  Floquet engineering is a convenient strategy to induce nonequilibrium
phenomena in molecular and solid-state systems, or to dramatically alter the
physicochemical properties of matter, bypassing costly and time-consuming
synthetic modifications. In this article, we investigate theoretically some
interesting consequences of the fact that an originally achiral molecular
system can exhibit nonzero circular dichroism (CD) when it is driven with
elliptically polarized light. More specifically, we consider an isotropic
ensemble of small cyclic molecular aggregates in solution whose local
low-frequency vibrational modes are driven by an elliptically polarized
continuous-wave infrared pump. We attribute the origin of a nonzero CD signal
to time-reversal symmetry breaking due to an excitonic Aharonov-Bohm (AB) phase
arising from a time-varying laser electric field, together with coherent
interchromophoric exciton hopping. The obtained Floquet engineered excitonic AB
phases are far more tunable than analogous magnetically-induced electronic AB
phases in nanoscale rings, highlighting a virtually unexplored potential that
Floquet engineered AB phases have in the coherent control of molecular
processes and simultaneously introducing new analogues of magneto-optical
effects in molecular systems which bypass the use of strong magnetic fields.
