Accessing unsymmetrical Ru(II) bipyridine complexes: a versatile synthetic mechanism for fine tuning photophysical properties.

Three novel unsymmetrical Ru(II) bipyridine complexes were generated via a convenient, modular, convergent synthetic route. An investigation of their photophysical properties revealed solvent-dependent excited state behaviour including altered absorption and emission wavelengths, emission lifetimes and quantum yields of phosphorescence.

Ru(ii) and Ir(iii) phenanthroline-based photosensitisers bearing o-carborane: PDT agents with boron carriers for potential BNCT.

Four novel transition metal-carborane photosensitisers were prepared by Sonogashira cross-coupling of 1-(4-ethynylbenzyl)-2-methyl-o-carborane (A-CB) with halogenated Ru(ii)- or Ir(iii)-phenanthroline complexes. The resulting boron-rich complexes with one (RuCB and IrCB) or two carborane cages (RuCB2 and IrCB2) were spectroscopically characterised, and their photophysical properties investigated. RuCB displayed the most attractive photophysical properties in solution (λem 635 nm, τT 2.53 µs, and φp 20.4%). Nanosecond time-resolved transient absorption studies were used to explore the 3MLCT nature of the triplet excited states, and the highest singlet oxygen quantum yields (ΦΔ) were obtained for the mono-carborane-phenanthroline complexes (RuCB: 52% and IrCB: 25%). None of the complexes produce dark toxicity in SKBR-3 cells after incubation under photodynamic therapy (PDT) conditions. Remarkably, mono-carboranes RuCB and IrCB were the best internalised by the SKBR-3 cells, demonstrating the first examples of tris-bidentate transition metal-carborane complexes acting as triplet photosensitisers for PDT with a high photoactivity; RuCB or IrCB killed ∼50% of SKBR-3 cells at 10 µM after irradiation. Therefore, the high-boron content and the photoactive properties of these photosensitisers make them potential candidates as dual anti-cancer agents for PDT and Boron Neutron Capture Therapy (BNCT).

Multinuclear Ru(ii) and Ir(iii) decorated tetraphenylporphyrins as efficient PDT agents.

Two novel porphyrin-core systems were prepared by Sonogashira cross-coupling of the terminal alkyne groups of meso-tetra(4-ethynylphenyl)porphyrin-Zn(ii) (P-1) with halogenated Ru(ii)- or Ir(iii)-phenanthroline complexes. The resulting compounds (P-Ru and P-Ir) were spectroscopically characterised and their photophysical properties were investigated (λem 625, 665 nm; τT 339.6 µs (P-Ru) and λem 530, 612, 664 nm; τT 396.6 µs (P-Ir)). Nanosecond time-resolved transient absorption studies were used to explore the 3MLCT nature of the triplet excited states, and the singlet oxygen quantum yields were determined (ΦΔ 44.8 (P-Ru), 33.2 (P-Ir)%). The subcellular uptake of P-Ru and P-Ir and their application as photosensitisers (PS) in photodynamic therapy (PDT) were explored due to their solution photophysics and absence of dark toxicity. Upon irradiation (λexc = 620-630 nm; 10 min; 33 J cm-2), both P-Ru and P-Ir killed 90% of SKBR-3 cells at 1 µM. Notably P-Ru induced a 77% decrease in cell viability at only 0.25 µM.

Chemistry of 4-[(4-bromophenyl)ethynyl]pyridine at metal surfaces studied by STM.

Molecular architectures (Kagome networks, coordinated/covalent dimers and branched coordination chains) via self-assembly, Ullmann reaction and pyridine coordination of 4-[(4-bromophenyl)ethynyl]pyridine are found to be sensitive to the underlying metallic surfaces. The molecular species were characterised on the surface by low-temperature scanning tunnelling microscopy (LT-STM) at sub-molecular level.

Novel ruthenium and iridium complexes of N-substituted carbazole as triplet photosensitisers.

Novel mono- and di-nuclear Ru(ii) and Ir(iii) complexes, bearing a modified carbazole moiety are synthesised. In comparison to their mononuclear analogues, the homonuclear diatomic complexes (RuCRu and IrCIr), in which the carbazole containing-ligand functions as a bridge, display increased absorbance in the visible region, and give rise to higher singlet oxygen quantum yields.

Iridium(III) Complexes Bearing Pyrene-Functionalized 1,10-Phenanthroline Ligands as Highly Efficient Sensitizers for Triplet-Triplet Annihilation Upconversion.

