Femtosecond laser studies of the cis-stilbene photoisomerization reactions

Abstract

Viscosity dependence and solvent effects in the photoisomerization of cis-stilbene: Insight from a molecular dynamics study with an ab initio potential-energy function J. Chem. Phys. 111, 8987 (1999); 10.1063/1.480242 Vibrational energy redistribution and relaxation in the photoisomerization of cisstilbene J. Chem. Phys. 97, 5239 (1992); 10.1063/1.463822 Femtosecond laser study of energy disposal in the solution phase isomerization of stilbene J. Chem. Phys. 93, 9185 (1990); 10.1063/1.459707 Unimolecular reactions in isolated and collisional systems: Deuterium isotope effect in the photoisomerization of stilbeneFemtosecond laser studies have been performed on the photoisomerization reactions of cisstilbene to obtain the most detailed understanding to date of a polyatomic isomerization reaction in a condensed phase environment. These experiments demonstrate that vibrationally hot product molecules are formed within a few hundred femtoseconds of the escape of the molecule from the cis* region of the potential energy surface. Although the cis to trans reaction may proceed via a twisted intermediate structure, this intermediate is not intercepted on the -150 fs time scale. The frictional effects on the cis to trans reaction coordinate are found to be important and account for the anisotropy of the trans product molecules. Specific experiments presented in detail are the absorption spectrum of electronically excited cis molecules (cis*); the anisotropy decays for cis* showing motion along the reaction coordinate; the detection of the trans-stilbene product using transient fluorescence and transient absorption, confirming that the reaction generates hot product states and that the Franck-Condon modes are largely spectators in the reaction; the anisotropy (alignment) of trans product molecules illustrating the effect of friction coupling overall motion to the reaction coordinate; and a theoretical treatment of three-pulse anisotropy experiments.

Conformational isomers of stilbene on Si(100)

“…on opposite sides) conformation around the central bridge, for cis-or trans-stilbene, respectively. This isomerisation around the C=C-double bond can be induced by UV irradiation, as already shown in the gas phase and in solution and described theoretically [6][7][8][9]. The molecule is chemically stable against radiation over a broad wavelength range, and is in fact used as a laser-dye [10][11][12].…”

X-ray free-electron lasers

“…Much of our understanding of chemical reaction dynamics has been acquired with ultrafast optical spectroscopy [65][66][67][68][69][70][71]. Of particular significance in these time-resolved studies has been the investigation of photodissociation and recombination [66,[70][71][72][73][74][75][76][77][78][79][80], photoisomerization [69,[81][82][83][84][85][86][87][88][89][90][91][92] and photoinitiated electron transfer reactions [67,68,[93][94][95][96] at surfaces and in liquids, glasses, solids and proteins. While these extensive investigations have led to a wealth of information regarding chemical reaction dynamics in the condensed phase, critical aspects of the dynamics and the influence of the environment on chemical and biological reactions have yet to be fully characterized experimentally.…”

Proposal to DOE Basic Energy Sciences: Ultrafast X-ray science facility at the Advanced Light Source

“…Such, observations raise an important scientific question about the role of structural dynamics in influencing the reaction pathway. Recently ultrafast reactions have been described theoretically using dynamic, non Born-Oppenheimer models such as Landau-Zener tunneling [66,74], or conical intersections [75,76], which attempt to account for the role of structural (vibrational wavepacket) dynamics on the evolution of the transition state. Our present experimental understanding is limited by our inability to directly probe the molecular structure of these transition states during the course of a reaction.…”