Squaraine Dyes for Photovoltaic and Biomedical Applications

Squaraine dyes (SQs) are an important class of polymethine dyes with a unique reasonable‐stabilized zwitterionic structure, in which electrons are highly delocalized over the conjugated bridge. These dyes can not only be easily synthesized via a condensation, but also exhibit intense absorption and emission in the visible and near‐infrared region with excellent photochemical stability, making them attractive material candidates for many photoelectric and biomedical applications. Thus, in this review, after an introduction of SQs, the recent advances of SQs in the photovoltaic field are comprehensively summarized including dye‐sensitized solar cells, organic solar cells, and perovskite solar cells. Then, the important advances in the use of SQs as the biosensors, biological imaging, and photodynamic/photothermal therapy reagents in the biomedical field are also discussed. Finally, a summary and outlook will be provided with some new perspectives for the future design of SQs. Squaraine dyes (SQs) are a promising class of organic functional materials with facile synthesis, unique molecular structures, and excellent optoelectronic properties. This review focuses on discussing molecular design principles that allow SQs to be applied in photovoltaic devices and as biosensors, bioimaging, and phototherapy reagents. Moreover, a perspective of the further opportunities and challenges for SQs is also presented.