Paracyclophanes as model compounds for strongly interacting π-systems. Part 2: mono-hydroxy[2.2]paracyclophane

Abstract

The structure of the electronic ground- and first excited state of mono-hydroxy [2.2]paracyclophane (MHPC) and the S(1)← S(0) electronic transition have been investigated by resonance-enhanced multiphoton ionisation (REMPI) and by quantum chemical spin-component-scaled-approximate coupled cluster second order (SCS-CC2) computations. The origin of the S(1)← S(0) transition was located at 30,772 cm(-1) (3.815 eV) in the REMPI spectrum. The value has to be compared with a computed excitation energy of 3.79 eV. The vibrational structure of the spectrum confirms a significant geometry change upon excitation along the coordinates corresponding to twist- and shift-motions in the molecule. It gives rise to an experimentally observed progression with a fundamental of +30 cm(-1) and an inverse anharmonicity. From the experimental data a shallow potential along the twist coordinate was derived for the S(1) state. For the shift vibration a wavenumber of +91 cm(-1) was observed, while +85 cm(-1) was computed. The ionisation energy of MHPC was determined to be 7.63 ± 0.05 eV using synchrotron radiation. When compared to earlier results on the parent compound [2.2]paracyclophane and pseudo-ortho-dihydroxy[2.2]paracyclophane it can be seen that already small variations in the substitution pattern have a significant impact on the shapes of the involved potential energy surfaces leading to strong variations in ground and excited state geometries and opto-electronic properties governing the exciton transfer processes.

The Paternò–Büchi reaction: importance of triplet states in the excited-state reaction pathway

“…Furthermore, in a series of REMPI experiments on substituted [2.2]paracyclophanes, Schon et al observed extended progressions of largeamplitude vibrations involving the paracyclophane scaffold. 51,52 Those progressions are likely to be present in our PE spectra as well, however insufficient energy resolution makes them appear as a broadening of the spectra. The spectrum was fitted to a biexponential decay with time constants of 130 AE 20 fs and 1.7 AE 0.2 ps as well as a constant offset component, which represents a signal that lives indefinitely on the time scale of our experiment.…”

Resonant two-photon mass-analyzed threshold ionization spectroscopy of 1-fluoronaphthalene and 2-fluoronaphthalene

“…In contrast, the resonance-enhanced multi-photon ionization (REMPI) [24,25] and MATI [18,[26][27][28] methods involve detection of ions and provide similar spectroscopic date with mass information. Recently, Zhang et al [29] pointed out that under typical supersonic jet-cooled conditions, 1FN can form clusters when irradiated by UV lasers of wavelength shorter than 315 nm.…”

Two-color resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of o-chloroanisole

“…These methods involve detection of either photons or electrons with high sensitivity and spectral resolution. In contrast, the resonance-enhanced multiphoton ionization (REMPI) [11,12] and mass-analyzed threshold ionization (MATI) [13][14][15] techniques are subject to detection of ions and can also be used to obtain the same experimental data. We adopted the latter methods which provide mass information and are suitable for studies of molecular isotopomers, free radicals, complexes, and clusters.…”