We report here our recent studies on the ultrafast intramolecular charge transfer dynamics in cations of 2-phenylethyl-N,N-dimethylamine (PENNA) and its non-methylated counterpart, 2-phenylethylamine (PEA) after photoionization using the femtosecond pump-probe photoionization-photofragmentation (fs-PIPF) spectroscopy. Both molecules contain a phenyl and an amine groups connected by a saturated hydrocarbon bridge (-CH2-CH2-). The local ionization energy (IE) of the phenyl ring is higher than that of the amine group by about 0.7 eV in PENNA, whereas the local IE’s of the two groups are about equal in PEA. We photoionized PENNA (or PEA) in a supersonic beam with fs pump pulses at 265.9 nm with 1+1 REMPI via its S1 origin using the phenyl group as the chromophor, producing PENNA (or PEA) cation predominately in its first excited state (D1). The resulting PENNA (or PEA) cations were then probed by a second fs pulse at ~798 nm by exciting the evolving ionic system to higher excited states and thereby enhancing the fragmentation yield of the cation. The ionic dynamics was followed by monitoring the depletion of the PENNA (or PEA) parent ion as well as the formation of major fragment ion signal as a function of pump-probe delay time. The parent ion transients exhibit depletion signals with decay time constants of about 8 ps and 20 ps for PEA and PENNA cations, respectively. The observed temporal evolutions are attributed to internal conversion from the initially ionized state D1 to the ground state D0, corresponding to an electron transfer from the amine to the phenyl site, or equivalently a hole transfer from the phenyl to the amine site.

Femtosecond ion chemistry: Ultrafast intramolecular charge transfer in bifunctional molecular cations after photoionization

256th National Meeting (2018)

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