Differently substituted phthalocyanines: Comparison of calculated energy levels, singlet oxygen quantum yields, photo-oxidative stabilities, photocatalytic and catalytic activities

Singlet oxygen generation for selective oxidation of emerging pollutants in a flow-by electrochemical system based on natural air diffusion cathode

The decay of free radicals involved in side reactions is one of the challenges faced by electrochemical degradation of organic pollutants. To this end, a non-radical oxidation system was constructed by a natural air diffusion cathode (ADC) and a Ti-based dimensional stable anode coated by RuO₂ (RuO₂-Ti anode) for cathodic hydrogen peroxide activation by anodic chlorine evolution. The ADC fabricated by the carbon black of BP2000 produced a stable concentration of hydrogen peroxide of 339.94 mg L^-1 (current efficiency of 73.4%) without aeration, which was superior to the cathode made by the XC72 carbon black. The flow-by ADC-RuO₂ system consisted of an ADC and a RuO₂-Ti anode showed high selectivity to aniline (AN) compared to benzoate (BA) in a NaCl electrolyte, whose degradation efficiencies were 97.72% and 1.3%, respectively. Rapid degradations of a mixture of emerging pollutants and AN were also observed in the ADC-RuO₂ system, with pseudo-first-order kinetic constants of 0.51, 1.29, 0.89, and 0.99 min^-1 for Bisphenol A (BPA), tetracycline (TC), sulfamethoxazole (SMX) and AN, respectively. Quenching experiments revealed the main reactive oxygen species for the pollutant degradation was singlet oxygen (¹O₂), which was also identified by the electron spin resonance (ESR) analysis. Finally, the steady-stable content of ¹O₂ was quantitatively determined to be 6.25 × 10^-11 M by the method of furfuryl alcohol (FFA) probe. Our findings provide a fast, low energy consumption and well controlled electrochemical oxidation method for selective degradation of organic pollutants. H₂O₂ generated on an air diffusion cathode by naturally diffused O₂, reacts with ClO^- produced from chloride oxidation on the RuO₂-Ti anode to form singlet oxygen (¹O₂). The electrochemical system shows an efficient oxidation to electron-rich emerging pollutants including bisphenol A, tetracycline, sulfamethoxazole and aniline, but a poor performance on the electron-deficient compounds (e.g., benzoate).

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation

In the present work, sixteen different zinc porphyrins (possessing different meso substituents) with and without a chiral guest were modelled using DFT and TD-DFT approaches in order to understand the influence of various controlling factors on electronic circular dichroism (ECD) spectra. Two major aspects are influenced by these factors: excitation energy of the electronic transitions and their intensity. In the case of excitation energy, the influence increases in the following order: orientation of the peripheral substituents Collapse

Key Words

• circular dichroism
• density functional calculations
• porphyrins
• supramolecular chemistry
• transition metals

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MESH Headings Collapse

Grants

• PUTJD749 Estonian Research Council
• PRG399 Estonian Research Council
• 828779 European Union's H2020-FETOPEN
• Estonian Research Council

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Affiliation(s)

Irina Osadchuk Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia ICGMUniv MontpellierCNRS, ENSCMMontpellierFrance
Riina Aav Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia
Victor Borovkov Department of Chemistry and BiotechnologySchool of ScienceTallinn University of Technology AddressAkadeemia tee 1512618TallinnEstonia
Eric Clot ICGMUniv MontpellierCNRS, ENSCMMontpellierFrance

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A versatile heterogeneous photocatalyst: nanoporous gold powder modified with a zinc(II) phthalocyanine derivative for singlet oxygen [4 + 2] cycloadditions

Nanoporous gold was functionalized with a photosensitizer, a zinc(II) phthalocyanine derivative. Such systems are active for the generation of reactive singlet oxygen which can be used for photocatalytic oxidation reactions. This study aims to demonstrate the versatility of such an approach, in terms of substrates and the employed solvent, only possible for a truly heterogeneous catalytic system. The activity of the hybrid system was studied for [4 + 2] cycloadditions of three different types of dienes and a total of eight substrates in two organic solvents and once in water. The highest activity was measured for 1,3-diphenylisobenzofuran, which is also highest in terms of sensitivity for the reaction with ¹O₂. Trends in conversion could be anticipated based on reported values for the rate constant for the reaction of ¹O₂. In almost all cases, an amplification of the conversion by immobilization of the sensitizer onto nanoporous gold was observed. The limiting case was ergosterol, which was the largest of all substrates with a van-der-Waals radius of about 2.1 nm. Additional factors such as the limited lifetime of ¹O₂ in different solvents as well as the hampered diffusion of the substrates were identified.

