Issue 20, 2015

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

Abstract

Femtosecond spectroscopy with hyperspectral white-light detection was used to elucidate the ultrafast primary processes of the thermodynamically stable organic radical, 1,3,5-triphenylverdazyl, in liquid acetonitrile solution at room temperature. The radical was excited with optical pulses having a duration of 39 fs and a center wavelength of 800 nm thereby accessing its energetically lowest electronically excited state (D1). The apparent spectrotemporal response is understood in terms of an ultrafast primary D1-to-D0 internal conversion that generates the electronic ground state of the radical in a highly vibrationally excited fashion within a few hundred femtoseconds. The replenished electronic ground state subsequently undergoes vibrational cooling on a time scale of a few picoseconds. The instantaneous absorption spectra of the radical derived from the femtosecond pump–probe data are analyzed within the Sulzer–Wieland formalism for calculating the electronic spectra of “hot” polyatomic molecules. The pump–probe spectra together with transient anisotropy data in the region of the D0 → D1 ground-state bleach gives evidence for an additional transient absorption that arises from a dark excited state, which gains oscillator strength with increasing vibrational excitation of the radical by virtue of vibronic coupling.

Graphical abstract: Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

Article information

Article type
Paper
Submitted
09 Mar 2015
Accepted
22 Apr 2015
First published
29 Apr 2015

Phys. Chem. Chem. Phys., 2015,17, 13659-13671

Author version available

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

C. Weinert, B. Wezisla, J. Lindner and P. Vöhringer, Phys. Chem. Chem. Phys., 2015, 17, 13659 DOI: 10.1039/C5CP01383F

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