Note from the author: I would like to thank the triphenylamine community for citing this old paper whenever the structure of triphenylamine is mentioned. Many thanks!

Effect of ionization by oxidation and protonation

The effect of ionization by oxidation and protonation on the structure and IR spectrum of isolated, gas-phase triphenylamine (TPA) has been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy in the fingerprint range from 600 cm−1 to 1800 cm−1 using an infrared free electron laser. IR spectra calculated using density functional theory (DFT) convincingly reproduce the experimental data. Spectral and structural differences are identified among neutral TPA, TPA+ and protonated TPA and qualitatively related to effects of resonance delocalization. As a consequence of electron delocalization, computed structural parameters for TPA remain virtually unchanged upon removal of an electron. Nonetheless, CC and CN stretching vibrations in the IR spectra of TPA+ undergo a red shift of up to 52 cm−1 as compared to those in TPA. Since ionization also strongly influences the relative band intensities, a vibrational projection analysis was used to correlate vibrational modes of TPA with those of TPA+. The experimental IR spectrum of gas-phase protonated TPA indicates that protonation occurs on the nitrogen atom, despite delocalization of the lone electron pair. Upon protonation, the structure changes from the nearly planar geometry to a near-tetrahedral configuration.

Publication: M. U. Munshi, G, Berden, J. Martens, J. Oomens, Gas-phase vibrational spectroscopy of triphenylamine: the effect of charge on structure and spectra, Physical Chemistry Chemical Physics, 2017

Structure of Triphenylamine: rotational, vibrational and electronic spectroscopy

Introduction

If the molecule consists of parts with a well-known structure, the rotational constants of the entire molecule contain enough information to determine its structure in the gas phase. An example is triphenylamine (TPA), a molecule which consists of a nitrogen atom with three phenyl groups attached to it. Since the structure of each phenyl group is known, there are only a few unknown parameters left, which are related to the relative orientation of the phenyl groups. Therefore, it is possible to determine the structure of the entire molecule. Additionally, the shape of the rotational resolved spectrum directly provides the symmetry of the molecule: TPA has a 3 fold rotational symmetry!

Triphenylamine and its Van der Waals Complexes

Both vibrationally and rotationally resolved spectra of the S1 <-- S0 transition in jet-cooled triphenylamine (TPA) around 340-320 nm are reported. Medium resolution spectra (0.5-1.0 cm-1 resolution) are recorded using (1+1)-Resonance Enhanced Multi Photon Ionization (REMPI) with mass selective Time-Of-Flight (TOF) detection in a pulsed molecular beam apparatus. The origin of the S1 <-- S0 transition is at 29520.7 cm-1, higher than halfway to the ionization potential (IP) found at 6.89 eV. A vibrational progression in the symmetric torsion mode (114 cm-1) as well as in the symmetric C--N stretching mode (280 cm-1) is observed in the electronic spectra. The spectrum of the most abundant isomer of the TPA--Ar (TPA--Kr) complexes is blue-shifted by 211 cm-1 (216 cm-1) with respect to the spectrum of the free TPA molecule. High resolution spectra are recorded using Laser Induced Fluorescence (LIF) in a cw molecular beam apparatus. Individual rotational transitions are resolved and the spectrum shows unambiguously that TPA is a symmetric top molecule. The spectrum of the blue-shifted TPA--Ar isomer is the spectrum of a symmetric top molecule as well, and therefore the Ar atom has to be located on the C3 symmetry axis, either on top of or underneath the umbrella formed by the phenyl rings. It appears that when Ar or Kr forms a complex with TPA, the first Ar, Kr, atom goes preferentially in a position on the C3 symmetry axis of TPA, a position which causes an abnormal blue-shift of the spectrum. With the first rare gas atom located in this special position, the second rare gas atom is forced into a `normal' position, i.e. above one of the phenyl-rings, causing a normal red-shift with respect to the TPA--Ar complex.

These articles may be downloaded for personal use only. Any other use requires prior permission of the author and the publisher.

Publications (pdf files)



Related papers

Structure of Triphenylamine / Giel Berden / 2025
Counts since 19/4/2006: