An excited state dynamics driven reaction: wavelength-dependent photoisomerization quantum yields in [Ru(bpy)(dmso)].

We report the excited-state behavior of a structurally simple -sulfoxide complex, -S,S-[Ru(bpy)(dmso)], as investigated by femtosecond pump-probe spectroscopy. The results reveal that a single photon prompts phototriggered isomerization of one or both dmso ligands to yield a mixture of -S,O-[Ru(bpy)(dmso)] and -O,O-[Ru(bpy)(dmso)]. The quantum yields of isomerization of each product and relative product distribution are dependent upon the excitation wavelength, with longer wavelengths favoring the double isomerization product, -O,O-[Ru(bpy)(dmso)].

Multidimensional Electronic Spectroscopy of Photochemical Reactions.

Coherent multidimensional electronic spectroscopy can be employed to unravel various channels in molecular chemical reactions. This approach is thus not limited to analysis of energy transfer or charge transfer (i.e.

Quantum control spectroscopy of competing reaction pathways in a molecular switch.

Excitation with shaped femtosecond laser pulses is a logical extension of coherent two-dimensional (2D) spectroscopy. Here we combine quantum control and information from 2D spectroscopy to analyze the initial steps in three competing reaction pathways of an isomerizing merocyanine dye. Besides the achievement of control objectives, we show how excitation with tailored pulses can be used to retrieve photochemical information that is inaccessible or experimentally demanding to obtain with other approaches.

Photoisomerization among ring-open merocyanines. II. A computational study.

The photochemical isomerization of the trans-trans-cis to the trans-trans-trans isomer of the merocyanine form of 6-nitro BIPS, which has been studied with femtosecond transient absorption spectroscopy [S. Ruetzel, M. Diekmann, P.

Photoisomerization among ring-open merocyanines. I. Reaction dynamics and wave-packet oscillations induced by tunable femtosecond pulses.

Upon ultraviolet excitation, photochromic spiropyran compounds can be converted by a ring-opening reaction into merocyanine molecules, which in turn can form several isomers differing by cis and trans configurations in the methine bridge. Whereas the spiropyran-merocyanine conversion reaction of the nitro-substituted indolinobenzopyran 6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6-nitro BIPS) has been studied extensively in theory and experiments, little is known about photoisomerization among the merocyanine isomers. In this article, we employ femtosecond transient absorption spectroscopy with variable excitation wavelengths to investigate the excited-state dynamics of the merocyanine in acetonitrile at room temperature, where exclusively the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers contribute.

Multidimensional spectroscopy of photoreactivity.

Coherent multidimensional electronic spectroscopy is commonly used to investigate photophysical phenomena such as light harvesting in photosynthesis in which the system returns back to its ground state after energy transfer. By contrast, we introduce multidimensional spectroscopy to study ultrafast photochemical processes in which the investigated molecule changes permanently. Exemplarily, the emergence in 2D and 3D spectra of a cross-peak between reactant and product reveals the cis-trans photoisomerization of merocyanine isomers.

Tracing the steps of photoinduced chemical reactions in organic molecules by coherent two-dimensional electronic spectroscopy using triggered exchange.

We establish coherent triggered-exchange two-dimensional (TE2D) electronic spectroscopy as an expansion of pump-repump-probe transient absorption spectroscopy and uniquely elucidate the role of higher-lying electronic states in ultrafast photochemistry. As an example, this is demonstrated for a molecular switch present in two ring-open conformations. The formation of a new species-the radical cation-is observed and its precursor state is identified via TE2D.

Reaction dynamics of a molecular switch unveiled by coherent two-dimensional electronic spectroscopy.

Coherent two-dimensional electronic spectroscopy is usually employed on molecular species with fixed geometric configuration. Here we present two-dimensional Fourier-transform electronic spectra of dissolved 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro-BIPS), a photochromic system present in two ring-open forms differing in the cis/trans configuration of a double bond, which both undergo a photoinduced ring closure. The two-dimensional spectra, recorded with 20 fs pump pulses centered at 605 nm and a supercontinuum probe covering the complete visible spectral range, allow for a detailed analysis of the photophysics and photochemistry of the two isomers and directly reveal that cis/trans isomerization among them does not play a major role.

Adaptive coherent control using the von Neumann basis.

Recently we introduced the von Neumann representation as a joint time-frequency description for femtosecond laser pulses. Here we show that the von Neumann basis can be implemented into an evolutionary algorithm for adaptive optimization in coherent control. We perform simulations that demonstrate the efficiency compared to other parametrizations in the frequency domain.

Molecular quantum control landscapes in von Neumann time-frequency phase space.

Recently we introduced the von Neumann representation as a joint time-frequency description for femtosecond laser pulses and suggested its use as a basis for pulse shaping experiments. Here we use the von Neumann basis to represent multidimensional molecular control landscapes, providing insight into the molecular dynamics. We present three kinds of time-frequency phase space scanning procedures based on the von Neumann formalism: variation of intensity, time-frequency phase space position, and/or the relative phase of single subpulses.