Multiresonant coherent multidimensional vibrational spectroscopy of aromatic systems: pyridine, a model system

Multiresonant four wave mixing has been used to measure the coherent multidimensional spectroscopy (CMDS) of representative aromatic ring modes using pyridine as a model system. This work identifies the cross-peaks that appear between several modes and measures their coherent and incoherent dynamics. The work also explores the consequences of using multiresonant CMDS for molecules with transition moments that are typical of most vibrational modes. Typically, CMDS experiments rely on using transitions with exceptionally large transition moments. To observe cross-peaks, the pyridine concentration was raised until absorption effects became very important. These effects interfere with the parametric CMDS coherence pathways, but they do not make important contributions to the nonparametric pathways.     

Ab initio study of phosphorescent emitters based on rare-earth complexes with organic ligands for organic electroluminescent devices

An ab initio approach is developed for calculation of low-lying excited states in Ln(3+) complexes with organic ligands. The energies of the ground and excited states are calculated using the XMCQDPT2/CASSCF approximation; the 4f electrons of the Ln(3+) ion are included in the core, and the effects of the core electrons are described by scalar quasirelativistic 4f-in-core pseudopotentials. The geometries of the complexes in the ground and triplet excited states are fully optimized at the CASSCF level, and the resulting excited states have been found to be localized on one of the ligands. The efficiency of ligand-to-lanthanide energy transfer is assessed based on the relative energies of the triplet excited states localized on the organic ligands with respect to the receiving and emitting levels of the Ln(3+) ion. It is shown that ligand relaxation in the excited state should be properly taken into account in order to adequately describe energy transfer in the complexes. It is demonstrated that the efficiency of antenna ligands for lanthanide complexes used as phosphorescent emitters in organic light-emitting devices can be reasonably predicted using the procedure suggested in this work. Hence, the best antenna ligands can be selected in silico based on theoretical calculations of ligand-localized excited energy levels.     

Live encapsulation of a Keggin polyanion in NH2-MIL-101(Al) observed by in situ time resolved X-ray scattering

The templating effect of the Keggin polyanion derived from phosphotungstic acid (PTA) during the synthesis of NH(2)-MIL-101(Al) has been investigated by means of in situ SAXS/WAXS. Kinetic analysis and structural observations demonstrate that PTA acts as a nucleation site and that it stabilizes the precursor phase NH(2)-MOF-235(Al). Surprisingly kinetics of formation are little changed.     

Encapsulation of transition metal atoms into carbon nanotubes: a supramolecular approach

A functionalised fullerene incorporating a double-chelating group binds transition metal cations and acts as an effective vehicle for delivering metals into carbon nanotubes.     

A Covalent Organic Framework with 4 nm open pores

The synthesis and characterization of a new mesoporous Covalent Organic Framework BTP-COF is described, the latter having fully accessible pores with an open diameter of 4.0 nm.     

Semiclathrates of the Ge-P-Te system: synthesis and crystal structures

Novel compounds [Ge_46?xP_x]Te_y (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate‐like structures have been prepared and structurally characterized. They crystallize in the space group Fm$\bar 3Novel compounds [Ge(46-x) P(x) ]Te(y) (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate-like structures have been prepared and structurally characterized. They crystallize in the space group Fm ?3 with the unit cell parameter changing from 20.544(2) to 20.698(2) ? (Z=8) on going from x=13.9 to x=15.6. Their crystal structure is composed of a covalently bonded Ge-P framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type?I clathrate superstructure. In contrast to the conventional type I clathrates, [Ge(46-x) P(x) ]Te(y) contain tricoordinated (3b) atoms and no vacancies in the framework positions. As a consequence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first representative of semiclathrates with covalent bonding. A comparison is made with silicon clathrates and the evolution of the crystal structure upon changing the tellurium content is discussed.     

Assessment of dressed time-dependent density-functional theory for the low-lying valence states of 28 organic chromophores

Almost all time-dependent density-functional theory (TDDFT) calculations of excited states make use of the adiabatic approximation, which implies a frequency-independent exchange-correlation kernel that limits applications to one-hole/one-particle states. To remedy this problem, Maitra et al. [N.T. Maitra, F. Zhang, R.J. Cave, K. Burke, Double excitations within time-dependent density functional theory linear response theory, J. Chem. Phys. 120 (2004) 5932 ] proposed dressed TDDFT (D-TDDFT), which includes explicit two-hole/two-particle states by adding a frequency-dependent term to adiabatic TDDFT. This paper offers the first extensive test of D-TDDFT, and its ability to represent excitation energies in a general fashion. We present D-TDDFT excited states for 28 chromophores and compare them with the benchmark results of Schreiber et al. [M. Schreiber, M.R. Silva-Junior, S.P.A. Sauer, W. Thiel, Benchmarks for electronically excited states: CASPT2, CC2, CCSD, and CC3, J. Chem. Phys. 128 (2008) 134110]. We find the choice of functional used for the A-TDDFT step to be critical for positioning the 1h1p states with respect to the 2h2p states. We observe that D-TDDFT without HF exchange increases the error in excitations already underestimated by A-TDDFT. This problem is largely remedied by implementation of D-TDDFT including Hartree-Fock exchange.