Comparison of the photocatalytic activity of novel hybrid photocatalysts based on phthalocyanines, subphthalocyanines and porphyrins immobilized onto nanoporous gold

A series of different singlet oxygen photosensitizers was immobilized onto nanoporous gold powder with a mean pore size of 40 nm via copper catalyzed azide-alkyne cycloaddition. The attachment of phthalocyanine and porphyrin derivatives was performed on the peripheral substituent of the macrocycle, whereas the subphthalocyanine derivatives were attached via the axial substituent with respect to the macrocyclic ring system. All obtained hybrid systems were studied in the photooxidation of 2,5-diphenylfuran as a chemical singlet oxygen quencher and showed increased photocatalytic activity compared to the same amount of the corresponding photosensitizer in solution due to photoinduced interactions of the plasmon resonance of the nanostructured gold support and the attached photosensitizer. The understanding of the different photophysical interactions depending on the coordination mode of the macrocycle as well as the position of the absorbance in the electromagnetic spectrum is an important point in the development towards highly active hybrid photocatalysts covering a broad absorption range within the spectrum of visible light.

Third-order nonlinear optical properties of axially modified indium phthalocyanines with alkyl chains

Novel axially substituted indium phthalocyanine with strong NLO properties: effects of the length of the alkyl chain.

A planar binuclear cobalt(ii) phthalocyanine as a highly efficient catalyst for the oxidation of a mercaptan

This paper reports on a binuclear Co(ii)Pc which exhibits a previously unknown extremely high catalytic activity for the oxidation of a thiol to the corresponding disulfide. The high activity is explained by an electronic contact between the two Co centres in the complex.

Conjugation of Phthalocyanine Photosensitizer with Poly(amidoamine) Dendrimer: Improved Solubility, Disaggregation and Photoactivity Against HepG2 Cells

OBJECTIVE

To improve solubility and to reduce aggregation, ZnPcC4 was conjugated to a third-generation poly-amidoamine dendrimer with amino end group (G3-PAMAM-NH2), which acts as a novel photodynamic therapy (PDT) drug carrier system.

METHODS

The phthalocyanines were synthesized by construction reaction. The nano drug was obtained from the conjugation of ZnPcC4 to G3-PAMAM-NH2, using EDC and NHS as coupling agents. The ZnPcC4@G3-PAMAM-NH2 conjugation was characterized by UV-Vis and MS. The 1O2 quantum yield of ZnPcC4@G3-PAMAM-NH2 in water was measured by the chemiluminescence method. The in vitro PDT responses of the studied photosensitizers were studied in hepatocellular carcinoma cell line HepG2 by MTT assay.

RESULTS

At ZnPcC4/G3-PAMAM-NH2 raw ratio of 100/1, the ZnPcC4 conjugate had improved solubility and reduced aggregation tendency in aqueous solution. At this optimum molar ratio, ZnPcC4- G3-PAMAM-NH2 inhibited HepG2 cells, with a half-maximal inhibitory concentration of 1.67 µg/mL upon infrared light exposure. The controls, including dark conditions, or media as well as G3-PAMAM-NH2 exposure, exhibited no inhibitory response.

CONCLUSION

The conjugation of phthalocyanine photosensitizer ZnPcC4 to poly-amidoamine dendrimer G3-PAMAM-NH2 improved the PDT outcomes, in which the optimized binding ratio of ZnPcC4 to G3-PAMAM-NH2 was 6:1.

