Novel near-infrared active dinuclear ruthenium complex materials: effects of substituents on optical attenuation

A series of dinuclear ruthenium complexes with 1,2-dicarbonylhydrazido (DCH) ligands having various substituents were prepared in order to study the correlation between their optical, electrochemical behaviour and the electron density within the bridging ligands. As the average donor strength of the substituent increases, the oxidation potential shifts to a lower value and the metal-to-metal charge transfer (MMCT) band shifts to a higher energy. A strong MMCT absorption in the near-infrared region makes these compounds potentially useful for optical attenuation. The intrinsic attenuation property of these materials depends mainly on the concentration of ruthenium content in the complexes. The first dendritic DCH-Ru complex was prepared and showed a strong electrochromism at around 1550 nm and a fast switching speed of less than 2 s. A variable optical attenuator device based on the crosslinked ruthenium dendrimer is demonstrated with 18 000 switching cycles.