Photoelectrochemical Hole Injection Revealed in Polyoxotitanate Nanocrystals Functionalized with Organic Adsorbates
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bio-inspired↗
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Coppens, Philip
Publications and source records attributed to Coppens, Philip.
Shedding Light on the Photochemistry of Coinage-Metal Phosphorescent Materials: A Time-Resolved Laue Diffraction Study of an Ag I -Cu I Tetranuclear Complex
The triplet excited state of a new crystalline form of a tetranuclear coordination d 10 –d 10 -type complex, Ag 2 Cu 2 L 4 (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.
Jarzembska, Katarzyna N.↗
Analysis of multicrystal pump–probe data sets. I. Expressions for the RATIO model
The RATIO method in time-resolved crystallography [Coppens et al. (2009). J. Synchrotron Rad. 16 , 226–230] was developed for use with Laue pump–probe diffraction data to avoid complex corrections due to wavelength dependence of the intensities. The application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. The assessment of the accuracy of pump–probe time-resolved structure refinements based on the observed ratios was discussed in a previous paper. In the current paper, a detailed ratio model is discussed, taking into account both geometric and thermal light-induced changes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction
We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques. The light-driven transformations in the two polymorphs are compared. Combining both techniques and tracking how the X-ray data correlate with optical signals allow understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium. The study sheds light on crossing the border between femtochemistry at the molecular scale and femtoswitching at the material scale.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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) {micro}s phosphorescent state, generated in the crystalline phase of trimeric {l_brace}[3,5-(CF{sub 3}){sub 2}Pyrazolate]Cu{r_brace}{sub 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 {angstrom} from 4.018(1) to 3.46(1) {angstrom}, whereas the interplanar spacing of the trimers is reduced by 0.65 {angstrom} from 3.952(1) to 3.33(1) {angstrom}. 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.
43 PARTICLE ACCELERATORS↗
On the refinement of time-resolved diffraction data: comparison of the random-distribution and cluster-formation models and analysis of the light-induced increase in the atomic displacement parameters
Expressions for the random-distribution and cluster-formation models for light-induced changes in crystals studied by time-resolved diffraction are presented. The two models can be distinguished on the basis of differences in the predicted intensities. The light-induced increase in the atomic displacement parameters is analyzed with both simulated and experimental data sets.
43 PARTICLE ACCELERATORS↗
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 12,000 to 30,000 r min{sup -1} is less than 2 ns at a 6{sigma} 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{sup -1} the opening time window with a 350 {micro}m slot size is 2.11 {micro}s, and correspondingly less with smaller openings, which may be compared with the 3.68 {micro}s orbit time of the Advanced Photon Source. The shutter provides high accuracy and efficient use of X-rays at a modest cost.
43 PARTICLE ACCELERATORS↗