Dmitry S. Yufit

Towards an understanding of structure–property relationships in hole-transport materials: The influence of molecular conformation on oxidation potential in poly(aryl)amines

The influence of molecular conformation on the oxidation (ionisation) potential and electronic structure associated with several TPD-style hole transport materials has been assessed through a combination of single crystal X-ray diffraction, electrochemical and spectroelectrochemical methods and DFT calculations. The introduction of methyl groups can be used to tune the ionisation potential of these molecular species through a combination of electronic (inductive) and thermodynamic effects, while the conformation of the biphenyl portion of the molecular framework is found to play the greatest role in determining the Marcus-type reorganisation energy associated with the charge transport process on the molecular level.

Ruthenium-catalyzed hydroarylations of methylenecyclopropanes: mild C-H bond functionalizations with conservation of cyclopropane rings.

Ring conservation was observed in the first catalytic intermolecular hydroarylation of methylenecyclopropanes via C-H bond functionalization, a remarkable reactivity mode for a transformation proceeding through (cyclopropylcarbinyl)metal intermediates.

Photoluminescent Thermometer Based on a Phase-Transition Lanthanide Silicate with Unusual Structural Disorder

The hydrothermal synthesis of the novel Na[LnSiO4] (Ln = Gd, Eu, Tb) disordered orthorhombic system is reported. At 100 K, and above, these materials are best described in the centrosymmetric orthorhombic Pnma space group. At lower temperatures (structure solved at 30 K) the unit cell changes to body-centered with Imma symmetry. The materials exhibit unique photophysical properties, arising from both, this phase transformation, and the disorder of the Ln(3+) ions, located at a site with D2d point symmetry. Na[(Gd0.8Eu0.1Tb0.1)SiO4] is an unprecedented case of a luminescent ratiometric thermometer based on a very stable silicate matrix. Moreover, it is the first example of an optical thermometer whose performance (viz., excellent sensitivity at cryogenic temperatures <100 K) is determined mainly by a structural transition, opening up new opportunities for designing such devices.

Transition metal alkynyl complexes by transmetallation from Au(CCAr)(PPh3) (Ar = C6H5 or C6H4Me-4)

Facile acetylide transfer reactions take place between gold(I) complexes Au(CCAr)(PPh3) (Ar = C6H5 or C6H4Me-4) and a variety of representative inorganic and organometallic complexes MXLn (M = metal, X = halide, Ln = supporting ligands) featuring metals from groups 8–11, to afford the corresponding metal–alkynyl complexes M(CCR)Ln in modest to good yield. Reaction products have been characterised by spectroscopic methods, and molecular structure determinations are reported for Fe(CCC6H4Me-4)(dppe)Cp, Ru(CCC6H4Me-4)(dppe)Cp*, Ru(CCC6F5)(η2-O2)(PPh3)Cp*, Ir(CCC6H4Me-4)(η2-O2)(CO)(PPh3)2, Ni(CCC6H4Me-4)(PPh3)Cp and trans-Pt(CCAr)2L2 (Ar = C6H5, L = PPh3; Ar = C6H4Me-4, L = PPh3, PMe3).

Simplifying the conductance profiles of molecular junctions: the use of the trimethylsilylethynyl moiety as a molecule–gold contact

Conductance across a metal|molecule|metal junction is strongly influenced by the molecule-substrate contacts, and for a given molecular structure, multiple conductance values are frequently observed and ascribed to distinct binding modes of the contact at each of the molecular termini. Conjugated molecules containing a trimethylsilylethynyl terminus, -C≡CSiMe(3) give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites.

Isostructural series of nine-coordinate chiral lanthanide complexes based on triazacyclononane.

Nonadentate ligands based on triazacyclononane incorporating pyridyl-2-phosphinate groups form an isostructural series of complexes with Ln ions in the solid state and in solution. The Ln ion is effectively shielded from the solvent environment. Crystal structures reveal a rigid C(3)-symmetric tricapped trigonal-prismatic coordination geometry that is maintained in solution for the methyl and phenylphosphinate series, as shown by multinuclear NMR analysis. Variable-temperature measurements of the field dependence of the water proton relaxivity in gadolinium complexes indicate that these systems exclude solvent from the primary coordination environment and minimize the second sphere of solvation. The electronic relaxation time for the gadolinium methylphosphinate complex has been estimated to be 550 (±150) ps by EPR and NMR methods, compared to values of around 0.30-0.05 ps for the terbium-ytterbium series, deduced by analyzing the field dependence (4.7-16.5 T) of the (31)P NMR longitudinal relaxation times. Values are compared with analogous azacarboxylate ligand complexes, supporting a key role for donor atom polarizability in determining the electronic relaxation. Spectral emission behavior in solution of samarium, europium, terbium, and dysprosium complexes is compared, and the resolved RRR-Λ and SSS-Δ complexes show strong circularly polarized luminescence. The molecular quadratic hyperpolarizability 〈β(HLS)〉 has been measured in solution using hyper-Raleigh light-scattering methods, for the whole series of lanthanide complexes of one ligand. The values of 〈β(HLS)〉 reach a maximum around the center of the series and are not simply dependent on the number of f electrons, suggesting a dominant contribution from the octupolar rather than the dipolar term.

