Synthesis and luminescence properties of cyclometalated iridium(III) complexes incorporating conjugated benzotriazole units

The stepwise synthesis of imidazo[4,5-f]-1,10-phenanthroline-based ligands that incorporate conjugated benzotriazole units are described. Corresponding cyclometalated Ir(III) complexes of the type [Ir(CˆN)2(L)]BF4 (where CˆN = cyclometalating ligand; L = phenanthroline type ligand) are reported. The complexes were characterized using a variety of techniques, including IR, NMR, UV-vis. spectroscopies, mass spectrometry and cyclic voltammetry. The [Ir(ppy)2(L)]BF4 complexes display luminescence in the visible region with the benzotriazole variants showing blue shifted emission around 495 nm. Supporting TD-DFT calculations predict that a mixture of MLCT and LLCT character may contribute to the HOMO-LUMO transition of the benzotriazole derivatives

Luminescent 1,8-Naphthalimide-Derived ReI Complexes: syntheses, spectroscopy, X-ray structure and preliminary bioimaging in fission yeast cells

A series of picolyl-functionalised, fluorescent 1,8-naphthalimide ligands (L) have been synthesised and coordi-nated to ReI to form luminescent cationic complexes of the general form fac-[Re(phen)(CO)3(L)]BF4. The complexes were characterised by using a range of spectroscopic and analytical techniques. One example of a complex was also characterised in the solid-state by using single-crystal X-ray diffraction, reveal-ing a distorted octahedral coordination sphere at ReI and Re– C/Re–N bond lengths within the expected ranges. All ligands were shown to be fluorescent, with the 4-amino derivatives showing intramolecular charge transfer in the visible region (511–534 nm). The complexes generally showed a mixture of ligand-centred and/or 3MLCT emission depending upon the na-ture of the coordinated 1,8-naphthalimide ligand. For selected complexes, confocal fluorescence microscopy was undertaken by using fission yeast cells (Schizosaccharomyces pombe) and showed that the structure of the 1,8-naphthalimide ligand influ-ences the uptake and localisation of the rhenium complex

A novel cobalt complex for enhancing amperometric and impedimetric DNA detection

In this work we present a novel cobalt complex, [Co(GA)2(aqphen)]Cl that is water-soluble, redox-active and binds to dsDNA. We report that this complex can be used as a signal enhancer when detecting DNA hybridisation using electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The compound mediates its EIS signal enhancement by causing an increase in charge transfer resistance (Rct) when bound to dsDNA. Increased peak currents are also observed with DPV when the compound is incubated with dsDNA as compared with ssDNA. We believe that this compound intercalates specifically with dsDNA and alters the DNA structure to affect the electrostatic barrier to charged redox markers in solution. To our knowledge this is the first example of a single compound that can enhance both amperometric and impedimetric signals for DNA detection. Our findings enable the development of a label-free and multi-modal approach to improve the sensitivity, accuracy and speed of electrochemical DNA detection

The coordination chemistry of substituted anthraquinones: Developments and applications

Anthraquinone has found diverse use within the sphere of coordination chemistry. The sheer breadth of application in this context has been driven by the remarkable physical and biological properties that are known for a wide variety of anthraquinone derivatives. This review discusses three main areas of research and development: (i) the coordination chemistry of substituted anthraquinones, including self-assembled systems, coordination polymers and metal organic frameworks; (ii) the incorporation of anthraquinone into ligand structures and their resultant chemistry with both d- and f-block metal ions; (iii) the application of metal-anthraquinone species to biological and chemosensing disciplines. Key aspects regarding synthetic approaches and physical characteristics are discussed throughout, with particular attention and focus on the electronic and redox properties of the species in question

ChemInform Abstract: The Coordination Chemistry of Substituted Anthraquinones: Developments and Applications

