Electro-switching of first hyperpolarizability of metallorganic complexes via ligand reduction/oxidation

Highlights: • Enhancing molecular hyperpolarizability (β) of an organometallic complex by ligand reduction. • In situ reduction followed by second harmonic light scattering in solution yields β value. • Two-and three-state switchings of β for repeated cycles of reduction/oxidation are seen. We report electro-switching of first hyperpolarizability (β) in monometallic (1) and bimetallic (2) Re(I) complexes containing 1,2-bis(pyridine-2-yl methylene)hydrazine (pymh) ligand. Both two- and three-state switching of β have been achieved by one- and two-electron reductions of the pymh ligand using, in situ, second harmonic light scattering (SHLS) from solution. We have shown that pymh reductions lead to an increase in β and this is due to reorganization of the molecular orbital energy levels subsequent to electron injection into the ligand orbitals and appearance of ligand to metal charge transfer (LMCT) bands closer to one and two-photon resonances at experimental wavelength.