Nonlinear optical properties and application of a chiral spin crossover compound

Spin crossover complexes (SCO) are well known to exhibits bistability between low-spin and high spin state. In Fe(II) compounds, it has been shown that the switching between these two spin states can be achieved at room temperature by different means [1]. This has allowed the implementation of these compounds in original devices [2, 3]. However, due to their centro-symmetry that forbids them to exhibits piezo-electric and electro-optic effect as well as second-harmonic and sum-frequency generation, their applications are still limited. In this paper, we have studied the nonlinear optical properties of chiral [Fe(phen) 3 ][Δ-As 2 (tartarate) 2 ] [Fe(phen) 3 ] [Λ-As 2 (tartarate) 2 ] SCO enantiomers of a Fe(II) we recently synthesized. We show they exhibit large second-order nonlinear optical susceptibilities and we demonstrate their use in a second-order femtosecond cross-correlator.