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Milan Gembicky

Publications and source records attributed to Milan Gembicky.

11 recordsLinked to original sources
PubMed2006

On the design of ultrafast shutters for time-resolved synchrotron experiments.

A comprehensive treatment of the limitations and possibilities for single-pulse selection in synchrotron operating modes with approximately 150 ns bunch separation, as occurs in the standard operating mode at the Advanced Photon Source, is presented. It is shown that the strength of available materials and allowable kinetic energy build-up limit single-bunch selection for this separation to sample sizes of approximately 100 microm, and that for minimization of kinetic energy build-up it is preferable to increase the r.p.m. within physically acceptable limits rather than increase the disc radius to obtain a desirable peripheral speed. A slight modification of the equal-bunch spacing standard fill patterns is proposed that allows use of samples as large as 500 microm. The corresponding peripheral speed of the chopper wheel is approximately 600 m s(-1), which is within the limits of high-strength titanium alloys. For smaller samples, peripheral speeds are proportionally lower. Versatility can be achieved with interchangeable chopper wheels and the use of different orientations of the rotation axis relative to the X-ray beam, which opens the possibility of larger, rather than one-of-a-kind, production runs.

Equipment Design↗
PubMed2006

Effect of the environment on molecular properties: synthesis, structure, and photoluminescence of Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) nanoclusters in eight different supramolecular frameworks.

By selection of different charge-balancing anionic frameworks and different host-to-guest ratios, the photosensitizer-dye cation [Cu(dmp)2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline) has been embedded in a series of three-dimensional host structures. It occurs with variable geometry in different states of aggregation, including weakly interacting monomers, isolated dimers, columns, and layers. A large variation in its emission lifetime is correlated with the relative energy level spacings of the guest- and host-framework components. In a fully saturated host framework, the lifetime exceeds values reported for a series of conventional Cu(dmp)2 salts.

Journal Article↗
PubMed2005

Carbon monoxide-promoted carbene insertion into the aryl substituent of an N-heterocyclic carbene ligand: Buchner reaction in a ruthenium carbene complex.

In the presence of carbon monoxide, ruthenium carbenes give a net insertion/ring expansion (Buchner reaction) into one of the aromatic rings of the N-heterocyclic carbene ligand. In alkene metathesis applications, the N-heterocyclic carbene ligand is both robust and typically inert to reactions with the metal-bound carbene. This unique reaction is completely regioselective. The complexes obtained through ring expansion were fully characterized in the solid state using X-ray crystallography and in solution using NMR and IR spectroscopy.

Journal Article↗
PubMed2005

A fast mechanical shutter for submicrosecond time-resolved synchrotron experiments.

A new high-speed high-repetition-rate X-ray beam shutter for time-resolved photocrystallography at synchrotron sources has been developed and tested. The new design is based on a commercially existing DC servomotor and a frequency-lock control capable linear amplifier. Accurate speed control combined with an air bearing results in extremely low jitter in the motor rotation. Measured jitter at rotation speeds of 12000 to 30000 r min-1 is less than 2 ns at a 6sigma confidence level. The chopper disc is interchangeable, allowing maximum flexibility. The chopper disc currently installed has 45 radial slots which allows synchronization from the 12th to the 20th subfrequencies of the orbit frequency of the Advanced Photon Source storage ring, corresponding to X-ray pulse frequencies of 13.6 to 22.6 kHz. At 30000 r min-1 the opening time window with a 350 microm slot size is 2.11 micros, and correspondingly less with smaller openings, which may be compared with the 3.68 micros orbit time of the Advanced Photon Source. The shutter provides high accuracy and efficient use of X-rays at a modest cost.

Journal Article↗
PubMed2005

Two novel bis(2,9-dimethyl-1,10-phenanthroline)copper(I) complexes: [Cu(dmp)2]2(PF6)2.0.5(bpmh).CH3CN and [Cu(dmp)2][N(CN)2].

Two new salts of the cation [CuI(dmp)2]+ (dmp is 2,9-dimethyl-1,10-phenanthroline, C14H12N2), namely bis[bis(2,9-dimethyl-1,10-phenanthroline-kappa2N,N')copper(I)] bis(hexafluorophosphate) hemi[bis(4-pyridylmethylidene)hydrazine] acetonitrile solvate, [Cu(C14H12N2)2]2(PF6)2.0.5C12H10N4.C2H3N or [Cu(dmp)2]2(PF6)2.0.5(bpmh).CH3CN [bpmh is bis(4-pyridylmethylidene)hydrazine, C12H10N4], (I), and bis(2,9-dimethyl-1,10-phenanthroline-2N,N')copper(I) dicyanamide, [Cu(C14H12N2)2](C2N3) or [Cu(dmp)2][N(CN)2], (II), are reported. The Cu-N bond lengths and the distortion from idealized tetrahedral geometry of the dmp ligands are discussed and compared with related compounds. The bpmh molecule in (I) is pi-pi stacked with a dmp ligand at a distance of 3.4 A, rather than coordinated to the metal atom. The molecule lies across an inversion center in the crystal. In (II), the normally coordinated dicyanamide molecule is present as an uncoordinated counter-ion.

