Third-order nonlinear optical properties of soluble Cr(Ⅲ)-dioxolene complexes

摘要

We synthesized novel ligand-based mixed valence (LBMV) Cr~Ⅲ-dioxolene complexes, [Cr(X_4SQ)(X_4Cat)(4,4′-di-tert-butyl-2,2′-bpy)] (SQ = semiquinone, Cat = catecohol, 2,2′-bpy = 2,2′-bipyridine; X = Cl (2a) and Br (2b)) and [Cr(X_4SQ)(X_4Cat)(4,4′-dinonyl-2,2′-bpy)] (X = Cl (3a) and Br (3b)), and prepared thin films for investigating their third-order nonlinear optical (NLO) properties in terms of the mixed valence states. Electronic absorption spectra of these complexes in solution and solid states showed an intervalence charge-transfer (IVCT) band from Cat~(2-) to SQ~(·-) at the IR region, indicating of a coexistence of SQ and Cat ligands, namely, LBMV state of the complexes. These complexes were well soluble in nonpolar organic solvent, which allowed us to prepare thin films by spin coating. The obtained films showed the electronic absorption spectra similar to those in solution and were amorphous because of steric hindrance of halogen and alkyl substituents in o-dioxolene and 2,2′-bpy moieties, respectively. The χ~((3)) values of the films of 3a and 3b with a thickness of 30 ～ 40 nm were determined for 1.0 x 10~(-12) esu at 1.907 μm.