A circularly polarized femtosecond laser can induce electronic ring currents within a single molecule, which are expected to persist for as long as nanoseconds. Photoinduced ring currents in molecules have not yet been observed experimentally, and most theoretical studies have assumed rather weak laser intensity - below 10<sup>12</sup> W/cm<sup>2</sup>, which limits the strength of the induced current. In the present contribution we discuss results of theoretical study of excitation and coherent control of the ring current in benzene with ultrashort circularly polarized laser pulses. In order to model ring currents in benzene generated by both a weak and moderate laser intensity femtosecond laser pulses, we have used Time Dependent Density Functional Theory (TDDFT). We study the properties of the ring current over the range of laser pulse frequencies and intensities. Results of the simulations within TDDFT and comparison to Tight Binding method results are discussed in detail. TDDFT results indicate that with the increase of the laser intensity the resonance enhanced ionization influences the propeties of the persistent ring current. Interestingly depending on the peak laser intensity of the pulse, the current can predominantly be carried by either electrons or holes (Fig 1). For higher laser intensities the leading contribution from the hole current results in the change of the direction of the total ring current in the molecule. Furthermore we present how the mechanism can be used to switch between the two regimes of co- and counter propagating ring currents during the laser pulse and we discuss properties of the laser pulse neecessary to achieve such control of the ring current. Finally we discuss the application of the transient absorption spectroscopy to study temporary properties of the induced ring current.

Ultrafast control of photoinduced ring-currents in benzene

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.