Porphyrin-polymer nanocompartments: singlet oxygen generation and antimicrobial activity

A new water-soluble photocatalyst for singlet oxygen generation is presented. Its absorption extends to the red part of the spectrum, showing activity up to irradiation at 660 nm. Its efficiency has been compared to that of a commercial analogue (Rose Bengal) for the oxidation of L-methionine. The quantitative and selective oxidation was promising enough to encapsulate the photocatalyst in polymersomes. The singlet oxygen generated in this way can diffuse and remain active for the oxidation of L-methionine outside the polymeric compartment. These results made us consider the use of these polymersomes for antimicrobial applications. E. coli colonies were subjected to oxidative stress using the photocatalyst-polymersome conjugates and nearly all the colonies were damaged upon extensive irradiation while under the same red LED light irradiation, liquid cultures in the absence of porphyrin or porphyrin-loaded polymersomes were unharmed.

Luminescent copper(i) complexes with bisphosphane and halogen-substituted 2,2′-bipyridine ligands

Light-emitting electrochemical cells with Cu(i) emitters with halo-substituted 2,2′-bipyridine ligands display orange electroluminescence and short turn-on times.

Copper(i) and silver(i) complexes of 9,9-dimethyl-4,5-bis(di-tert-butylphosphino)xanthene: photophysical properties and structural rigidity under pressure

Structural, photophysical and electrochemical properties of heteroleptic copper(i) and silver(i) complexes [M(tBu-xantphos)(bpy)][PF₆] are described where tBu-xantphos is 4,5-bis(di-tert-butylphosphino)-9,9-dimethylxanthene.

Design and Characterization of an Electrically Powered Single Molecule on Gold

The surface diffusion of individual molecules is of paramount importance in self-assembly processes and catalytic processes. However, the fundamental understanding of molecule diffusion peculiarities considering conformations and adsorption sites remain poorly known at the atomic scale. Here, we probe the 4'-(4-tolyl)-2,2':6',2″-terpyridine adsorbed on the Au(111) herringbone structure combining scanning tunneling microscopy and atomic force microscopy. Molecules are controllably translated by electrons excitations over the reconstruction, except at elbows acting as pinning centers. Experimental data supported by theoretical calculations show the formation of coordination bonds between the molecule and Au atoms of the surface. Using force spectroscopy, we quantify local variation of the surface potential and the lateral force required to move the molecule. We found an elevation of the diffusion barrier at elbows of the reconstruction of ∼100 meV compared to the rest of the surface.

4,2':6',4"- and 3,2':6',3"-Terpyridines: The Conflict between Well-Defined Vectorial Properties and Serendipity in the Assembly of 1D-, 2D- and 3D-Architectures

A comparative investigation of the coordination assemblies formed between Co(NCS)₂ and two monotopic 4,2':6',4''-terpyridine (4,2':6',4"-tpy) ligands or two related ditopic ligands is reported. Crystals were grown by layering MeOH solutions of Co(NCS)₂ over a CHCl₃ or 1,2-C₆H₄Cl₂ solution of the respective ligand at room temperature. With 4'-(2-methylpyrimidin-5-yl)-4,2':6',4"-terpyridine (6), the 1D-coordination polymer {[Co₂(NCS)₄(MeOH)₄(6)₂]∙2MeOH∙8H₂O}n assembles with 6 coordinating only through the outer N-donors of the 4,2':6',4"-tpy unit; coordination by the MeOH solvent blocks two cobalt coordination sites preventing propagation in a higher-dimensional network. A combination of Co(NCS)₂ and 1-(4,2':6',4"-terpyridin-4'-yl)ferrocene (7) leads to {[Co(NCS)₂(7)₂]∙4CHCl₃}n which contains a (4,4) net; the 2D-sheets associate through π-stacking interactions between ferrocenyl and pyridyl units. A 3D-framework is achieved through use of the ditopic ligand 1,4-bis(npropoxy)-2,5-bis(4,2':6',4"-terpyridin-4'-yl)benzene (8) which acts as a 4-connecting node in {[Co(NCS)₂(8)₂].2C₆H₄Cl₂}n; the combination of metal and ligand planar 4-connecting nodes results in a {6⁵.8} cds net. For a comparison with the coordinating abilities of the previously reported 1,4-bis(noctoxy)-2,5-bis(4,2':6',4"-terpyridin-4'-yl)benzene (3), a more flexible analogue 9 was prepared. {[Co(NCS)₂(9)]∙2CHCl₃}n contains a (4,4) net defined by both metal and ligand planar 4-connecting nodes. The noctoxy tails of 9 protrude from each side of the (4,4) net and thread through adjacent sheets; the arene-attached noctoxy chains associate through a combination of van der Waals and C-H...π interactions.