"Chemistry-on-the-complex" synthetic methods have allowed the selective addition of 1-ethynylpyrene appendages to the 3-, 5-, 3,8- and 5,6-positions of IrIII -coordinated 1,10-phenanthroline via Sonogashira cross-coupling. The resulting suite of complexes has given rise to the first rationalization of their absorption and emission properties as a function of the number and position of the pyrene moieties. Strong absorption in the visible region (e.g. 3,8-substituted Ir-3: λabs =481 nm, ϵ=52 400 m-1 cm-1 ) and long-lived triplet excited states (e.g. 5-substituted Ir-2: τT =367.7 µs) were observed for the complexes in deaerated CH2 Cl2 . On testing the series as triplet sensitizers for triplet-triplet annihilation upconversion, those IrIII complexes bearing pyrenyl appendages at the 3- and 3,8-positions (Ir-1, Ir-3) were found to give optimal upconversion quantum yields (30.2 % and 31.6 % respectively).

Sonogashira Cross-Coupling as a Route to Tunable Hybrid Organic-Inorganic Rods with a Polyoxometalate Backbone.

A new diiodo-bifunctionalized Anderson-Evans polyoxometalate (TBA)3[MnMo6O18{(OCH2)3CNHCO(C6H4-p-I)}2] (1; TBA = [(C4H9)4N]+) was prepared and used as a new platform to generate tunable rigid-molecular rods (2a-2c) via Sonogashira cross-coupling. Single-crystal X-ray diffraction analysis of 1 and 2c reveals that they are type B Anderson-Evans structures with molecular lengths of 23 and 38 Å, respectively.

Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of Ir(III) Complexes containing Extended Phenanthrolines.

A series of Ir(III) complexes, based on 1,10-phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross-coupling reactions using a "chemistry-on-the-complex" method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light-harvesting group. Intense UV/Vis absorption was observed for the Ir(III) complexes with two light-harvesting groups at the 3- and 8-positions of the phenanthroline. The asymmetric Ir(III) complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature (77 K) and nanosecond time-resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet-oxygen ((1) O2 ) sensitization and triplet-triplet annihilation (TTA)-based upconversion were explored. Highly efficient TTA upconversion (ΦUC =28.1 %) and (1) O2 sensitization (ΦΔ =97.0 %) were achieved for the asymmetric Ir(III) complex, which showed intense absorption in the visible region (λabs =482 nm, ϵ=50900 m(-1) cm(-1) ) and had a long-lived triplet excited state (53.3 µs at RT).

One-Pot, High-Yielding, Oxidative Cyclodehydrogenation Route for N-Doped Nanographene Synthesis.

An intramolecular oxidative cyclodehydrogenation via a one-pot process is described, which induces selective C-C bond formation and bromine functionalization. The application of this new route gives rise to a novel family of partially fused, selectively brominated N-doped pyrimidine graphenes.

Methoxy functionalisation: exerting synthetic control of the supramolecular and electronic structure of nitrogen-doped nanographenes.

We describe a series of functionalized N-containing heterosuperbenzenes, created with a view to investigating the strategic role of methoxy substituents in (i) promoting cyclodehydrogenation and (ii) tuning the electronic properties and (iii) the supramolecular order in the resultant fused products.

Intriguing Diels-Alder products: chiral centres with an added twist.

Two chiral fluoranthene-based polyaromatics were isolated from a Diels-Alder cycloaddition between two molecules of 7,9-diphenylcyclopenta[a]acenapthylene-8-one. The two highly coloured, novel compounds were characterized by a combination of spectroscopic techniques and single crystal X-ray diffraction. Structural differences between the unexpected products included the nature of their conjugated fluoranthene portions and the position, strain and handedness of their chiral centres.

Structure-property relationships and (1)O)2) photosensitisation in sterically encumbered diimine Pt(II) acetylide complexes.

A series of sterically encumbered [Pt(L)(σ-acetylide)2 ] complexes were prepared in which L, a dendritic polyaromatic diimine ligand, was held constant (L=1-(2,2'-bipyrid-6-yl)-2,3,4,5-tetrakis(4-tert-butylphenyl)benzene) and the cis ethynyl co-ligands were varied. The optical properties of the complexes were tuned by changing the electronic character, extent of π conjugation and steric bulk of the ethynyl ligands. Replacing electron-withdrawing phenyl-CF3 substituents (4) with electron-donating pyrenes (5) resulted in a red shift of both the lowest-energy absorption (ΔE=3300 cm(-1) , 61 nm) and emission bands (ΔE=1930 cm(-1) , 64 nm). The emission, assigned in each case as phosphorescence on the basis of the excited-state lifetimes, switched from being (3) MMLL'CT-derived (mixed metal-ligand-to-ligand charge transfer) when phenyl/polyphenylene substituents (3, 4, 6) were present, to ligand-centred (3) ππ* when the substituents were more conjugated aromatic platforms [pyrene (5) or hexa-peri-hexabenzocoronene (7)]. The novel Pt(II) acetylide complexes 5 and 7 absorb strongly in the visible region of the electromagnetic spectrum, which along with their long triplet excited-state lifetimes suggested they would be good candidates for use as singlet-oxygen photosensitisers. Determined by in situ photooxidation of 1,5-dihydroxynaphthalene (DHN), the photooxidation rate with pyrenyl-5 as sensitiser (kobs =39.3×10(-3)  min(-1) ) was over half that of the known (1) O2 sensitiser tetraphenylporphyrin (kobs =78.6×10(-3)  min(-1) ) under the same conditions. Measured (1) O2 quantum yields of complexes 5 and 7 were half and one-third, respectively, of that of TPP, and thus reveal an efficient triplet-triplet energy-transfer process in both cases.

