Electro-optical response of chiral helicenes

This study demonstrates that chiral molecules in isotropic media possess a significant electro-optic response. The quantum-mechanical expression for the susceptibility contains dephasing-induced terms which are resonantly enhanced when the optical frequency corresponds to the energy difference between intermediate excited states of the chiral compound. Such dephasing-induced resonances contribute to the real part of the electro-optic susceptibility, which gives rise to absorption modulation of the optical field. The second-order electro-optic response of [7]-helicene in such a dephasing regime is estimated to be on the order of the off-resonance nonlinear susceptibility of KDP. Since, for chiral media, electroabsorption leads to modulation of the real part of the quadratic susceptibility, the optical field could in principle experience gain in the spectral domain where the dephasing terms are dominant.