Coordination Behaviour of 1-(4,2′:6′,4′′-terpyridin-4′-yl)ferrocene and 1-(3,2′:6′,3′′-terpyridin-4′-yl)ferrocene: Predictable and Unpredictable Assembly Algorithms

The reaction of 1-(4,2′:6′,4″-terpyridin-4′-yl)ferrocene (2) with ZnI2 leads to [{ZnI2(2)}4·1.4MeOH·0.8H2O] which contains a discrete [4+4] metallocycle. Crystal growth experiments demonstrate that reactions of 2 with Zn(OAc)2 or CuCl2 result in the formation of single- or double-stranded 1D polymer chains, respectively, the latter facilitated by the formation of {Cu2Cl4} dinuclear nodes. While both 2 and its isomer 1-(3,2′:6′,3″-terpyridin-4′-yl)ferrocene (3) present V-shaped donor sets, rotation about interannular bonds in 3 generates flexible vectorial properties associated with limiting convergent and divergent orientations of the nitrogen donors. The synthesis and characterisation of 3 are described as are reactions of 3 with ZnCl2 or ZnBr2 which lead, respectively, to a metallosquare in [{ZnCl2(3)}4·3CHCl3·3MeOH] or a helical polymer in [{ZnBr2(3)}·MeOH]n. The tight pitch of the helix in the latter (8.7879(9) Å) is controlled by a combination of the orientations of the N,N″-donor sets in 3, and intra-chain π-stacking interactions involving ferrocenyl and pyridine units.

Absolute ion hydration enthalpies and the role of volume within hydration thermodynamics

This paper reports that various thermodynamic properties in aqueous media for certain individual ions and for compounds are linear functions of the inverse cube root of the solid respective ionic and compound solid state volumes, V_m^−1/3.

Homoleptic complexes of a porphyrinatozinc(ii)-2,2′:6′,2′′-terpyridine ligand

The syntheses and electrochemical and photophysical properties of the homoleptic complexes [Zn(1)₂][PF₆], [Fe(1)₂][PF₆] and [Ru(1)₂][PF₆] where 1 is the metalloligand 7-(4-([2,2′:6′,2′′-terpyridin]-4′-yl)phenyl)-5,10,15,20-tetraphenylporphyrinatozinc(ii) are reported.

The effects of introducing sterically demanding aryl substituents in [Cu(N^N)(P^P)]+ complexes

[Cu(6-Arbpy)(POP)][PF₆] and [Cu(6-Arbpy)(xantphos)][PF₆] compounds in which Ar is a sterically hindered aryl substituent are described; structural and solution dynamical consequences of the bulky groups are investigated.

Probing the mystery of Liesegang band formation: revealing the origin of self-organized dual-frequency micro and nanoparticle arrays

Periodic precipitation processes in gels can result in impressive micro- and nanostructured patterns known as periodic precipitation (or Liesegang bands). Under certain conditions, the silver nitrate-chromium(vi) system exhibits the coexistence of two kinds of Liesegang bands with different frequencies. We now present that the two kinds of bands form independently on different time scales and the pH-dependent chromate(vi)-dichromate(vi) equilibrium controls the formation of the precipitates. We determined the spatial distribution and constitution of the particles in the bands using focused ion beam-scanning electron microscopy (FIB-SEM) and scanning transmission X-ray spectromicroscopy (STXM) measurements. This provided the necessary empirical input data to formulate a model for the pattern formation; a model that quantitatively reproduces the experimental observations. Understanding the pattern-forming process at the molecular level enables us to tailor the size and the shape of the bands, which, in turn, can lead to new functional architectures for a range of applications.

'Active Surfaces' as Possible Functional Systems in Detection and Chemical (Bio) Reactivity

This article presents design strategies to demonstrate approaches to generate functionalized surfaces which have the potential for application in molecular systems; sensing and chemical reactivity applications are exemplified. Some applications are proven, while others are still under active investigation. Adaptation and extension of our strategies will lead to interfacing of different type of surfaces, specific interactions at a molecular level, and possible exchange of signals/cargoes between them. Optimization of the present approaches from each of five research groups within the NCCR will be directed towards expanding the types of functional surfaces and the properties that they exhibit.