Octa-substituted metallophthalocyanines bearing (2,3-dihydrobenzo-1,4-benzodioxin-2-yl)methoxy and chloro groups: Synthesis, characterization and photophysicochemical studies

In this study, the synthesis and characterization of novel 4-chloro-5-((2,3-dihydrobenzo-1,4-benzodioxin-2-yl)methoxy)phthalonitrile (1) and its peripherally octa-substituted Zn(II) (Pc-Zn), In(III) (PcInCI) and Mg(II) (Pc-Mg) phthalocyanine (Pc) derivatives are reported for the first time. FT-IR, elemental analysis, UV-vis, NMR and MS techniques were used for characterization studies of the compounds. Aggregation properties of the compounds were evaluated in DMF, DMSO and THF solvents in different concentrations, and the compounds did not tend to aggregate in these solvents. In addition, photophysicochemical properties such as fluorescence, photodegradation and singlet oxygen quantum yield of the compounds were examined in DMSO, DMF and THF solvents to show the potential use of these novel compounds as photosensitizers for photodynamic therapy (PDT). The effects of zinc, indium and magnesium metals, octa substitutions in peripheral positions and different types of solvents on photophysicochemical properties were investigated. The singlet oxygen quantum yield values of compounds ranged from 0.27 to 0.77 in different solvents. As a result of the photophysicochemical properties, these compounds can be considered as potential candidates for PDT, applications.

Improved targeting for photodynamic therapy via a biotin–phthalocyanine conjugate: synthesis, photophysical and photochemical measurements, and in vitro cytotoxicity assay

In this study, the peripherally biotin-substituted zinc(ii) phthalocyanine (Pc2) was synthesized as a photosensitizer for the treatment of cancer by photodynamic therapy.

Synergistic Effect in Zinc Phthalocyanine—Nanoporous Gold Hybrid Materials for Enhanced Photocatalytic Oxidations

Nanoporous gold (npAu) supports were prepared as disks and powders by corrosion of Au-Ag alloys. The npAu materials have pore sizes in the range of 40 nm as shown by scanning electron microscopy (SEM). The surface was modified by a self-assembled monolayer (SAM) with an azidohexylthioate and then functionalized by a zinc (II) phthalocyanine (ZnPc) derivative using “click chemistry”. By atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) the content of zinc was determined and the amount of immobilized ZnPc on npAu was calculated. Energy-dispersive X-ray (EDX) spectroscopy gave information about the spatial distribution of the ZnPc throughout the whole porous structure. NpAu and ZnPc are both absorbing light in the visible region, therefore, the heterogeneous hybrid systems were studied as photocatalysts for photooxidations using molecular oxygen. By irradiation of the hybrid system, singlet oxygen is formed, which was quantified using the photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a selective singlet oxygen quencher. The illuminated surface area of the npAu-ZnPc hybrid system and the coverage of the ZnPc were optimized. The synergistic effect between the plasmon resonance of npAu and the photosensitizer ZnPc was shown by selective irradiation and excitation of only the phthalocyanine, the plasmon resonance of the npAu support and both absorption bands simultaneously, resulting in an enhanced photooxidation activity by nearly an order of magnitude.

Synthesis, characterization, photophysicochemical properties and theoretical study of novel zinc phthalocyanine containing four tetrathia macrocycles

In this work, Zn(II) phthalocyanine derivative (TTU-Pc) bearing 13-membered tetrathia macrocycles was synthesized, and the novel Zn(II) phthalocyanine derivative was fully characterized by elemental analysis and general spectroscopic methods such as MALDI-TOF mass, FT-IR, UV-vis and [Formula: see text]H-NMR. The synthesized phthalocyanine derivative has quite limited solubility in most of the common organic solvents. Fluorescence measurement was conducted for this Zn(II)phthalocyanine to estimate its fluorescence quantum yields. The singlet oxygen generation ability was also examined to investigate its photosensitizer properties. General trends were described for quantum yields of fluorescence, photodegradation and singlet oxygen quantum yields of this compound. The electrochemical properties of the molecule were investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). In addition, the lowest energy structure, the electronic structure and frontier molecular orbitals were calculated in DFT and the excitation spectrum was obtained by TDDFT calculations. We found that our computational and experimental results were in agreement.

Singlet oxygen quantum yields and photostability of planar binuclear phthalocyanines

The singlet oxygen ([Formula: see text]O[Formula: see text] quantum yield of the near-infrared absorbing ([Formula: see text] [Formula: see text] 839 nm) planar [Formula: see text]-conjugated binuclear zinc phthalocyanine (ZnPc) was measured and compared to the [Formula: see text]O[Formula: see text] quantum yields of the mononuclear and the planar binuclear phthalocyanine without [Formula: see text]-conjugation between Pc rings. In addition, the photooxidative stability of the [Formula: see text]-conjugated binuclear Pc was determined and compared to the stabilities of the mononuclear ZnPc and the known near-infrared photosensitizer, zinc tetra-tert-butylnaphthalocyanine ([Formula: see text] 761 nm). The results are explained by DFT calculations and cyclic voltammetry.

