Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.     

Synthetic enantiopure aziridinomitosenes: preparation, reactivity, and DNA alkylation studies

An enantiocontrolled route to aziridinomitosenes had been developed from l-serine methyl ester hydrochloride. The tetracyclic target ring system was assembled by an internal azomethine ylide cycloaddition reaction based on silver ion-assisted intramolecular oxazole alkylation and cyanide-induced ylide generation via a labile oxazoline intermediate (62 to 66). Other key steps include reductive detritylation of 26, methylation of the N-H aziridine 56, oxidation of the sensitive cyclohexenedione 68 to quinone 70, and carbamoylation using Fmoc-NCO. Although the aziridinomitosene tetracycle is sensitive, a range of protecting group manipulations and redox chemistry can be performed if suitable precautions are taken. A study of DNA alkylation by the first C-6,C-7-unsubstituted aziridinomitosene 11a has been carried out, and evidence for DNA cross-link formation involving nucleophilic addition to the quinone subunit is described.     

Participation of Non-Conjugated Double Bonds in Diels-Alder Reactions. A kinetic study of the addition of tropone to norbornens

A kinetic study of Diels-Alder additions between norbornene derivatives acting as dienophiles and the dienes tropone, perchlorocyclopentadiene and 9,10-dimethylanthracene is presented. The results suggest that tropone thereby acts as an electron acceptor, classifying these reactions then as Diels-Alder additions with ‘inverse electron demand’. The role of non-reacting double bonds was investigated using 7-alkylidenorbornene derivatives as dienophiles. These show comparable reactivity in ‘normal’ but enhanced reactivity in ‘inverse electron demand’ Diels-Alder additions. This outcome is interpreted in terms of frontier orbital interactions between the reactants using photoelectron spectroscopical results as a basis for the qualitative perturbation treatment. It is suggested that the enhanced reactivity in the case of the 7-alkylidene derivatives does not necessitate the consideration of a direct (‘through-space’) participation of the non-reacting double bond.     

Size-selective organization of enthalpic compatibilized nanocrystals in ternary block copolymer/particle mixtures

Dependent on the relative particle core size, two distinct types of particle topologies in block copolymer/nanocrystal blends have been identified, that is, the localization of particles along the intermaterial dividing surface or at the center of the respective polymer domain. In ternary systems consisting of block copolymer and two different-sized nanocrystal species, the distinct morphological types are conserved, resulting in autonomous size-selective separation and organization of the respective nanocrystals within alternating arrays and sheets.     

Gas‐phase functionalized carbon‐carbon coupling reactions catalyzed by Ni (II) complexes

Gas‐phase C―C coupling reactions mediated by Ni (II) complexes were studied using a linear quadrupole ion trap mass spectrometer. Ternary nickel cationic carboxylate complexes, [(phen)Ni (OOCR¹)]⁺ (where phen = 1,10‐phenanthroline), were formed by electrospray ionization. Upon collision‐induced dissociation (CID), they extrude CO₂ forming the organometallic cation [(phen)Ni(R¹)]⁺, which undergoes gas‐phase ion‐molecule reactions (IMR) with acetate esters CH₃COOR² to yield the acetate complex [(phen)Ni (OOCCH₃)]⁺ and a C―C coupling product R¹‐R². These Ni(II)/phenanthroline‐mediated coupling reactions can be performed with a variety of carbon substituents R¹ and R² (sp³, sp², or aromatic), some of them functionalized. Reaction rates do not seem to be strongly dependent on the nature of the substituents, as sp³‐sp³ or sp²‐sp² coupling reactions proceed rapidly. Experimental results are supported by density functional theory calculations, which provide insights into the energetics associated with the C―C bond coupling step.     

N-K near-edge x-ray-absorption fine structures of acetonitrile in gas phase

The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu(CN) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.     

Analysis of gas chromatography—mass spectrometry data by reverse library search and the detection of substances not in the library

Computer least-squares methods are used to conduct an automatic reverse search of a library of complete mass spectra for the analysis of the output data matrix from a g.c.—m.s. system. The search is limited to those mass spectra falling within a narrow retention index window about the retention index corresponding to each scan in the datamatrix. The least-squares estimated parameters obtained are proportional to the concentrations of the substances present at each scan and are displayed graphically as the profiles of resolved overlapping g.c. peaks. The precision of the parameters is estimated. The root mean square Values of the residuals of the least-squares fits are used successfully to indicate the presence of substances not in the library. Examples are given of the results produced with data from this laboratory. Possible elaborations and improvements of this computer program are discussed.     

Order-disorder effects of small guests in clathrates studied by nuclear quadrupole resonance and crystallography. Part I. Carbon tetrachloride and related molecules in Ni(SCN)2(3-methylpyridine)4

NQR spectroscopy and X-ray crystallography have been jointly applied to the study of the small guest molecules CH₂Cl₂, CHCl₃, CCl₄, CBr₂Cl₂, C(CH₃)2Cl₂ etc. in the Werner host complex Ni(SCN)₂(3-methylpyridine)₄. Specific host-guest dipole-dipole interactions play an important role in order-disorder effects for guest molecules in the cavities of orthorhombic system,Fddd. Thus a weakly polar molecule such as CBr₂Cl₂ exhibits a disordered alternation, both the bromine and the chlorine atoms occupying the two possible sites in theC ₂ cavity, whereas for the polar molecule C(CH₃)₂Cl₂, an ordered structure is observed. In addition, two new types of crystal structures,C2/c andP , are reported here for dichloromethane and chloroform clathrates.