Journal Article↗
PubMed2005

Shedding light on the structure of a photoinduced transient excimer by time-resolved diffraction.

Time-resolved single-crystal diffraction performed with synchrotron radiation shows that the 53(1) micros phosphorescent state, generated in the crystalline phase of trimeric {[3,5-(CF3)(2)Pyrazolate]Cu}(3) molecules by exposure to 355 nm of light at 17 K, is due to the formation of an excimer rather than the shortening of the intramolecular Cu...Cu distances within the trimeric units, or the formation of a continuous chain of interacting molecules. One of the intermolecular Cu...Cu distances contracts by 0.56 Angstroms from 4.018(1) to 3.46(1) Angstroms;, whereas the interplanar spacing of the trimers is reduced by 0.65 Angstroms; from 3.952(1) to 3.33(1) Angstroms. Density-functional theory calculations support the formation of a Cu...Cu bond through the intermetallic transfer of a Cu 3d electron to a molecular orbital with a large 4p contribution on the reacting Cu atoms.

Journal Article↗
PubMed2005

The structure of short-lived excited states of molecular complexes by time-resolved X-ray diffraction.

Experimental and computational methods for time-resolved (TR) diffraction now allow the determination of geometry changes on molecular excitation. The first results indicate significant changes in the interatomic distances and molecular shape on photo-excitation, but also a dependence of the induced changes on the molecular environment. Though the use of high-brightness synchrotron sources is essential, it limits the time resolution to the width of the synchrotron pulse which is currently 70-100 ps. The experiments discussed fall into two categories: (i) picosecond powder diffraction experiments on the molecular excitation to a singlet state, and (ii) microsecond experiments on the excited states of inorganic complexes. Both involve reversible processes for which a stroboscopic technique can be applied.

Journal Article↗
PubMed2004

Cu(I)(2,9-bis(trifluoromethyl)-1,10-phenanthroline)2+ complexes: correlation between solid-state structure and photoluminescent properties.

The 90K solid-state structures, room temperature absorption, and room temperature and 17 K emission spectra of seven different salts of [Cu(I)(bfp)(2)](+) (bfp = 2,9-bis(trifluoromethyl)-1,10-phenanthroline) have been determined. To quantify the distortion of the Cu coordination environment, a distortion parameter zeta is defined that is a combined measure of the flattening, rocking, and wagging distortions of the complex cations. In general, the distortion in the (bfp) cations is less than found previously for Cu(I)(dmp)(2) (dmp = 2,9-dimethyl-1,10-phenanthroline) salts, in particular the flattening is reduced because of the bulkier 2,9-substituents. The 17 K lifetimes range up to 1.8 mus in the series of solids examined and, with the marked exception of the BF(4)(-) salt, correlate linearly with the distortion parameter zeta. The emission wavelength red-shifts with decreasing lifetime, which implies that an increased ground-state distortion is associated with a smaller energy gap.

Journal Article↗
PubMed2004

Geometry changes of a Cu(I) phenanthroline complex on photoexcitation in a confining medium by time-resolved X-ray diffraction.

Using a stroboscopic technique, in which the molecule is repeatedly excited and the structural change is probed more than 5000 times per second immediately after excitation, we performed a 16 K time-resolved single-crystal study of the microsecond lifetime triplet state of the Cu(I)phenanthroline derivative[Cu(I)(dmp)(dppe)][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane). The geometry changes on excitation differ for the two symmetry-independent molecules, but are in the same direction as calculated for an isolated reference molecule, although the flattening distortion in the crystal is significantly smaller, implying that the reorganization energy is greatly affected by the confining medium.

Journal Article↗
PubMed2003

Solid-state structure dependence of the molecular distortion and spectroscopic properties of the Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) ion.

The relation between the geometry and spectroscopic properties of a series of salts of the Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) ion, (Cu((I))(dmp)(2))(+), is explored. The distortions from the idealized D(2)(d)() geometry, which include flattening, rocking of the dmp ligands, and displacement of the Cu atoms out of the dmp planes, show considerable variation, indicating the importance of packing forces in the crystalline environment. The change in the absorption spectra upon flattening of the complex, expressed as the variation of the angle between the dmp planes, which varies from 88 degrees in the BF(4) and tosylate salts to 73 degrees in the picrate, agrees qualitatively with parallel DFT calculations. No correlation is found between ground state geometry and luminescence lifetimes, recorded both at room temperature and at 16 K. The low temperature lifetimes vary by a factor of 8 among the (Cu((I))(dmp)(2))(+) salts examined, the longest lifetime (2.4 micros at 16 K) being observed for the tosylate salt.

Journal Article↗