A single-light triggered and dual-imaging guided multifunctional platform for combined photothermal and photodynamic therapy based on TD-controlled and ICG-loaded CuS@mSiO2

Near-infrared (NIR)-responsive drug delivery systems have received enormous attention because of their good biocompatibility and high biological penetration. In this work, we report a novel 1-tetradecanol (TD)-controlled and indocyanine green (ICG)-loaded CuS@mSiO₂ phototherapy nanoplatform (CuS@mSiO₂-TD/ICG). The CuS@mSiO₂ nanoparticles prepared by a facile one-pot approach can serve as drug-delivery vehicles to transport the NIR absorbing phototherapeutic agent (ICG) within the mesoporous cavities. Meanwhile a phase-change molecule (PCM), TD, is introduced as a thermosensitive gatekeeper to avoid the premature release of loaded ICG. Noticeably, the combined therapy is irradiated at an 808 nm single-light wavelength, thus performing the photothermal therapy (PTT) based on CuS@mSiO₂ as well as simultaneously triggering the photodynamic (PDT)/PTT effect based on ICG. Furthermore, ICG also has the function of dual in vivo fluorescence imaging and photoacoustic (PA) imaging. This dual imaging-guided and gatekeeper-controlled nanoplatform for the single-light triggered PTT/PDT treatment holds significant promise for future cancer therapy due to their markedly improved therapeutic efficacy and decreased systemic toxicity.

Tuning the Structure and Photophysics of a Fluorous Phthalocyanine Platform

Phthalocyanines are an important class of industrial dyes with potential commercial applications ranging from photovoltaics to biomedical imaging and therapeutics. We previously demonstrated the versatility of the commercially available zinc(II) hexadecafluorophthalocyanine (ZnF16Pc) as a platform for rapidly developing functional materials for these applications and more. Because this core-platform approach to dye development is increasingly common, it is important to understand the photophysical and structural consequences of the substitution chemistry involved. We present a fundamental study of a series of ZnF16Pc derivatives in which the aromatic fluorine atoms are progressively substituted with thioalkanes. Clear spectroscopic trends are observed as the substituents change from electron-withdrawing to electron-releasing groups. Additionally, there is evidence for significant structural distortion of the normally planar heterocycle, with important ramifications for the photophysics. These results are also correlated to DFT calculations, which show that the orbital energies and symmetries are both important factors for explaining the excited-state dynamics.

The effects of central metals on the photophysical and nonlinear optical properties of reduced graphene oxide-metal(II) phthalocyanine hybrids

Reduced graphene oxide-metal(II) phthalocyanine (RGO-MPc, M = Cu, Zn and Pb) hybrid materials have been prepared by the covalent functionalization method. The resultant RGO-MPc hybrids are characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, ultraviolet-visible absorption and fluorescence spectroscopy. The RGO-MPc hybrids exhibit strong fluorescence quenching by means of the photo-induced electron transfer or the energy transfer (PET/ET) process between the RGO and MPc moieties. The PET/ET process particularly depends on the fluorescence quantum yield of MPc molecules with different central metals. The nonlinear optical (NLO) properties of the RGO-MPc hybrids are investigated by using the Z-scan technique at 532 nm with 4 ns laser pulses. The results show that the NLO properties of MPc molecules increase in the order of Zn < Pb < Cu, but the RGO-MPc hybrids exhibit NLO performance in the inverse sequence of Zn > Pb > Cu, implying that the NLO response arising from the efficient PET/ET process between RGO and MPc may play a more important role in the NLO properties of RGO-MPc hybrids than that originating from the MPc moiety.

Modulation of the electronic and spectroscopic properties of Zn(II) phthalocyanines by their substitution pattern

Four isomerically pure octasubstituted zinc phthalocyanines with variations in the attachment atom and positions of the substituents were selected for a systematic investigation of the effect of the substitution pattern on their electronic and spectroscopic properties. Effects which were investigated are the position, the electron donating and withdrawing properties, and the donating force of the substituent. The results are discussed and interpreted based on theoretical and experimental determination of the orbital levels. This work allows us to highlight which substitution patterns are the most suitable considering different common applications of phthalocyanines.

