Charge-transfer photochemistry of bis(diethyl-diselenocarbamato)copper(II)

The photochemical reactions of bis(diethyl-diselenocarbamato)copper(II), Cu(Et2dsc)2, complex have been studied in toluene, CH2Cl2, CHCl3 and chloroalkane/EtOH mixed solvents. Charge-transfer irradiation induces intramolecular oxidation of the ligand and reduction of copper(II) to copper(I) as evidenced by EPR and UV-Vis spectra of the complex as well as quantum yield results. When photolysis is carried out in CHCl3 or CH2Cl2 or in the solvent mixture CHCl3/EtOH resp. CH2Cl2/EtOH of lower than 1:1 EtOH content, the primary photoproduct CuI(Et2dsc) is further oxidised in a dark reaction with the chloroalkane producing the corresponding paramagnetic mixed-ligand CuII(Et2dsc)Cl complex in equilibrium with its chloride-bridged and EPR silent, dimeric form Cu2(Et2dsc)2Cl2. At low concentration of EtOH the equilibrium is shifted to the dimeric form whereas at higher than 1:1 EtOH content in the mixed solvent CHCl3/EtOH it is shifted to CuII(Et2dsc)Cl. A reaction mechanism is proposed and the role of ethanol is discussed.     

Liquid-crystalline bisadducts of [60]fullerene

A second-generation cyanobiphenyl-based dendrimer was used as a liquid-crystalline promoter to synthesize mesomorphic bisadducts of [60]fullerene. Liquid-crystalline trans-2, trans-3, and equatorial bisadducts were obtained by condensation of the liquid-crystalline promoter, which carries a carboxylic acid function, with the corresponding bisaminofullerene derivatives. A monoadduct of fullerene was also prepared for comparative purposes. All the compounds gave rise to smectic A phases. An additional mesophase, which could not be identified, was observed for the trans-2 derivative. The supramolecular organization of the monoadduct derivative is governed by steric constraints. Indeed, for efficient space filling, adequacy between the cross-sectional areas of fullerene (approximately 100 A(2)) and of the mesogenic groups (approximately 22-25 A(2) per mesogenic group) is required. As a consequence, the monoadduct forms a bilayered smectic A phase. The supramolecular organization of the bisadducts is essentially governed by the nature and structure of the mesogenic groups and dendritic core. Therefore, the bisadducts form monolayered smectic A phases. The title compounds are promising supramolecular materials as they combine the self-organizing behavior of liquid crystals with the properties of fullerene.     

Effect of solvent and remote ligand substituents on the photochemical behaviour of copper(II) dithiocarbamates and dithiophosphates

The photochemical properties of bis(dithiocarbamato)Cu^II, Cu(R¹dtc)₂, and bis(dithiophosphato)Cu^II, Cu(R₂ ²dtp)₂, complexes with different remote ligand substituents (R¹ = piperidine, morpholine, pyrrolidine and 4-phenylpiperazine; R² = Me, Et and i-Pr) have been studied in chloromethanes (CCl₄, CHCl₃, CH₂Cl₂), chloromethanes/EtOH and PhMe. The monomeric species Cu^II(R¹dtc)Cl and its chloride-bridged dimeric form Cu₂(R¹dtc)₂Cl₂ were subsequently obtained during Cu(R¹dtc)₂ photolysis in chloromethane/EtOH mixtures and the steady-state concentration of Cu₂(R¹dtc)₂Cl₂ was found to depend on the EtOH content in the mixed solvents as well as on the nature of R¹ and the oxidising ability of the chloromethane. The appearance of the mixed-ligand complex Cu^II(R₂ ²dtp)Cl has been observed as an intermediate photoproduct after longer u.v.-irradiation of Cu(R₂ ²dtp)₂ in chloromethanes/EtOH.     

Diffraction under total internal reflection for micro-fluidic analysis

This work presents the principles of a novel micro-optical system for micro- and nano-fluidic analysis. It is based on diffraction, occurring in total internal reflection conditions. The developed detector is integrated in an autonomous micro-fluidic device, produced by a unique combination of different techniques for micro- and nano-structuring and micro-machining. The micro-fluidic sensor is examined both experimentally and theoretically with respect to the parameters of the light and the diffraction grating. The most beneficial configurations with respect to maximum sensitivity towards the fluidic optical constants are discussed. Optical experiments show sensitivity of 5×10^-4 to the fluidic refractive index and of 3.5×10⁶ m^-1 to the absorption coefficient. Envisioned applications of the integrated micro-sensor are concentration and composition analysis, environmental protection control, medical, biological and chemical diagnostics, and so on. PACS 07.07.Df; 81.16.-c; 78.20.Ci; 81.70.Jb     

Clay-fulleropyrrolidine nanocomposites

In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.     

