Effect of π-conjugate units on the ferrocene-based complexes: Switchable second order nonlinear optics controlled by redox stimuli

The control of rotational motion, using an external impulse (such as redox), has been intensively pursued as nonlinear optics switch. Four redox responsive ferrocene-based actuators with varied pi-conjugated units have been systematically investigated by the density functional theory. The open structures of these complexes with antiparallel orientation of both pi-conjugated units are due to the large charge repulsion effect, while the closed forms are stabilized by the intramolecular pi-pi stacking interactions. The rotational motion can be triggered by reduction process preferentially centered on the pi-conjugated units. The polarizabilities and first hyperpolarizabilities of complexes [3](closed)(2+) and [4](closed)(2+) are significant enhanced, which are respectively related to the electronic spatial extent and intramolecular interlayer charge transfer occurred between two respective pi-conjugated units. Overall, the present work shows that one can design the molecular nonlinear optical switches characterized by a large contrast varying from zero to a large value along the reversible transformations. (C) 2015 Elsevier Ltd. All rights reserved.