Production of reactive oxygen and nitrogen species by light irradiation of a nitrosyl phthalocyanine ruthenium complex as a strategy for cancer treatment

Production of reactive oxygen species has been used in clinical therapy for cancer treatment in a technique known as Photodynamic Therapy (PDT). The success of this therapy depends on oxygen concentration since hypoxia limits the formation of reactive oxygen species with consequent clinical failure of PDT. Herein, a possible synergistic effect between singlet oxygen and nitric oxide (NO) is examined since this scenario may display increased tumoricidal activity. To this end, the trinuclear species [Ru(pc)(pz)2{Ru(bpy)2(NO)}2](PF6)6 (pc = phthalocyanine; pz = pyrazine; bpy = bipyridine) was synthesized to be a combined NO and singlet oxygen photogenerator. Photobiological assays using at 4 × 10(-6) M in the B16F10 cell line result in the decrease of cell viability to 21.78 ± 0.29% of normal under light irradiation at 660 nm. However, in the dark and at the same concentration of compound , viability was 91.82 ± 0.37% of normal. The potential application of a system like in clinical therapy against cancer may be as an upgrade to normal photodynamic therapy.

Effects of position (α or β) and linker heteroatom (O or S) of substituent on the photophysicochemical behavior of poly(oxyethylene) substituted ZnPcs and assessment of J-aggregation or protonation using TD-DFT computations

A series of zinc phthalocyanines (ZnPcs) tetra-substituted with 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanol () or 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanethiol () at peripheral (β) () and non-peripheral (α) () positions have been synthesized and characterized. The spectroscopic, photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation) properties of these newly synthesized phthalocyanines have been investigated in DMSO. The effects of the position of the substituents on the phthalocyanine skeleton and the nature of the linker heteroatom on their spectroscopic, photophysical and photochemical properties have been determined. The quenching behavior of the zinc phthalocyanines by 1,4-benzoquinone has been studied in DMSO. All of the zinc(ii) Pc complexes ( and ) showed similar electronic absorption spectra in various solvents (chloroform, dichloromethane, DMF, DMSO, THF and toluene). However, complex gave an extra red-shifted band at 742 nm in chloroform and dichloromethane. DFT and TD-DFT computations were performed on the model structures (, and ) to find out the cause of the extra red-shifted Q band (J-type aggregation or protonation of the Pc ring). The computational results showed that monoprotonation of a meso nitrogen atom leads to the formation of this extra band. Photophysical and photochemical measurements indicated that these newly synthesized ZnPc derivatives are promising candidates for use as photosensitizers in the application of PDT.

An aptamer-based biosensor for sensitive thrombin detection with phthalocyanine@SiO2 mesoporous nanoparticles

Silica nanoparticles, with entrapped hydrophobic photosensitizer tetra-α-(2, 4-di-tert-butylphenoxy)-phthalocyaninato zinc (ZnPc(OAr)4), were synthesized by hydrolyzing triethoxyvinylsilane (TEVS) and 3-amino propyl triethoxysilane (APTES). The as-prepared nanoparticles, which were highly monodispersed spheres (about 100 nm), exhibited strong Q-band absorption of ZnPc(OAr)4 centered at 701 nm. The aqueous solubility of ZnPc(OAr)4 encapsulated in silica nanoparticles was obviously improved. The nanoparticles efficiently generated singlet oxygen ((1)O2) both in organic and aqueous solutions after being irradiated at suitable wavelength. The resulting (1)O2 then initiated chemiluminescence (CL) by reacting with a methyl cypridina luciferin analog (MCLA). Based on the photoinduced CL, a sensitive aptamer-based sandwich-type sensor was presented to detect human thrombin. Thrombin was first attached to Pc@SiO2 via secondary aptamer, and then they were collected, for CL determination, by beads with primary aptamer. The proposed approach, which was highly selective with a low detection limit of 80 pmol/L, minimized the nonspecific adsorption. Such an aptamer-based biosensor is feasible in screening biomarkers in complex matrices at ultratrace levels.

