Organometallic Complexes for Nonlinear Optics. 24. Reversible Electrochemical Switching of Nonlinear Absorption

The molecular inorganic compounds 1,3,5-{trans-[RuCl(dppe)2]C⋮C-4-C6H4C⋮C}3C6H3 (1), trans-[Ru(C⋮C-4-C6H4C⋮CPh)Cl(dppe)2] (2), and trans-[Ru(C⋮CPh)Cl(dppm)2] (3) exhibit reversible oxidation in solution, assigned to the metal-centered RuII/III processes. Complexes 1−3 are essentially transparent at frequencies below 20 × 103 cm-1, whereas the green complexes 1 + −3 + have a strong absorption band centered near 11−12 × 103 cm-1. These absorption bands have been utilized to demonstrate facile NLO switching utilizing an optically transparent thin-layer electrochemical cell, a procedure which has applicability to evaluating the switching capability of a range of materials. This procedure has been applied to switch cubic nonlinearities, the first electrochromic switching of molecular nonlinear absorption. Oxidation of the molecules results in changes, including changes of sign, of both the imaginary (absorptive) part of the third-order nonlinearity and the real (refractive) part. Cycling between the two forms of the molecules is facile. The sign of the nonlinearity is reversed on oxidation of 1 and 2, whereas 3, a complex with negligible third-order nonlinearity in the resting state, has third-order nonlinearity switched on upon oxidation to 3 + .