Structural Determination of an Unusual CuI-Porphyrin-π-Bond in a Hetero-Pacman Cu-Zn-Complex

The synthesis and characterization of a hetero-dinuclear compound is presented, in which a copper(I) trishistidine type coordination unit is positioned directly above a zinc porphyrin unit. The close distance between the two coordination fragments is secured by a rigid xanthene backbone, and a unique (intramolecular) copper porphyrin-π-bond was determined for the first time in the molecular structure. This structural motif was further analyzed by temperature-dependent NMR studies: In solution at room temperature the coordinative bond fluctuates, while it can be frozen at low temperatures. Preliminary reactivity studies revealed a reduced reactivity of the copper(I) moiety towards dioxygen. The results adumbrate why nature is avoiding metal porphyrin-π-bonds by fixing reactive metal centers in a predetermined distance to each other within multimetallic enzymatic reaction centers.     

Substituents modification of meso-aryl BODIPYs for tuning photophysical properties

We successfully synthesized eight meso-aryl BODIPYs with 2,6-diethyl- or 1,2,6,7-tetraethyl substituents and characterized their photophysical properties. The steric hindrance resulting from the phenolic group in the meso-aryl moiety and the ethyl groups on the BODIPY core affected the synthesis of dipyrromethanes as an intermediate as well as the UV–Vis absorption and fluorescence emission of the BODIPYs due to the constrained rotation of the aryl ring. The potential use of the meso-hydroxyphenyl BODIPY as a pH sensor was also shown by the pH-dependent fluorescence emissions.     

A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-Pyridyl Zinc Porphyrins

Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct ¹H NMR spectrum in CDCl₃, which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the ¹H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin–ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.     

Influence of axial coordination on the photophysical property of excited state of zinc porphyrin

The phenomenon that metalloporphyrins are coordinated to axial ligands is very common especially in green-plant and photosynthetic bacteria, where such coordination impacts a signifi-cant effect on both the primary charge separation in the reaction center and energy transfer in an-tenna systems[1]. In addition, it plays a key role in photodynamic therapy and medicine synthesis in a sense that some metalloporphyrins have been assembled by coordination bonds to anti-cancer drugs, enhancing the se…     

Effects of coumarin substituents on the photophysical properties of newly synthesised phthalocyanine derivatives

In this study, synthesis of new ligands, 8-hydroxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin and 8-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin, and their phthalocyanines, 2,9,16,23-tetrakis[8-hexyloxy-3-(4-oxyphenyl)coumarin]-metal-free and metallophthalocyanines {M[Pc(OBzCou)₄] (M = 2H, Zn(II), Co(II); Bz: benzene; Cou: coumarin)} were synthesised. The novel chromogenic compounds were characterised by elemental analysis: ¹H NMR, ¹³C NMR, MALDI-TOF, IR and UV–vis spectral data. The effect of coumarin substituents on the photophysical properties of metal-free (H₂Pc) and zinc phthalocyanines (ZnPc) derivatives has been examined. Spectrophotometric measurements revealed that coumarin-substituted ZnPc derivatives were in the unaggregated form, whereas those of H₂Pc species were in aggregated form. It means that substitution of coumarin derivative prevents the cluster formation in the presence of zinc ion in the centre of Pc.     

Synthesis of novel rod-shaped and star-shaped fluorescent phosphane oxides--nonlinear optical properties and photophysical properties

The design of a new class of fluorophores is presented. Some push-pull chromophores (D-pi-A) containing polyphenylethynyl units and a phosphane oxide moiety were efficiently prepared from common intermediates. Straightforward syntheses gave novel one-armed, rod-shaped and three-armed, star-shaped fluorophores. The optical properties of the resulting star-shaped derivatives were evaluated, showed high fluorescence quantum yields, and their excitation induces very efficient charge redistribution. Moreover, thanks to their push-pull character, the molecules exhibited significant second-order NLO properties with good transparency, up to 67x10(-30) esu at 1907 nm, with an absorption lambdamax at 369 nm. The effect of the donor group and of the number of phenylethynyl arms have been studied in this work.     

Synthesis and photophysical properties of annulated dinuclear and trinuclear phthalocyanines

Metal-free mononuclear, dinuclear and trinuclear phthalocyanines were prepared by a mixed cyclotetramerisation of a 1,2,4,5-tetracyanobenzene derivative and 4,5-bis(2,6-dimethylphenoxy)phthalonitrile. For the first time, a pi-electron-conjugated trinuclear phthalocyanine was synthesised with phthalocyanine units connected by common annulated benzene rings. The Q band of the trinuclear compound in solution occurs at lambda = 944 nm whereas those of the dinuclear and mononuclear compounds are at lambda = 853/830 and 701/664 nm, respectively. Fluorescence quantum yields, fluorescence lifetimes and singlet-oxygen quantum yields of the compounds were determined.     

Design and photophysical properties of zinc(II) porphyrin-containing dendrons linked to a central artificial special pair

The click chemistry synthesis and photophysical properties, notably photo-induced energy and electron transfers between the central core and the peripheral chromophores of a series of artificial special pair-dendron systems (dendron = G1, G2, G3; Gx = zinc(II) tetra-meso-arylporphyrin-containing polyimides) built upon a central core of dimethylxanthenebis(metal(II) porphyrin) (metal = zinc, copper), are reported. The dendrons act as singlet and triplet energy acceptors or donors, depending on the dendrimeric systems. The presence of the paramagnetic d(9) copper(II) in the dendrimers promotes singlet-triplet energy transfer from the zinc(II) tetra-meso-arylporphyrin to the bis(copper(II) porphyrin) unit and slow triplet-triplet energy transfer from the central bis(copper(II) porphyrin) fragment to the peripheral zinc(II) tetra-meso-arylporphyrin. If bis(zinc(II) porphyrin) is the central core, evidence for chain folding is observed; this is unambiguously demonstrated by the presence of triplet-triplet energy transfer in the heterobimetallic systems, a process that can only occur at short distances.     