Visible light-harvesting trans bis(alkylphosphine) platinum(II)-alkynyl complexes showing long-lived triplet excited states as triplet photosensitizers for triplet-triplet annihilation upconversion.

Symmetric and asymmetric linear trans-bis(tributylphosphine) Pt(II) bis(acetylide) complexes with functionalized aryl alkynyl ligands (coumarin, naphthalimide and phenyl acetylides) were prepared, which show enhanced absorption in the visible region (molar absorption coefficients up to 76,800 M(-1) cm(-1) at 459 nm) and long-lived triplet excited states (up to 139.9 µs). At room temperature, the naphthalimide acetylide-phenyl acetylide complex (Pt-4) shows dual emission (fluorescence-phosphorescence), whereas other complexes show only fluorescence emission. The triplet excited states of the complexes were studied with nanosecond time-resolved transient difference absorption spectroscopy and DFT calculations on the spin density surface. The complexes were used as triplet photosensitizers for ratiometric O2 sensing, as well as triplet-triplet annihilation (TTA) upconversion (upconversion quantum yield up to 27.2%). The TTA upconversion of the complexes requires triplet acceptors with different T1 state energy levels and was studied with nanosecond time-resolved emission spectroscopy. Our results are useful for designing new Pt(II) complexes that show strong absorption of visible light and long-lived triplet excited states, as well as for the application of these complexes as triplet photosensitizers for O2 sensing, photocatalysis and TTA upconversion.

The synthesis and characterisation of novel ferrocenyl polyphenylenes.

This work describes the synthesis and characterisation of a new series of polyphenylenes with up to four ferrocenyl moieties. The synthetic route involves the preparation of a number of novel precursors. Cyclopentadienones, generated from the two-fold Knoevenagel condensation of di-ferrocenyl propanones and diketones, are used in [2 + 4] Diels-Alder cycloadditions with appropriately substituted acetylenes. 13 is amongst the compounds isolated. It is the largest ferrocenyl-supported polyaromatic hydrocarbon (PAH) to date. Prepared via a Sonogashira cross-coupling reaction between ethynyl-Fc and iodo-HBC, it comprises a hexa-peri-hexabenzocoronene (HBC) core linked via acetylene to a ferrocenyl unit (Fc). The electrochemical and absorption properties of the ferrocenyl-polyphenylenes and the fully conjugated 13 are discussed. The NLO data for 13, determined by hyper Rayleigh scattering techniques, are compared to those of similar fulleryl-based compounds in the literature.

Terpyridine-fused polyaromatic hydrocarbons generated via cyclodehydrogenation and used as ligands in Ru(II) complexes.

A series of novel fused 4'-substituted 2,2' : 6',2''-terpyridine ligands and their ruthenium(II) complexes were prepared. The unusual 4'-substituents comprised 2,3,4,5-pentaphenylbenzene and its tert-butyl derivative (1 and 2) and the products from oxidative cyclodehydrogenation, i.e. polyaromatic fragments consisting of ten or thirteen fused benzene rings (3 and 4). The syntheses of all the ligands are discussed in terms of the demands and limitations of the Scholl reaction. The optical properties of the ligands, along with the single-crystal X-ray structures of 1 and 2, are presented. The latter show that the pentaphenylbenzene and terpyridine appendages of 1 and 2 are perpendicular in the solid state. Despite the inclusion of the large organic chromophore the absorption and emission properties of the Ru(II) bis-terpy complexes (of ligands 1, 2 and 3) were found to be comparable to those of [Ru(terpy)(2)](2+). They are non-emissive at room temperature but emit at 77 K with excited state lifetimes of 11-12 µs.

Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(II) complexes.

