Synthesis and Functional Control of Near-infrared Electrochromic Molecules Based on Redox-active Para-quinodimethane Scaffolds

In recent years, near-infrared (NIR) dyes, exhibiting absorption in the NIR region (750-2500 nm), has been applied to various optical applications such as security marking, photovoltaic cells and chemotherapy of deep tissues in vivo. Electrochromic systems capable of switching NIR absorption are attractive from the viewpoint of applications for material and life science, and thus several examples have been reported to date. The development of organic-based materials is needed to reduce the environmental impact and improve biocompatibility. However, since the redox states of organic NIR dyes are generally unstable, the switching of NIR absorption based on quantitative redox interconversion is still a challenging issue regarding reversibility and durability during their interconversion. To construct organic electrochromic systems capable of ON/OFF switching of NIR-absorbing properties, we have focused on the non-aromatic π-conjugated para-quinodimethane (p-QD) skeleton. Herein, we have shown several studies on the synthesis and functional control of NIR electrochromic molecules based on redox-active p-QD scaffolds. We have elucidated the spectroscopic and electrochemical properties of various arylated quinodimethane derivatives and demonstrated that p-QD building blocks can be versatile components for the development of NIR switchable organic electrochromic systems.