IR/UV spectroscopy on jet cooled 3-hydroxyflavone (H2O)n (n=1,2) clusters along proton transfer coordinates in the electronic ground and excited states

Abstract

The structure and reactivity of isolated 3-hydroxyflavone (3-HF) aggregates with one and two water molecules has been investigated by applying combined infrared/ultraviolet (IR/UV) spectroscopy in a supersonic jet both for the electronic ground and excited states. In combination with density functional theory (DFT) calculations, the IR spectra of the S(0) states recorded from the upper fingerprint region to the OH stretching vibrations are assigned to the most stable isomers of the clusters. For the first electronically excited (pi pi(*)) state of the 3-HF(H(2)O)(2) cluster structural information are obtained from the IR spectra in combination with time-dependent-DFT (TD-DFT) calculations. No proton transfer structure is observed in the case of a low excess energy within the electronically excited state. By raising the excitation energy, additional bands appear that can be assigned to a tautomeric form indicating the induction of a proton transfer reaction.

Structure of Isolated Xanthone in the T1 State Obtained via Combined UV/IR Spectroscopy

“…These experimentally obtained vibrational transitions fit excellently to the calculated frequencies of xanthone in the T 1 state (DFT/B3LYP/TZVP, scaled by 0.99, [9,10,49] Figure 4 b). The transitions can be assigned to combined CC stretching (ring deformation vibrations) and CÀH bending modes.…”

“…To investigate structures of the electronic ground state, the IR photon arrives prior to an UV laser photon that excites the molecule to an energetically higher singlet state. [1][2][3][4][5] With variants of this technique, that is, by firing the IR laser after the first UV laser, the IR spectrum of electronically excited singlet states can also be recorded, [6][7][8][9][10] for example, as a depletion of the R2PI signal. Recently we have also shown that combined nanosecond UV/IR/UV spectroscopy in molecular beam experiments in combination with ab initio calculations yield structural information on isolated molecules and clusters in the electronically excited state subsequent to a proton transfer reaction.…”

“…Recently we have also shown that combined nanosecond UV/IR/UV spectroscopy in molecular beam experiments in combination with ab initio calculations yield structural information on isolated molecules and clusters in the electronically excited state subsequent to a proton transfer reaction. [9,10] However, photoinduced reactions often not only involve singlet, but also triplet states. Herein, we show that triplet states of isolated molecules can be investigated by combined ns UV/IR/UV (IR/R2PI) spectroscopy.…”

“…It is interesting to note that this value is a further hint that the ionisation starts from the T 1 state. The origin of this state is at 25 808 cm À1 [29,30] and the ionisation potential was determined by photoelectron spectroscopy in two different publications to be at 69 686 cm À1 (8,64 eV) [32] or 68 718 cm À1 (8.52 eV), [35] leading to an energy of 43 [9,10,49] cf. Figure 3 b).…”

Isolated Neutral Peptides

“…IR spectroscopy of excited states has been conducted on several biologically relevant systems [18,[216][217][218], as well as very recently on peptides [200], in order to provide a structural characterisation of the excited state. A first approach to record such spectra involves the use of a two-laser UV/IR detection scheme [18,216,217].…”