Infrared/ultraviolet quadruple resonance spectroscopy to investigate structures of electronically excited states

Abstract

Molecular beam investigations in combination with IR/UV spectroscopy offer the possibility to obtain structural information on isolated molecules and clusters. One of the demanding tasks is the discrimination of different isomers, e.g., by the use of isomer specific UV excitations. If this discrimination fails due to overlaying UV spectra of different isomers, IR/IR methods offer another possibility. Here, we present a new IR/UV/IR/UV quadruple resonance technique to distinguish between different isomers especially in the electronically excited state. Due to the IR spectra, structural changes and photochemical pathways in excited states can be assigned and identified. The method is applied to the dihydrated cluster of 3-hydroxyflavone which has been investigated as photochemically relevant system and proton wire model in the S(1) state. By applying the new IR/UV/IR/UV technique, we are able to show experimentally that both in the electronic ground (S(0)) and the electronically excited state (S(1)) two isomers have to be assigned.

Isolated Neutral Peptides

“…A detection scheme involving three sequential pulses UV/IR/UV has also been used [218], but still leads to the overlapped signature of the ground and excited states. When UV does not provide enough conformational selectivity, an IR pulse can precede the whole detection scheme to warm up the undesired conformation selectively, leading to a quadruple resonance method IR/UV/IR/UV which has been successfully applied to record a conformationselective vibrational spectrum of the S 1 excited state of a dihydrated 3-hydroxyflavone [219]. Given the size of the systems investigated, all these techniques are applicable to isolated neutral peptides [200], and should bring interesting developments in the near future.…”

Phenyl-β-D-glucopyranoside and Phenyl-β-D-galactopyranoside Dimers: Small Structural Differences but Very Different Interactions

“…Note that the only difference between both monosacharides is the relative position of the O4H hydroxyl group. such as amino acids or peptides [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], neurotransmitters [22][23][24][25][26][27][28], anesthetics [29,30], several mono-, di-and poly-saccharides [4,6,[31][32][33][34][35][36][37][38][39] or even micelles [40][41][42]. In these systems, the addition of a chromophore with an optically accessible excited electronic state is required to probe the molecules.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…Its coming into resonance with a vibrational transition of the probed species manifests itself by a depletion of this species' ground state hence a dip in the probe-induced signal. The difficulties due to accidental overlaps of S 0 -S 1 spectra of different species can be circumvented by the use of 160 A. Zehnacker multiple resonance techniques involving two or three IR lasers [123]. However, the IR-UV double-resonance techniques are limited to systems endowed with an aromatic chromophore unless VUV is used as a probe [124,125].…”