Extended Threefold‐Symmetric Second‐Harmonic‐Generation Chromophores Based on 1,3,5‐Trisubstituted Benzene Complexes

Abstract

The elongation of the π system of a donor–π–acceptor (D–π–A) chromophore has often proven to be beneficial for its nonlinear optical (NLO) activity. Against this background, different alkynyl protecting groups such as organosilyl and dicobalt hexacarbonyl functions were investigated with respect to their ability to enable the coordination of an electron-withdrawing CpRu+ fragment (Cp = cyclopentadienyl) to a threefold ethynyl-substituted benzene ring, acting as a potential 2D NLOphore, without undesired side reactions. In addition, the influence of the perpendicularly coordinated CpRu+ unit on the NLO properties was examined. The obtained organometallic triisopropylsilyl-substituted benzene ruthenium complex and the multinuclear dicobalt hexacarbonyl protected ferrocene complex were fully characterized. Owing to the problems during the purification of the trimethylsilyl-protected benzene ruthenium complex and the subsequent deprotection to the free alkyne complex, it was not possible to fully characterize those complexes. The introduction of the CpRu+ fragment was sensitive to the steric demands of the benzene substituents but beneficial for the generation of NLO activity. The first hyperpolarizabilities of the triisopropyl and dicobalt hexacarbonyl complexes were investigated by hyper-Rayleigh scattering. The molecular structures were characterized by X-ray crystallography and infrared (IR) spectroscopy. The structures and IR spectra were compared with Kohn–Sham density functional theory calculations.