Jesse D. Sokolow

Binding Modes of Carboxylate- and Acetylacetonate-Linked Chromophores to Homodisperse Polyoxotitanate Nanoclusters

The binding of carboxylate- and acetylacetonate-linked chromophores to homodisperse polyoxotitanate nanoclusters with 17 Ti atoms or more are surveyed and found to be limited to chelate-bidentate and the bridging modes, the former being dominant for the acetylacetonate-linked chromophores, the latter for the carboxylate linkers. Chromophores with acetylacetonate linking groups invariably bind in the chelate mode, whereas carboxylic acid terminated chromophores more frequently are observed to have the bridging mode, with the exception of three cases in which a strong electron-donating substituent is present on two different sensitizers. The calculations for isonicotinateand nitrophenylacetylacetonate functionalized Ti17 clusters show the observed binding modes to correspond to the lower energy functionalized clusters, but do not predict the difference between the cinnamic acid and dimethylaminocinnamic acid binding to Ti17, which are bridging and chelate respectively. Both binding modes were never observed to occur for a single chromophore, even when synthetic conditions were varied. Density of state calculations show broadening and splitting of the chromophore LUMO on complexation due to interaction with the clusters conduction band, as well as frequent penetration of sensitizer orbitals into the bandgap of the functionalized nanoparticle.

The development of Laue techniques for single-pulse diffraction of chemical complexes: time-resolved Laue diffraction on a binuclear rhodium metal-organic complex

A modified Laue method is shown to produce excited-state structures at atomic resolution of a quality competitive with those from monochromatic experiments. The much faster data collection allows the use of only one or a few X-ray pulses per data frame, which minimizes crystal damage caused by laser exposure of the samples and optimizes the attainable time resolution. The method has been applied to crystals of the α-modification of Rh(2)(μ-PNP)(2)(PNP)(2) (BPh(4))(2) [PNP = CH(3)N(P(OCH(3))(2))(2), Ph = phenyl]. The experimental results show a shortening of the Rh-Rh distance in the organometallic complex of 0.136 (8) Å on excitation and are quantitatively supported by quantum-mechanical (QM)/molecular-mechanics (MM) theoretical calculations which take into account the confining effect of the crystal environment, but not by theoretical results on the isolated complex, demonstrating the defining effect of the crystal matrix.

On the Biexponential Decay of the Photoluminescence of the Two Crystallographically-Independent Molecules in Crystals of [Cu(I)(phen)(PPh3)2][BF4]

[Cu(I)(phen)(PPh3)2][BF4] crystallizes with two nonsymmetry-related molecules in the asymmetric unit. Synchrotron time-resolved X-ray diffraction experiments have shown that the two independent molecules distort differently on MLCT excitation. The luminescence decay of the crystals is biexponential with two different Stokes-shifts, the more rapid decay corresponding to the shorter wavelength emission. Its amplitude diminishes rapidly with an increase in temperature, indicating that this emission is not due to a thermal activation to a higher state. The double emission is attributed to the presence of two independent molecules with drastically different packing environments. It is concluded that the solid-state environment must be analyzed whenever photochemical properties of molecular solids are reported.

Time-resolved Laue diffraction of excited species at atomic resolution: 100 ps single-pulse diffraction of the excited state of the organometallic complex Rh2(μ-PNP)2(PNP)2·BPh4

The polychromatic Laue technique has been applied in 100 ps delay synchrotron pump-probe experiments of the triplet excited state of a Rh(I) dinuclear complex. The observed contraction of the Rh-Rh distance of 0.154 (13) Å is less than predicted by a series of theoretical calculations, a difference attributed to the constraining effect of the crystal lattice.

Direct observation of the binding mode of the phosphonate anchor to nanosized polyoxotitanate clusters.

The structures of three newly synthesized phosphonate-substituted polyoxotitanates are reported. The Ti/O core of [Ti4O(OEt)12(PhenylPO3)] (1) is the building block for two larger phosphonate-substituted nanoclusters, [Ti25O26(OEt)36(PhenylPO3)6] (2) and [Ti26O26(OEt)39(PhenylPO3)6]Br (3). All compounds exhibit a not previously recognized triply bridging binding mode of the phosphonate anchor with short connecting Ti-O bonds, the average of which is 2.010(7) Å. Comparison with previously reported work suggests that the binding mode of the phosphonate anchor is strongly dependent on the structure of the underlying substrate.

Nanosized alkali-metal-doped ethoxotitanate clusters.

The synthesis and crystallographic characterization of alkali-metal-doped ethoxotitanate clusters with 28 and 29 Ti atoms as well as a new dopant-free Ti28 cluster are presented. The light-metal-doped polyoxotitanate clusters in which the alkali-metal atom is the critical structure-determining component are the largest synthesized so far. Calculations show that doping with light alkali atoms narrows the band gap compared with the nondoped crystals but does not introduce additional energy levels within the band gap.

Shedding Light on the Photochemistry of Coinage-Metal Phosphorescent Materials: A Time-Resolved Laue Diffraction Study of an AgI–CuI Tetranuclear Complex

The triplet excited state of a new crystalline form of a tetranuclear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag(I) and Cu(I) metal centers has been explored using the Laue pump-probe technique with ≈80 ps time resolution. The relatively short lifetime of 1 μs is accompanied by significant photoinduced structural changes, as large as the Ag1···Cu2 distance shortening by 0.59(3) Å. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag···Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag···Ag interaction, mainly occurring from the methylindole ligands to the silver metal centers. QM/MM optimizations of the ground and excited states of the complex support the experimental results. Comparison with isolated molecule optimizations demonstrates the restricting effect of the crystalline matrix on photoinduced distortions. The work represents the first time-resolved Laue diffraction study of a heteronuclear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.

A manganese-doped polymeric framework of polyoxotitanate nanoclusters with a narrow band gap.

A three-dimensional coordination polymer based on a manganese-doped polyoxotitanate nanocluster, {Ti13Mn4O16[MeC(CH2O)3]4(OEt)12Br4}∞, has been synthesized under solvothermal conditions. It is the first framework of doped polyoxotitanate nanoclusters reported in the literature. Compared with anatase, its band gap is reduced from 3.19 to 2.57 eV.

Analysis of multicrystal pump-probe data sets. II. Scaling of ratio data sets.

Two methods for scaling of multicrystal data collected in time-resolved photocrystallography experiments are discussed. The WLS method is based on a weighted least-squares refinement of laser-ON/laser-OFF intensity ratios. The other, previously applied, is based on the average absolute system response to light exposure. A more advanced application of these methods for scaling within a data set, necessary because of frequent anisotropy of light absorption in crystalline samples, is proposed. The methods are applied to recently collected synchrotron data on the tetra-nuclear compound Ag2Cu2L4 with L = 2-diphenylphosphino-3-methylindole. A statistical analysis of the weighted least-squares refinement residual terms is performed to test the importance of the scaling procedure.