Anthraquinone has found diverse use within the sphere of coordination chemistry. The sheer breadth of application in this context has been driven by the remarkable physical and biological properties that are known for a wide variety of anthraquinone derivatives. This review discusses three main areas of research and development: (i) the coordination chemistry of substituted anthraquinones, including self-assembled systems, coordination polymers and metal organic frameworks; (ii) the incorporation of anthraquinone into ligand structures and their resultant chemistry with both d- and f-block metal ions; (iii) the application of metal-anthraquinone species to biological and chemosensing disciplines. Key aspects regarding synthetic approaches and physical characteristics are discussed throughout, with particular attention and focus on the electronic and redox properties of the species in question

Fluorescent rhenium-naphthalimide conjugates as cellular imaging agents

A range of biologically compatible, fluorescent rhenium-naphthalimide conjugates, based upon the rhenium fac-tricarbonyl core, has been synthesized. The fluorescent ligands are based upon a N-functionalized, 4-amino-derived 1,8-naphthalimide core and incorporate a dipicolyl amine binding unit to chelate Re(I); the structural variations accord to the nature of the alkylated imide with ethyl ester glycine (L1), 3-propanol (L2), diethylene glycol (L3), and benzyl alcohol (L4) variants. The species are fluorescent in the visible region between 505 and 537 nm through a naphthalimide-localized intramolecular charge transfer, with corresponding fluorescent lifetimes of up to 9.8 ns. The ligands and complexes were investigated for their potential as imaging agents for human osteoarthritic cells and protistan fish parasite Spironucleus vortens using confocal fluorescence microscopy. The results show that the specific nature of the naphthalimide structure serves to control the uptake and intracellular localization of these imaging agents. Significant differences were noted between the free ligands and complexes, with the Re(I) complex of L2 showing hydrogenosomal localization in S. vortens

Using Substituted Cyclometalated Quinoxaline Ligands To Finely Tune the Luminescence Properties of Iridium(III) Complexes

The syntheses of five new heteroleptic iridium complexes <b>[Ir­(L</b>^{<b>1</b>–<b>4</b>}<b>)</b>_<b>2</b><b>(Diobpy)]­PF</b>_<b>6</b> (where Diobpy = 4,4′-dioctylamido-2,2′-bipyridine) and <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(bpy)]­PF</b>_<b>6</b> (where L = <i>para</i>-substituted 2,3-diphenylquinoxaline cyclometalating ligands; bpy = 2,2′-bipyridine) are described. The structures of <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(Diobpy)]­PF</b>_<b>6</b> and <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(bpy)]­PF</b>_<b>6</b> show that the complexes each adopt a distorted octahedral geometry with the expected <i>trans</i>-N, <i>cis</i>-C arrangement of the cyclometalated ligands. Electrochemical studies confirmed subtle perturbation of the Ir^III/IV redox couple as a function of ligand variation. Luminescence studies showed the significant contribution of ³MLCT to the phosphorescent character with predictable and modestly tunable emission wavelengths between 618 and 636 nm. DFT studies provided approximate qualitative descriptions of the HOMO {located over the Ir­(5d) center (11–42%) and the phenylquinoxaline ligand (54–87%)} and LUMO {located over the ancillary bipyridine ligands (ca. 93%)} energy levels of the five complexes, confirming significant MLCT character. TD-DFT calculations indicate that UV–vis absorption and subsequent emission has substantial MLCT character, mixed with LLCT. Predicted absorption and emission wavelengths are in good general agreement with the UV–vis and luminescence experiments

Using Substituted Cyclometalated Quinoxaline Ligands To Finely Tune the Luminescence Properties of Iridium(III) Complexes

