrile solvated fac-[Re(N∧N)(CO)3]þ precursor. NMR data demonstrate that the coordination of the metal fragment is regiospecific at the N2 atom of the tetrazolate ring. These conclusions are also supported by X-ray structural determinations. Photophysical data were obtained in diluted and deaerated dichloromethane solutions displaying broad and structureless profiles with emission maxima ranging from 566 to 578 nm. The absorption profiles indicate the presence of higher energy intraligand (IL) π-π* transitions and lower energies ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT). As the last two transitions are mixed, they are better described as a metal-ligand-to-ligand charge transfer (MLLCT), a result that is also supported by density functional theory (DFT) calculations. The complexes show excited state lifetime values ranging from 102 to 955 ns, with associated quantum yield between 0.012 and 0.099. Compared to the parent neutral chloro or bromo [Re(N∧N)(CO)3X], the complexes show a slightly improved performance because of the π accepting nature of the tetrazolato ligand. The metal-to-ligand backbonding is in fact depleting the Re center of electron density, thus widening the HOMO-LUMO gap and reducing the non-radiative decay mechanism in accordance with the energy gap law. Finally, the electron-withdrawing or donating nature of the substituent on the phenyltetrazolato ligand allows the fine-tuning of the photophysical properties.mixedM. V. Werrett; D. Chartrand; J.D. Gale; G.S. Hanan; J. G. MacLellan; M. Massi; S. Muzzioli; P. Raiteri; B.W. Skelton; M. Silberstein; S. StagniM. V. Werrett; D. Chartrand; J.D. Gale; G.S. Hanan; J. G. MacLellan; M. Massi; S. Muzzioli; P. Raiteri; B.W. Skelton; M. Silberstein; S. Stagn

Proton-Induced Reversible Modulation of the Luminescent Output of Rhenium(I), Iridium(III), and Ruthenium(II) Tetrazolate Complexes

One of the distinct features of metal–tetrazolate complexes is the possibility of performing electrophilic additions onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the use of a simple protonation–deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission output and performance of a series of Re­(I)-tetrazolate-based phosphors of the general formulation <i>fac</i>-[Re­(N^∧N)­(CO)₃L], where N^∧N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re­(I) complexes, a consistent blue shift (Δλ_max ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values (4–13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial condition by further treating the protonated Re­(I) complex with a base such as triethylamine. Interestingly, the reversible modulation of luminescent features by the same protonation–deprotonation mechanism appears as a quite general characteristic of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal center with a bidentate mode, such as the corresponding Ir­(III) cyclometalates [Ir­(C^∧N)₂L] and the Ru­(II) polypyridyl derivatives [Ru­(bpy)₂L]⁺. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions for the Ir­(III) complexes, while almost complete quenching is observed in the case of the Ru­(II) analogues

Proton-Induced Reversible Modulation of the Luminescent Output of Rhenium(I), Iridium(III), and Ruthenium(II) Tetrazolate Complexes

One of the distinct features of metal–tetrazolate complexes is the possibility of performing electrophilic additions onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the use of a simple protonation–deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission output and performance of a series of Re­(I)-tetrazolate-based phosphors of the general formulation <i>fac</i>-[Re­(N^∧N)­(CO)₃L], where N^∧N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re­(I) complexes, a consistent blue shift (Δλ_max ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values (4–13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial condition by further treating the protonated Re­(I) complex with a base such as triethylamine. Interestingly, the reversible modulation of luminescent features by the same protonation–deprotonation mechanism appears as a quite general characteristic of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal center with a bidentate mode, such as the corresponding Ir­(III) cyclometalates [Ir­(C^∧N)₂L] and the Ru­(II) polypyridyl derivatives [Ru­(bpy)₂L]⁺. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions for the Ir­(III) complexes, while almost complete quenching is observed in the case of the Ru­(II) analogues

Synthesis, Photophysical and Electrochemical Investigation of Dinuclear Tetrazolato-Bridged Rhenium Complexes

Starting from anionic tetrazole-based ligands, namely, 5-(4′-cyanophenyl)­tetrazolate and 5-(4′-pyridyl)­tetrazolate, mononuclear and dinuclear complexes of <i>fac</i>-[Re­(CO)₃(phen)]⁺ (phen = 1,10-phenanthroline) were prepared and characterized. For the mononuclear complexes, regioselective coordination of the metal fragments on the negatively charged tetrazolato ring is exclusively obtained. Coordination to the benzonitrile and pyridine groups was achieved by previous alkylation of the tetrazole ring. Dinuclear complexes were obtained by treatment of the corresponding mononuclear tetrazole-bound complexes with <i>fac</i>-[Re­(CO)₃(phen)­(THF)]⁺. The second rhenium fragment coordinated either to the pyridine ring or, in the case of the benzonitrile ligand, to the tetrazole ring. The electrochemical properties were probed in an imidazolium ionic liquid, highlighting reduction processes centered on the phen ligand and oxidation processes localized on the metal. The photophysical properties of the complexes are characterized by phosphorescent emission from triplet metal-to-ligand charge transfer excited states, with trends in the lifetime and quantum yield in qualitative agreement with the energy gap law. The two dinuclear complexes show almost superimposable emission profiles: in the 5-(4′-cyanophenyl)­tetrazolate-bridged complex, the two metal fragments coordinated to the tetrazole are equivalent and share a positive charge of +1. On the other hand, the photophysical properties of the 5-(4′-pyridyl)­tetrazolate-bridged dinuclear complex suggest energy transfer between the two metal centers

Synthesis, Photophysical and Electrochemical Investigation of Dinuclear Tetrazolato-Bridged Rhenium Complexes

Starting from anionic tetrazole-based ligands, namely, 5-(4′-cyanophenyl)­tetrazolate and 5-(4′-pyridyl)­tetrazolate, mononuclear and dinuclear complexes of <i>fac</i>-[Re­(CO)₃(phen)]⁺ (phen = 1,10-phenanthroline) were prepared and characterized. For the mononuclear complexes, regioselective coordination of the metal fragments on the negatively charged tetrazolato ring is exclusively obtained. Coordination to the benzonitrile and pyridine groups was achieved by previous alkylation of the tetrazole ring. Dinuclear complexes were obtained by treatment of the corresponding mononuclear tetrazole-bound complexes with <i>fac</i>-[Re­(CO)₃(phen)­(THF)]⁺. The second rhenium fragment coordinated either to the pyridine ring or, in the case of the benzonitrile ligand, to the tetrazole ring. The electrochemical properties were probed in an imidazolium ionic liquid, highlighting reduction processes centered on the phen ligand and oxidation processes localized on the metal. The photophysical properties of the complexes are characterized by phosphorescent emission from triplet metal-to-ligand charge transfer excited states, with trends in the lifetime and quantum yield in qualitative agreement with the energy gap law. The two dinuclear complexes show almost superimposable emission profiles: in the 5-(4′-cyanophenyl)­tetrazolate-bridged complex, the two metal fragments coordinated to the tetrazole are equivalent and share a positive charge of +1. On the other hand, the photophysical properties of the 5-(4′-pyridyl)­tetrazolate-bridged dinuclear complex suggest energy transfer between the two metal centers