The emergence of copper(I)-based dye sensitized solar cells

Since the discovery of Grätzel-type dye sensitized solar cells (DSCs) in the early 1990s, there has been an exponential growth in the number of publications dealing with their optimization and new design concepts. Conventional Grätzel DSCs use ruthenium(II) complexes as sensitizers, and the highest photon-to-electrical current conversion efficiency for a ruthenium dye is ≈12%. However, ruthenium is both rare and expensive, and replacement by cheaper and more sustainable metals is desirable. In this Tutorial Review, we describe strategies for assembling copper(I) complexes for use as dyes in DSCs, a research area that has been active since ≈2008. We demonstrate design principles for (I) ligands to anchor the complex to a semiconductor surface and promote electron transfer from dye to semiconductor, and (II) ancillary ligands to tune the light absorption properties of the dye and facilitate electron transfer from electrolyte to dye in the DSC. We assess the progress made in terms of light-harvesting and overall photoconversion efficiencies of copper(I)-containing DSCs and highlight areas that remain ripe for development and improvement.

A self-assembled, multicomponent water oxidation device

Langmuir-Blodgett (LB) and drop-cast (DC) films prepared from [Ru(1)3][PF6]2 and Co4POM (1= 4,4'-bis((n)nonyl)-2,2'-bipyridine, Co4POM = K10[Co4(H2O)2(α-PW9O34)2]) have been evaluated as water oxidation catalysts and their electrocatalytic performances are reported; DC films evolve more O2 per unit area than LB films and the catalyst is stable on an FTO surface for ≈500-600 minutes.

Positional isomerism makes a difference: phosphonic acid anchoring ligands with thienyl spacers in copper(i)-based dye-sensitized solar cells

With the aim of improving the photoconversion efficiencies of heteroleptic [Cu(Lanchor)(Lancillary)](+) dyes in n-type dye-sensitized solar cells (DSCs), the previously favoured anchor ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid) (1) has been replaced by analogues 2 and 3 containing 2-thienyl spacers between the 2,2'-bipyridine metal-binding domain and the phosphonic acid anchoring groups. The synthesis and characterization of 2 and 3 (2-thienyl spacer with phosphonic acid in the 5- and 4-positions, respectively) are reported. A stepwise, on-surface method was used to assemble [Cu(Lanchor)(Lancillary)](+) dyes onto FTO/TiO2 electrodes with Lanchor = 1, 2 or 3, and Lancillary = 6,6'-bis(trifluoromethyl)-2,2'-bipyridine (4), 6-trifluoromethyl-2,2'-bipyridine (5), 6,6'-dimethyl-2,2'-bipyridine (6), and 6-methyl-2,2'-bipyridine (7). Changing the solvent in the dye-bath from CH2Cl2 to acetone had only a small effect on the photoconversion efficiencies of [Cu(1)(4)](+), [Cu(1)(5)](+) and [Cu(1)(6)](+); the optimal dye in this series was [Cu(1)(5)](+). Comparable DSC performances were achieved by using either anchor 1 or 2, but there is improved electron injection if the phosphonic acid group is in the 4- rather than 5-position of the thienyl ring (i.e. anchor 3 is superior to 2). Similar open-circuit voltages (VOC) are achieved on going from 1 to 3 with a given Lancillary; although there is typically a gain in short-circuit current denisty (JSC) on going from 1 or 3 to 2, there is an ≈50-60 mV drop in VOC on introducing 2 as the anchor. The best photoconversion efficiencies are obtained for the dye [Cu(3)(5)](+) (η = 2.40% relative to an N719 reference of 5.76%). The conclusions reached from plots of current-density (J) against potential (V), and external quantum efficiency spectra are supported by electrochemical impedance spectroscopic measurements.

Constructing chiral MOFs by functionalizing 4,2′:6′,4′′-terpyridine with long-chain alkoxy domains: rare examples of neb nets

Three chiral 3D MOFs with uncommon neb topologies assemble from Co(NCS)₂ and 4′-(4-ⁿalkyloxyphenyl)-4,2′:6′,4′′-terpyridines (alkyl = hexyl or nonyl).