The syntheses of five new heteroleptic iridium complexes <b>[Ir­(L</b>^{<b>1</b>–<b>4</b>}<b>)</b>_<b>2</b><b>(Diobpy)]­PF</b>_<b>6</b> (where Diobpy = 4,4′-dioctylamido-2,2′-bipyridine) and <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(bpy)]­PF</b>_<b>6</b> (where L = <i>para</i>-substituted 2,3-diphenylquinoxaline cyclometalating ligands; bpy = 2,2′-bipyridine) are described. The structures of <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(Diobpy)]­PF</b>_<b>6</b> and <b>[Ir­(L</b>^<b>3</b><b>)</b>_<b>2</b><b>(bpy)]­PF</b>_<b>6</b> show that the complexes each adopt a distorted octahedral geometry with the expected <i>trans</i>-N, <i>cis</i>-C arrangement of the cyclometalated ligands. Electrochemical studies confirmed subtle perturbation of the Ir^III/IV redox couple as a function of ligand variation. Luminescence studies showed the significant contribution of ³MLCT to the phosphorescent character with predictable and modestly tunable emission wavelengths between 618 and 636 nm. DFT studies provided approximate qualitative descriptions of the HOMO {located over the Ir­(5d) center (11–42%) and the phenylquinoxaline ligand (54–87%)} and LUMO {located over the ancillary bipyridine ligands (ca. 93%)} energy levels of the five complexes, confirming significant MLCT character. TD-DFT calculations indicate that UV–vis absorption and subsequent emission has substantial MLCT character, mixed with LLCT. Predicted absorption and emission wavelengths are in good general agreement with the UV–vis and luminescence experiments

Alkynyl-naphthalimide Fluorophores: Gold Coordination Chemistry and Cellular Imaging Applications

A range of fluorescent alkynyl-naphthalimide fluorophores has been synthesized and their photophysical properties examined. The fluorescent ligands are based upon a 4-substituted 1,8-naphthalimide core and incorporate structural variations (at the 4-position) to tune the amphiphilic character: chloro (<b>L1</b>), 4-[2-(2-aminoethoxy)­ethanol] (<b>L2</b>), 4-[2-(2-methoxyethoxy)­ethylamino] (<b>L3</b>), piperidine (<b>L4</b>), morpholine (<b>L5</b>), 4-methylpiperidine (<b>L6</b>), and 4-piperidone ethylene ketal (<b>L7</b>) variants. The amino-substituted species (<b>L2</b>–<b>L7</b>) are fluorescent in the visible region at around 517–535 nm through a naphthalimide-localized intramolecular charge transfer (ICT), with appreciable Stokes’ shifts of ca. 6500 cm^–1 and lifetimes up to 10.4 ns. Corresponding two-coordinate Au­(I) complexes [Au­(L)­(PPh₃)] were isolated, with X-ray structural studies revealing the expected coordination mode via the alkyne donor. The Au­(I) complexes retain the visible fluorescence associated with the coordinated alkynyl-naphthalimide ligand. The ligands and complexes were investigated for their cytotoxicity across a range of cell lines (LOVO, MCF-7, A549, PC3, HEK) and their potential as cell imaging agents for HEK (human embryonic kidney) cells and Spironucleus vortens using confocal fluorescence microscopy. The images reveal that these fluorophores are highly compatible with fluorescence microscopy and show some clear intracellular localization patterns that are dependent upon the specific nature of the naphthalimide substituent

Fluorescent Rhenium-Naphthalimide Conjugates as Cellular Imaging Agents

A range of biologically compatible, fluorescent rhenium-naphthalimide conjugates, based upon the rhenium <i>fac</i>-tricarbonyl core, has been synthesized. The fluorescent ligands are based upon a N-functionalized, 4-amino-derived 1,8-naphthalimide core and incorporate a dipicolyl amine binding unit to chelate Re­(I); the structural variations accord to the nature of the alkylated imide with ethyl ester glycine (<b>L</b>^<b>1</b>), 3-propanol (<b>L</b>^<b>2</b>), diethylene glycol (<b>L</b>^<b>3</b>), and benzyl alcohol (<b>L</b>^<b>4</b>) variants. The species are fluorescent in the visible region between 505 and 537 nm through a naphthalimide-localized intramolecular charge transfer, with corresponding fluorescent lifetimes of up to 9.8 ns. The ligands and complexes were investigated for their potential as imaging agents for human osteoarthritic cells and protistan fish parasite <i>Spironucleus vortens</i> using confocal fluorescence microscopy. The results show that the specific nature of the naphthalimide structure serves to control the uptake and intracellular localization of these imaging agents. Significant differences were noted between the free ligands and complexes, with the Re­(I) complex of <b>L</b>^<b>2</b> showing hydrogenosomal localization in <i>S. vortens</i>