Electronic Spectroscopy of Protonated 1‐Aminopyrene in a Cold Ion Trap

• Published in: Chemistry, an Asian journal Vol. 12; no. 13; pp. 1523 - 1531
• Main Authors: Noble, Jennifer Anna, Dedonder‐Lardeux, Claude, Mascetti, Joëlle, Jouvet, Christophe
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 04.07.2017
• Subjects: ab initio calculations; Aromatic compounds; Carbon; Charge transfer; Chemistry; Cold traps; Decay rate; electronic spectroscopy; Fragmentation; ion trap; Ionization potentials; Ions; nitrogen heterocycles; Protonation; Spectrum analysis; Tautomers; electronic spectroscopy; ion trap; protonation; ab initio calculations; nitrogen heterocycles
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201700327

In aromatic systems that contain an amino group, there is competition between protonation on a carbon atom of the skeleton and protonation on the amino group. Herein, we studied the photofragmentation of protonated 1‐aminopyrene in a cold ion trap and mainly observed the protonated amino tautomer, which led to fragmentation pathways through the loss of H or NH3 groups. Several excited states were assigned, among which the fourth excited state showed broadened bands, thus indicating a fast decay that was attributed to the presence of a πσ* charge‐transfer state by comparison of the experimental results with ab initio calculations. We deduced the πσ* transition energies in protonated aromatic amino compounds of increasing size directly from the ionization potentials of the neutral aromatic unsubstituted molecules. Tautomers that were protonated on a carbon atom of the pyrene skeleton were also weakly observed, and we showed that two tautomers that were protonated on a carbon atom of the aromatic ring could be distinguished by using electronic spectroscopy. Caught in a trap: The photofragmentation of protonated 1‐aminopyrene was studied in a cold ion trap and the protonated amino tautomer was predominantly observed, which led to fragmentation pathways through the loss of H or NH3 groups. Fast decay was attributed to the presence of a πσ* charge‐transfer state by comparison of the experimental results with ab initio calculations.