Hydrocarbon oxidation by beta-halogenated dioxoruthenium(VI) porphyrin complexes: effect of reduction potential (RuVI/V) and C-H bond-dissociation energy on rate constants

beta-Halogenated dioxoruthenium(VI) porphyrin complexes [Ru(VI)(F(28)-tpp)O(2)] [F(28)-tpp=2,3,7,8,12,13, 17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(VI)(beta-Br(8)-tmp)O(2)] [beta-Br(8)-tmp=2,3,7,8,12,13,17,18-octabromo-5,10,15,20- tetrakis(2,4,6-trimethylphenyl)porphyrinato(2-)] were prepared from reactions of [Ru(II)(por)(CO)] [por=porphyrinato(2-)] with m-chloroperoxybenzoic acid in CH(2)Cl(2). Reactions of [Ru(VI)(por)O(2)] with excess PPh(3) in CH(2)Cl(2) gave [Ru(II)(F(20)-tpp)(PPh(3))(2)] [F(20)-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato(2-)] and [Ru(II)(F(28)-tpp)(PPh(3))(2)]. The structures of [Ru(II)(por)(CO)(H(2)O)] and [Ru(II)(por)(PPh(3))(2)] (por=F(20)-tpp, F(28)-tpp) were determined by X-ray crystallography, revealing the effect of beta-fluorination of the porphyrin ligand on the coordination of axial ligands to ruthenium atom. The X-ray crystal structure of [Ru(VI)(F(20)-tpp)O(2)] shows a Ru=O bond length of 1.718(3) A. Electrochemical reduction of [Ru(VI)(por)O(2)] (Ru(VI) to Ru(V)) is irreversible or quasi-reversible, with the E(p,c)(Ru(VI/V)) spanning -0.31 to -1.15 V versus Cp(2)Fe(+/0). Kinetic studies were performed for the reactions of various [Ru(VI)(por)O(2)], including [Ru(VI)(F(28)-tpp)O(2)] and [Ru(VI)(beta-Br(8)-tmp)O(2)], with para-substituted styrenes p-X-C(6)H(4)CH=CH(2) (X=H, F, Cl, Me, MeO), cis- and trans-beta-methylstyrene, cyclohexene, norbornene, ethylbenzene, cumene, 9,10-dihydroanthracene, xanthene, and fluorene. The second-order rate constants (k(2)) obtained for the hydrocarbon oxidations by [Ru(VI)(F(28)-tpp)O(2)] are up to 28-fold larger than by [Ru(VI)(F(20)-tpp)O(2)]. Dual-parameter Hammett correlation implies that the styrene oxidation by [Ru(VI)(F(28)-tpp)O(2)] should involve rate-limiting generation of a benzylic radical intermediate, and the spin delocalization effect is more important than the polar effect. The k(2) values for the oxidation of styrene and ethylbenzene by [Ru(VI)(por)O(2)] increase with E(p,c)(Ru(VI/V)), and there is a linear correlation between log k(2) and E(p,c)(Ru(VI/V)). The small slope (approximately 2 V(-1)) of the log k(2) versus E(p,c)(Ru(VI/V)) plot suggests that the extent of charge transfer is small in the rate-determining step of the hydrocarbon oxidations. The rate constants correlate well with the C-H bond dissociation energies, in favor of a hydrogen-atom abstraction mechanism.     

Functional macromolecules from single-walled carbon nanotubes: synthesis and photophysical properties of short single-walled carbon nanotubes functionalised with 9,10-diphenylanthracene

9,10-Diphenylanthracene (DPA), a well-studied organic chromophore (Phi(fl) = 0.98) that exhibits electroluminescence, has been covalently bound through 2-(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single-walled carbon nanotubes (sSWNTs) of 1 microm average length, and the resulting DPA-functionalised sSWNT (DPA- sSWNT) macromolecular adducts (4.6 wt % DPA content) characterised by solution (1)H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of DPA fluorescence (steady-state and time-resolved) and of the transient optical spectra of sSWNTs and DPA-sSWNTs show that the covalent linkage boosts the interaction between the DPA and the sSWNT units. DPA-sSWNTs exhibit emission in the near-IR region from 1100-1400 nm with an enhanced quantum yield (Phi = 5.7x10(-3)) compared with sSWNTs (Phi = 3.9x10(-3)).     

Synthesis,Properties and Reactivity Studies of a Hetero-dicopper Complex Consisting of a Porphyrin and a Bispyridylamine Moiety Connected by a Xanthene Backbone

Synthesis, characterization and reactivity studies of a hetero-dicopper complex, particularly towards oxygen reduction are presented. A bischlorido copper(II) trishistidine-type coordination unit is positioned directly above a copper porphyrin unit. The close distance between the two coordination fragments is secured by a rigid xanthene backbone. Surprisingly, the dinuclear complex is not active towards oxygen reduction unlike the earlier published mononuclear analogues with a bispyridylamine copper center. However, the compound architecture of this multinuclear metal complex is interesting and can play an important role in the development of new catalysts for ORR.