Intervalence charge transfer transition in mixed valence complexes synthesised from Ru<SUP>III</SUP>(edta)- and Fe<SUP>II</SUP>(CN)<SUB>5</SUB>-cores

Intervalence charge transfer properties were studied for a set of mixed valence complexes incorporating Ru(III) and Fe(II)-centres linked by various saturated and unsaturated bridging ligands (BL). Studies reveal that degree of ground state electronic interaction and coupling between Ru(III) and Fe(II)-centres can be attenuated by changing the nature of the bridging ligand. Further, inclusion of the bridging ligand with interrupted π-electron system in a β-CD cavity initiate an optical electron transfer from Fe(II) to Ru(III) which is otherwise not observed

Cerium ion-induced fluorescence enhancement of a tripodal fluoroionophore

A new tripodal ligand, N-anthracen-9-ylmethyl-N',N'-bis-[2-(anthracen-9-ylmethyl-thiophen-2-ylmethylamino)ethyl]-N-thiophen-2-ylmethyl-ethane-1,2-diamine 2 was synthesized. Selective fluorescence enhancement was observed in the presence of Ce3+ for this newly synthesized ionophore in dry tetrahydrofuran (THF). A new tripodal ligand shows selective fluorescence enhancement in the presence of Ce3+

Kinetics of oxidation of ascorbic acid and 1,4-dihydroxybenzene by semiquinone radical bound to ruthenium(II)

In 40% (v/v) MeOH-H2O media, containing [H+] (0.001-0.038 mol dm-3), the semiquinone (sq) radical, bound to Ru(II) in [Ru(bpy)2(sq)]+1, oxidises ascorbic acid (H2A) to dehydroascorbic acid (A), and 1,4-dihydroxybenzene (H2Q) to p-benzoquinone (Q); 1 is itself reduced to [Ru(bpy)2(Hcat)]+2H. The reactions are centred at sq not Ru(II). The sq/cat couple in 1 is reversible and its E1/2 increases with increasing [H+]; rate of chemical reduction of 1 to 2H increases in parallel. Rate increases also with increasing mole percent of D2O in the solvent suggesting a preliminary protonation equilibrium producing 1H, in which a H+ binds to the π-electron cloud of Ru(II)-bound sq. Under the experimental conditions, the kinetically significant species are 1H, H2Q, H2A and HA-. The kinetic activity of HA- ion is only ≈200 times more than that of H2A. This testifies against a purely outer-sphere mechanism and suggests significant electronic interaction between the redox partners. Increased percentage of MeOH in the solvent decreases λmax for the LMCT band; reaction rate for ascorbic acid decreases in parallel

Electrochemical addressing of the optical properties of a monolayer on a transparent conducting substrate

The electrochemical storage of charge in a ruthenium-based monolayer on a hydrophilic substrate (eg indium-tin oxide coated glass) leads to a change in the optical properties of the system (see picture). This read / write process is performed at low voltage in air and UV / Vis spectrophotometry are pursued. This would allow the system to non-volatile memory storage may be suitable

Redox switchable NIR dye derived from ruthenium-dioxolene-porphyrin systems

Newly synthesised Ru(bp)2(sq)+-derivatives, covalently linked to a porphyrin-core, show very high ε values in the NIR region; which exhibit fast on/off switching depending on the redox state of the coordinated dioxolene functionality

Dinuclear complexes of a new bridging ligand containing 2,2'-bipyridyl and dioxolene binding sites: syntheses, electrochemical and electronic spectroscopic properties

Demethylation of the methoxy groups of 4-methyl-4'-{1-(3,4-dimethoxyphenyl)-ethen-2-yl}-2,2'-bipyridine (Me<SUB>2</SUB>L<SUP>1</SUP>) affords the new bridging ligand H<SUB>2</SUB>L<SUP>1</SUP> [4-methyl-4'-{1-(3,4-dihydroxyphenyl)-ethen-2-yl}-2,2'-bipyridine] which contains a 2,2'-bipyridyl binding site linked to a catechol binding site. The mononuclear complexes [Ru(bipy)<SUB>2</SUB>(Me<SUB>2</SUB>L<SUP>1</SUP>)][PF<SUB>6</SUB>]<SUB>2</SUB> (1) and [Ru(bipy)<SUB>2</SUB>(H<SUB>2</SUB>L<SUP>1</SUP>)][PF<SUB>6</SUB>]<SUB>2</SUB> (2), were prepared and attachment of a second metal fragment to the pendant catechol site of 2 afforded the dinuclear complexes [(bipy)<SUB>2</SUB>Ru(μ-L<SUP>1</SUP>)PdL][PF<SUB>6</SUB>]<SUB>2</SUB> (3, L = bipy; 4, L = 4,4'-<SUP>t</SUP>Bu<SUB>2</SUB>-bipy), [(bipy)<SUB>2</SUB>Ru(μ-L<SUP>1</SUP>)Pt(PPh<SUB>3</SUB>)<SUB>2</SUB>][PF<SUB>6</SUB>]<SUB>2</SUB> (5), [(bipy)<SUB>2</SUB>Ru(μ-L<SUP>1</SUP>)Ru(NO)(Cp<SUP>*</SUP>)][PF<SUB>6</SUB>]<SUB>2</SUB> (6) and [(bipy)<SUB>2</SUB>Ru(μ-L<SUP>1</SUP>)Ru(bipy)<SUB>2</SUB>][PF<SUB>6</SUB>]<SUB>3</SUB> (7). In 3-6 the coordinated dioxolene fragment is in the catechol oxidation state in each case; in 7 it has become oxidised to the semiquinone oxidation state. The dinuclear complexes show electrochemical and UV/VIS spectroscopic properties that are the sum of the component parts, with some perturbation: for example (i) 7 shows three reversible redox couples, associated with catecholate/semiquinone and semiquinone/quinone couples of the dioxolene fragment, and the Ru(II)/Ru(III) couple of the {Ru(bipy)<SUB>3</SUB>}<SUP>2+</SUP> core; (ii) the catecholate → bipy llct transitions of 3 and 4 are an order of magnitude more intense than that of the mononuclear Pd(II) complex [Pd(bipy)(cat)] (cat = catecholate dianion) alone. Whereas 1 and 2 show the characteristic luminescence of the {Ru(bipy)<SUB>3</SUB>}<SUP>2+</SUP> core, in all of the dinuclear complexes the luminescence is quenched

Dimerization of aromatic ureido pyrimidinedione derivatives: observation of an unexpected tautomer in the solid state

Ureido pyrimidinedione derivatives with phenyl, 1-naphthyl and 2-naphthyl substituents form stable dimers via quadruple hydrogen bonding, but the 1-naphthyl derivative presents an unexpected tautomer in the solid state