Interlayer charge-transfer in impacting the second hyperpolarizabilities: Radical and cation species of hexathiophenalenylium and its nitro dimers

Increasing nonlinear optical response: Density functional theory calculation shows that the radical dimers exhibit considerable enhancement of the second hyperpolarizabilities (γyyyy) with respect to the cation dimers. The enhancement is due to the lower transition energy and larger interlayer charge-transfer.