Unexpected High Second‐Order Nonlinear Optical Activity of Metal Complexes with Three‐Branched Hexadentate 2,2′‐Bipyridine Ligands

Abstract

Two hexadentate bipyridine ligands and their RuII and NiII complexes were prepared. The helical alignment of the three electron‐donor–π‐bridge–electron‐acceptor (d‐π‐A) single‐strands with bundle architecture in cooperation with the metal center can strongly enhance the nonlinear optical (NLO) properties. The complexation of the novel cage‐type hexadentate ligands with a paramagnetic NiII‐core almost doubles the βHRS values compared with the corresponding diamagnetic RuII complexes. The hyper‐Rayleigh scattering (HRS) was performed with a highly sensitive setup for simultaneous discrimination between multi‐photon fluorescence and the molecular first hyperpolarizability.