This article reports the preparation of a range of phenyl, pyridyl and pyrazinyl substituted pyridazines via the inverse electron demand [2 + 4] Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazines (bptz) and 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazines (bpztz) and suitable dienophiles including acenaphthalene. The resulting polyaromatic compounds vary systematically in the number of aromatic substituents and the number and position of N-heteroatoms. For four of these compounds, the effect of the molecular changes on the solid-state structures were investigated using single crystal X-ray crystallography. The pyridazines were used as bidentate ligands in {M(II)(bipy)(2)} and tris(homoleptic) complexes (M = Fe, Ru). The optical and electrochemical properties of these complexes reflect the electron accepting character of the new ligands. The facial and meridional isomers of the tris complexes could be separated by column chromatography (on silica), thus allowing a spectral comparison of their absorption and emission properties. The solid-state structures of several of the metal complexes are discussed, including that of the facial isomer of the tris Ru(II) complex of 3,6-bis(2-pyridyl)-4,5-bis(4-pyridyl)pyridazine--a potential preformed geometric motif for the predirected construction of supramolecular assemblies.

A dinuclear extension to constrained heteroleptic Cu(I) systems.

This article reports the synthesis and optical properties of three dinuclear, cationic copper complexes [Cu(2)(µ-dppm)(2)(µ-L)](NO(3))(2) (dppm diphenyldiphosphinomethane, L: L(A) 3,6-bis(2-pyridyl)-4,5-diphenyl-pyridazine, L(B) 3,6-bis(2-pyridyl)-4,5-di(4-pyridyl)-pyridazine and L(C) 3,6-bis(2-pyridyl)-8,9-diazafluoranthene). These were formed on the reaction of [Cu(µ-dppm)(NO(3))](2) with a series of N-donor (bppn) ligands L. The single crystal X-ray structures of [Cu(2)(µ-dppm)(2)(µ-L)](NO(3))(2)·CH(2)Cl(2) were determined and revealed that in both, the two copper atoms are held by three bridging ligands, two dppm ligands and one bppn ligand acting as a tetradentate bridge. The absorption spectra of the complexes present a MLCT [Cu → π*(N(∧)N)] band in the λ 370-425 nm region. These new complexes exhibit red-orange MLCT-based emission in the solid-state with lifetimes in the microsecond range. In oxygen-free dichloromethane solution, the complex [Cu(2)(µ-dppm)(2)(µ-L(C))](2+) has a long lifetime of 22.8 µs. The long emission lifetimes are attributed to a rigid conformation that precludes the possible distortion of the copper in the excited state.

Photochemical [2 + 2] cycloaddition reactions of 6-alkenyl-3-phenylcyclohex-2-en-1-ones: using biradical conformation control to account for exceptions to the "rule of five".

A series of 6-alkenyl-3-phenylcyclohex-2-enones has been synthesised and the structures of the products obtained from them on irradiation have been determined. The 6-propenyl compounds afforded a tricyclic 'parallel' [2 + 2] cycloaddition product and a bicyclic enone resulting from hydrogen abstraction in the biradical intermediate. The 6-butenyl and 6-pentenyl analogues gave 'crossed' cycloaddition products only. Although the regiochemistry of these cycloaddition reactions cannot be explained in terms of the 'rule of five', it is compatible with the concept of 'biradical conformation control' which is based on a consideration of the energy and structure of the possible 1,4-biradical intermediates.

Thienyl directed polyaromatic C-C bond fusions: S-doped hexabenzocoronenes.

With a view to combining the desirable electronic and photochemical properties of hexabenzocoronene (HBC) and the C-C bond forming capabilities of thiophenes, 1-(3-thienyl)-2,3,4,5,6-penta(4-tert-butyl-phenyl)benzene (1) was oxidised using FeCl(3). The resulting products, superaromatic thiophene (2) and its 5,5'-dimer (3), are S-HBC systems and provide a new pair of spectral comparators.

Synthesis, characterisation and biological evaluation of N-(ferrocenyl)naphthoyl amino acid esters as anticancer agents.

A series of N-(ferrocenyl)naphthoyl amino acid esters 5-18 has been prepared by coupling ferrocenyl naphthoic acids 3-4 to alpha-amino acids and linear amino acids in the presence of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and 1-hydroxybenzotriazole (HOBt). The compounds were fully characterised by a range of NMR spectroscopic techniques, UV-Vis spectroscopy, mass spectrometry and cyclic voltammetry. X-ray crystallographic studies of the intermediate compounds 1-2 were also performed. Biological evaluation of the intermediates 1-2 and N-(ferrocenyl)naphthoyl amino acid esters 5-18 was performed in the H1299 non-small cell lung cancer (NSCLC) cell line and the Sk-Mel-28 metastatic melanoma cell line. The intermediates 1-2 failed to produce an effect in either cell line. Compounds 5-18 exhibited a strong anti-proliferative effect in the H1299 cell line, whilst the Sk-Mel-28 cells were slightly more resistant to these compounds. N-(6-ferrocenyl-2-naphthoyl)-gamma-aminobutyric acid ethyl ester 17 shows a particularly high activity in both the H1299 cell line (IC(50) = 0.62 +/- 0.07 microM) and the Sk-Mel-28 cell line (IC(50) = 1.41 +/- 0.04 microM).