Time-Resolved X-ray Diffraction of the Photochromic α-Styrylpyrylium Trifluoromethanesulfonate Crystal Films Reveals Ultrafast Structural Switching

Abstract

The ultrafast structural dynamics of the [2+2] photocycloaddition of alpha-styrylpyrylium trifluoromethanesulfonate (TFMS) has been studied in great detail. During the photoreaction, optical and infrared spectroscopy confirms that crystals of alpha-styrylpyrylium change color. Since the reaction is reversible, it has been suggested to be used as an organic holographic storage device. The present photocrystallographic studies (with high spatial resolution) allow for an electron density analysis of the overall reaction kinetics, revealing the mechanism of bond-breaking and bond-formation. It could furthermore be proved how the reaction is influenced by the rearrangement of the surrounding moieties. Picosecond time-resolved X-ray diffraction studies allow for the monitoring the photoreaction in crystalline thin films under experimental conditions where the transformation times are greatly enhanced. These investigations are discussed in the context of the photocrystallographic results. It has been found that alpha-styrylpyrylium TFMS undergoes an ultrafast photoreaction to the dimer product state and back-reaction to the monomer reactant state which is temperature driven. The present experiments indicate that TFMS reacts on time scales which are the fundamental limiting ones of two-quantum systems and therefore has the potential to be used as an ultrafast organic molecular switcher.

Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets

“…30,31 Since the discovery of x-rays, 32 scattering of x-rays from matter has been used to unveil the structure of molecules, solids, and biomolecules with atomic-scale spatial resolution. [33][34][35][36][37] Also, scattering of x-rays from atoms and molecules has been proposed to gain insight about the excited electronic states of atomic and molecular systems. 38,39 In order to image electronic motion in real-time and realspace with spatial and temporal resolutions of order 1 Å and 1 fs, respectively, one can perform scattering of ultrashort xray pulses from the dynamically evolving electronic charge distribution.…”

Electronic structure in real time: mapping valence electron rearrangements during chemical reactions

“…Pump-probe experiments where probing is accomplished with x-rays give unique access to the dynamics of nuclear and electronic degrees of freedom both on the atomic length scale of Å and on pico-to femtosecond time scales corresponding to nuclear motions. Ultrashort x-ray pulses have thus been used to track nuclear dynamics in solids and during chemical reactions in liquids (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35). As nuclei move during chemical reactions the electronic structure changes concomitantly and, compared to time-resolved laser techniques, time-resolved x-ray spectroscopy gives unprecedented access to this electronic structure evolution as will be demonstrated in this perspective.…”

Concentration Effects on the Dynamics of Liquid Crystalline Self-Assembly: Time-Resolved X-ray Scattering Studies

“…So far, the investigated phase transitions were either driven by laser heating or by intermediate formation following optical selection rules. 5 Photosensitization by means of dye systems extends the possibility of photo inducing phase transitions to any arbitrarily chosen matter, which might be inherently inert against optical excitation. Furthermore, photosensitization allows the initiation of phase transitions, which are driven by Stokes or anti-Stokes optical excitation resulting in a heating or cooling of the surroundings of the dye molecules.…”