The molecular structures and electrochemical response of “twisted” tetra(aryl)benzidenes

The compounds N,N,N′,N′-tetra(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (4), N,N,N′,N′-tetra(4-methylphenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5a) and N,N,N′,N′-tetra(4-methylphenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6a) undergo two reversible one electron oxidations. The first oxidation potential increases in the order 4 < 5a < 6a, while the separation between the first and second oxidation decreases in the reverse order 4 (0.30 V) > 5a (0.16 V) > 6a (0.00 V), reflecting the decreasing thermodynamic stability of the radical cations [4+] > [5+] > [6a+]. Electronic spectroscopy and spectroelectrochemistry (UV-Vis-NIR) confirm expectations, and the introduction of methyl groups at the 2,2′ and 6,6′ positions of the 1,1′-biphenyl moiety electronically decouple the arylamine moieties. In contrast, N,N,N′,N′-tetra(phenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5b) and N,N,N′,N′-tetra(phenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6b) give much less kinetically stable radical cations upon oxidation, which oligomerise/polymerise through the 4 positions of the N-phenyl groups via a step-growth process. The molecular and crystal structures of 4 and 6b are also reported.

Ruthenium‐Catalyzed Hydroarylation of Methylenecyclopropanes through CH Bond Cleavage: Scope and Mechanism

Intermolecular hydroarylation reactions of highly strained methylenecyclopropanes 2-phenylmethylenecyclopropane (1), 2,2-diphenylmethylenecyclopropane (2), methylenespiropentane (3), bicyclopropylidene (4), (dicyclopropylmethylene)cyclopropane (5), and benzhydrylidenecyclopropane (6) through C-H bond functionalization of 2-phenylpyridine (7 a) and other arenes with directing groups were studied. The reaction was very sensitive to the substitution on the methylenecyclopropanes. Although these transformations involved (cyclopropylcarbinyl)-metal intermediates, substrates 1 and 4 furnished anti-Markovnikov hydroarylation products with complete conservation of all cyclopropane rings in 11-93 % yield, whereas starting materials 3 and 5 were inert toward hydroarylation. Methylenecyclopropane 6 formed the products of formal hydroarylation reactions of the longest distal C-C bond in the methylenecyclopropane moiety in high yield, and hydrocarbon 2 afforded mixtures of hydroarylated products in low yields with a predominance of compounds that retained the cyclopropane unit. As byproducts, Diels-Alder cycloadducts and self-reorganization products were obtained in several cases from substrates 1-3 and 5. The structures of the most important new products have been unambiguously determined by X-ray diffraction analyses. On the basis of the results of hydroarylation experiments with isotopically labeled 7 a-[D(5)], a plausible mechanistic rationale and a catalytic cycle for these unusual ruthenium-catalyzed hydroarylation reactions have been proposed. Arene-tethered ruthenium-phosphane complex 53, either isolated from the reaction mixture or independently prepared, did not show any catalytic activity.

Refining the Interpretation of Near-Infrared Band Shapes in a Polyynediyl Molecular Wire

Spinning to improve (band) shape: A blend of theoretical and experimental work demonstrates that the rotational conformation of mixed-valence complexes influences the low-energy (NIR) transitions in such molecules. Interpretations of the NIR band shapes are presented.

Structure, resolution and chiroptical analysis of stable lanthanide complexes of a pyridylphenylphosphinate triazacyclononane ligand

Lanthanide complexes of a pyridylphenylphosphinate ligand based on triazacyclononane form an isostructural series. The C(3)-symmetric Δ and Λ complexes of Eu and Tb are strongly emissive and can be resolved by chiral HPLC; the absolute configuration of each complex has been assigned using CD and CPL measurements.