Control of charge migration in molecules by ultrashort laser pulses

Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme to control the charge-migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and amine moieties that simple pulses can be used to stop the charge-migration oscillations and localize the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

Figure 1

Ground and first excited cationic states of the molecule MePeNNA computed using the ab initio many-body Green's function ADC(3) method [22]. The next ionic state is located at 10.5 eV. The spectral intensity is defined as the combined weight of the one-hole configurations in the expansion of the ionic state and is a quantity directly related to the ionization cross section [23]. The contributions of the 1h configuration ${\left(\mathrm{HOMO}\right)}^{-1}$ are given in red (lower part of the states), while those of ${\left(\mathrm{HOMO}\text{−}1\right)}^{-1}$ are shown in green (upper part of the states). The two molecular orbitals localized on the chromophore and the amine moieties of the molecule, respectively, are also depicted. The figure is adapted from Ref. [20].

Figure 2

Time evolution of the hole density, Eq. (6), along the molecular axis of the molecule MePeNNA, after an initial localized ionization of the chromophore, controlled with a laser pulse (shown on the right) centered at 15 fs. The molecular axis is chosen to pass through the longest spatial extension of the molecule. Upper panel: The laser pulse is designed to achieve localization of the charge on the chromophore. Lower panel: The laser pulse is designed to achieve localization of the charge on the amine site.