Selective photodynamic therapy induced by preirradiation of galactopyranosyl Zn(II) phthalocyanines with UV and red lights

The challenging task in the photodynamic therapy is the optimization of the procedure in a way to reach maximal selectivity of the phototoxic effect to tumor vs. non-neoplastic cells. The present study explores the impact of the light exposure with harmless UV 365 nm and low intensity visible red 637 nm light during incubation period on the uptake, primary localization, re-localization and photocytotoxic effect of tetra-galactopyranosyl substituted Zn ( II ) phthalocyanines. The studies were carried out on cancer cells (MDA-MB-231) and on non-tumorigenic cells (Balb/c 3T3, clone 31). The experimentals suggested that in addition to the favorable chemical structure of the applied amphiphilic protected galactose Zn ( II ) phthalocyanines, the pretreatment with UV 365 nm and visible red 637 nm light applied prior therapeutic light, lead to selective phototoxic effects on tumor cells.

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 12. New heteropentanuclear complexes carrying four exocyclic cis-platin-like functionalities as potential bimodal (PDT/cis-platin) anticancer agents

Heteropentanuclear porphyrazines having the formula [(PtCl2)4LM] where L = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato dianion and M = Zn(II), Mg(II)(H2O), Pd(II), Cu(II) or Co(II) were characterized by elemental analyses, IR-UV-visible spectroscopy and electrochemistry and the data compared to new and previously published results for the corresponding homopentanuclear compound [(PtCl2)4LPt]. This latter species has four external N2(py)PtCl2 coordination sites which closely resemble cis-platin, (NH3)2PtCl2, the potent chemotherapeutic anticancer drug, and is able to act as a photosensitizer for the generation of (1)O2, the cytotoxic agent in photodynamic therapy (PDT). UV-visible spectra and half wave potentials for reduction of [(PtCl2)4LM], [(PtCl2)4LPt], the parallel series of mononuclear [LM] compounds and the pentanuclear [(PdCl2)4LM] compounds were examined in the nonaqueous solvents dimethyl sulfoxide, pyridine, and dimethylformamide. The complete set of available data indicate that external coordination of the PtCl2 and PdCl2 units significantly increases the level of the electron-deficiency of the entire molecular framework despite the fact that these groups are far away from the central porphyrazine π-ring system and have coordination sites nearly orthogonal to the plane of the macrocycle. The pentanuclear species [(M'Cl2)4LM] (M' = Pt(II), Pd(II)) undergo multiple one-electron transfers and exhibit an easier reducibility as compared to related electrode reactions of the parent compounds [LM] having the same central metal. Aggregation phenomena and reducibility of the porphyrazines to their monoanionic form (prevalently in DMF) are observed for some of the examined compounds and were analyzed and accurately taken into account. Quantum yields of (1)O2 (ΦΔ), of interest in PDT, were measured for [(PtCl2)4LM] with M = Zn(II), Mg(II)(H2O), or Pd(II) and the related macrocycles [(PdCl2)4LM] and [LM] in dimethylformamide (DMF) and/or DMF preacidified with HCl (DMF/HCl, [HCl]: 1-2 × 10(-4) M). Excellent ΦΔ values (0.5-0.6) which qualify the compounds as potent photosensitizers in PDT were obtained for the pentanuclear species having Zn(II) or Pd(II) as central metal ions. The [(PtCl2)4LZn] and [(PtCl2)4LPd] complexes are of special interest as potential bimodal anticancer agents because of the incorporated four cis-platin-like functionalities.

Controlled chain polymerisation and chemical soldering for single-molecule electronics

Single functional molecules offer great potential for the development of novel nanoelectronic devices with capabilities beyond today's silicon-based devices. To realise single-molecule electronics, the development of a viable method for connecting functional molecules to each other using single conductive polymer chains is required. The method of initiating chain polymerisation using the tip of a scanning tunnelling microscope (STM) is very useful for fabricating single conductive polymer chains at designated positions and thereby wiring single molecules. In this feature article, developments in the controlled chain polymerisation of diacetylene compounds and the properties of polydiacetylene chains are summarised. Recent studies of "chemical soldering", a technique enabling the covalent connection of single polydiacetylene chains to single functional molecules, are also introduced. This represents a key step in advancing the development of single-molecule electronics.