Testing electron transfer within molecular associates built around anionic C60 and C70 dendrofullerenes and a cationic zinc porphyrin

Mono- and bis-functionalized C(60) and C(70) fullerene derivatives (DF, 1-10) that carry one or two oligoanionic dendritic termini in their malonate addends and an oligocationic octapyridinium zinc porphyrin salt (ZnP) were found to self-assemble in buffered aqueous solution to yield a novel series of 1:1 and/or 1:2 electron transfer hybrid associates. Remarkably high association constants-typically on the order of 10(8) M(-1)-were derived that corroborate stable complex formations. A combination of electrostatic and charge-transfer interactions that are operative between the electron-accepting DF and the electron-donating ZnP is considered to contribute to the uniquely high complex stability. First insight into intracomplex excited state interactions came from steady-state and time-resolved fluorescence quenching experiments that were performed with the molecular ZnP/DF hybrid associates. Excited state quenching processes are, for example, evident in form of a bi-exponential fluorescence decay of ZnP-corresponding to a distribution of associated and non-associated ZnP. Unambiguous evidence for an intracomplex electron transfer quenching, namely, formation of ZnP(.+)/C(60) (.-) and ZnP(.+)/C(70) (.-) radical ion pairs, was gathered in time-resolved transient absorption measurements. Lifetimes of these radical ion-pairs range from nanoseconds to a few microseconds.     

EPR study on the photoinduced electron transfer in the ternary complex (dithiocarbamato,dithiophosphato)copper(II)

The EPR study on equimolar solutions of Cu(dtc)₂ and Cu(dtp)₂ in aerated acetone, toluene and chloroalkane (CHCl₃ and CCl₄) solutions indicates that Cu(dtc)(dtp) is the only complex species present in solution. The analysis of the EPR spectra recorded after photo-irradiation in aerated acetone solutions enables the characterization of the intermediate paramagnetic species and provides a reasonable explanation.     

Fullerene polypyridine ligands: synthesis, ruthenium complexes, and electrochemical and photophysical properties

Fullerene coordination ligands bearing one bipyridine or terpyridine unit were synthesized, and their coordination to ruthenium(II) formed linear rod-like donor-acceptor systems. Steady-state fluorescence of [Ru(bpy)(2)(bpy-C(60))](2+) showed a rapid solvent-dependent, intramolecular quenching of the ruthenium(II) MLCT excited state. Time-resolved flash photolysis in CH(3)CN revealed characteristic transient absorption changes that have been ascribed to the formation of the C(60) triplet state, suggesting that photoexcitation of [Ru(bpy)(2)(bpy-C(60))](2+) results in a rapid intramolecular transduction of triplet excited state energy. The electrochemical studies on both [Ru(bpy)(2)(bpy-C(60))](2+) and [Ru(tpy)(tpy-C(60))](2+) indicated electronic coupling between the metal center and the fullerene core.     

Implementation of a Hamiliton-receptor-based hydrogen-bonding motif toward a new electron donor-acceptor prototype: electron versus energy transfer

A new modular concept for the self-assembly of electron donor-acceptor complexes is presented that ensures (i) fine-tuning the strength of the complexation, (ii) controlling the electronic coupling to impact electron and energy transfer processes, and (iii) high solubility of the corresponding hybrid architectures. This task has been realized through developing a series of porphyrin-fullerene donor-acceptor systems held together by a Hamilton-receptor-based hydrogen-bonding motif. In this context, novel libraries of C60 monoadducts (1) containing cyanuric acid side chains and of tetraphenylporphyrin derivatives (2) involving the complementary Hamilton-receptor unit were synthesized. The association constants of the corresponding 1:1 complexes (1.2) connected by six hydrogen bonds were determined complementary by NMR and fluorescence assays. Their strength, which was found to be in the range between 3.7 x 10(3) and 7.9 x 10(5) M-1, depends on the nature of the spacers, namely, hexylene versus propylene chains. Finally, transient absorption studies revealed photoinduced electron transfer from ZnP to C60 in the corresponding 1.2 complexes, which generate radical ion pair states that are persistent well beyond the ns time scale. In the case of the analogous SnP complexes, energy instead of electron transfer was observed. This is due to the shift of oxidation potential caused by presence of Sn in the oxidation state of +4.