Ultrafast structural dynamics of in-cage isomerization of diiodomethane in solution

Abstract

The structural dynamics of in-cage isomerization of CH2I2 and the unusual structure of the loosely-bound isomer precursor were unveiled with femtosecond X-ray liquidography (solution scattering).

Ligand-Field Effects in a Ruthenium(II) Polypyridyl Complex Probed by Femtosecond X-ray Absorption Spectroscopy

“…Time-resolved X-ray absorption spectroscopy (TR-XAS) is an element-specific method for obtaining such information, − and the development of X-ray free-electron lasers (XFELs) facilitates real-time monitoring of photoinduced processes on the natural time scales of elementary chemical reactions. − Many studies on metal complexes with femtosecond TR-XAS have revealed ultrafast excited-state relaxation processes with information on electronic and structural dynamics. − The sensitivity of X-ray transitions to transient valence charge distributions provides the trajectories of electronic excited states, such as intramolecular charge transfer, , spin crossover, ,, and isomerization involving the MLCT and MC state. On the other hand, time-resolved X-ray solution scattering (liquidography) is widely used to study the ultrafast structural dynamics due to its sensitivity to global molecular change. − The more recently coined tender X-ray regime (∼2–5 keV) includes the L-edges of 4d transition metals (e.g., Ru, ,, Rh, Pd, Ag) and K-edges of lighter elements (P, , S, − Cl) which are relevant in catalytic systems, e.g., for C–H bond activation. − For instance, at the Ru L 3 -edge, the 2p-to-4d transitions monitor the metal 4d-orbitals with clearly distinct spectroscopic signatures for charge transfer (MLCT) and optically dark MC states …”

Reaction dynamics studiedviafemtosecond X-ray liquidography at X-ray free-electron lasers

“…Similarly, a geminal radical pair of CH 2 I 2 has also been identified in the fs-TRXL study of CH 2 I 2 in methanol. 67 The geminal radical pair stems from the non-covalent interaction between CH 2 I˙ and I˙ in a solvent cage and, therefore, does not have a well-defined structure, as has been the case for the study of the radical pair of CH 2 I 2 in cyclohexane. This structural feature has been further confirmed by the unusually large σ 2 value of the DWF for the I⋯I distances of the radical pair of CH 2 I 2 , which is contrary to the final photoisomer, CH 2 I–I, whose σ 2 for the I–I bond length was a typical small value of a well-defined atomic pair distance.…”

Sensitivity of time‐resolved diffraction data to changes in internuclear distances and atomic positions

“…23,59 (c) CH 2 I 2 !CH 2 I + I in methanol. 60,75 (d) C 2 H 4 I 2 !bridged-C 2 H 4 I + I in cyclohexane. 7,33 (e) C 2 F 4 I 2 !anti-C 2 F 4 I + I in cyclohexane.…”

“…Thus, analyzing the scattering pattern can unveil the structural information, [87][88] and analyzing the time-resolved scattering patterns can unveil the timedependent structural changes of molecules. A TRXL experiment is conducted at a beamline of a synchrotron or an x-ray free-electron laser (XFEL), [67][68][69][70][71][72][73][74][75][76][89][90] which provides x-ray pulses with a pulse width of $100 ps and $100 fs, respectively. Generally, beamtimes are offered based on competitive selection procedures of research proposals.…”