Efficient Near‐Infrared Fluorophores Based on Cyanostyrene Derivatives for Two‐Photon Fluorescence Bioimaging

Abstract Organic fluorescent materials with red/near‐infrared (NIR) emission are highly promising for use in biotechnology due to their exceptional advantages. However, traditional red/NIR fluorophores often exhibit weak emission at high concentrations or in an aggregated state due to the aggregate‐caused quenching effect, which severely limits their applicability in biological imaging. To address this challenge, we developed a series of cyanostyrene derivatives with aggregation‐induced emission characteristics, including 2,3‐Bis‐(4‐styryl‐phenyl)‐but‐2‐enedinitrile (DPB), 2,3‐Bis‐{4‐[2‐(4‐methoxy‐ phenyl)‐vinyl]‐phenyl}‐but‐2‐enedinitrile (DOB), 2,3‐Bis‐{4‐[2‐(4‐diphenylamino‐ phenyl)‐vinyl]‐phenyl}‐but‐2‐enedinitrile (DTB), and 2,3‐Bis‐[4‐(2‐{4‐[phenyl‐ (4‐triphenylvinyl‐phenyl)‐amino]‐phenyl}‐vinyl)‐ phenyl]‐but‐2‐enedinitrile (DTTB). Notably, these compounds exhibited intense solid state fluorescence owing to AIE effect, especially DTTB shows NIR emission with high solid state quantum efficiency (712 nm, Φ F =14.2 %). Then we prepared DTTB@PS‐PEG NPs nanoparticles by encapsulating DTTB with the amphiphilic polymer polystyrene‐polyethylene glycol (PS‐PEG). Importantly, DTTB@PS‐PEG NPs exhibited highly efficient NIR luminescence (Φ F =28.7 %) and a large two‐photon absorption cross‐section (1900 GM) under 800 nm laser excitation. The bright two‐photon fluorescence of DTTB@PS‐PEG indicated that it can be a highly promising candidate for two‐photon fluorescence probe. Therefore, this work provides valuable insights for the design of highly efficient and NIR‐emitting two‐photon fluorescent probes.