Efficient Red/Near‐Infrared Fluorophores Based on Benzo[1,2‐<i>b</i>:4,5‐<i>b</i>′]dithiophene 1,1,5,5‐Tetraoxide for Targeted Photodynamic Therapy and In Vivo Two‐Photon Fluorescence Bioimaging

Abstract Red/near‐infrared dyes are highly demanded for biological applications but most of them are far from satisfactory. In this work, a series of red/near‐infrared fluorophores based on electron‐withdrawing benzo[1,2‐ b :4,5‐ b ′]dithiophene 1,1,5,5‐tetraoxide (BDTO) are synthesized and characterized. They possess both aggregation‐induced emission, and hybridized local and charge‐transfer characteristics. Crystallographic, spectroscopic, electrochemical and computational results reveal that the oxidation of benzo[1,2‐ b :4,5‐ b ′]dithiophene to BDTO can endow the fluorophores with greatly red‐shifted emission, enhanced emission efficiency, reduced energy levels, enlarged two‐photon absorption cross section, and increased reactive oxygen species generation efficiency. The nanoparticles fabricated with a near‐infrared fluorophore TPA‐BDTO show high photostability and biocompatibility with good performance in targeted photodynamic ablation of cancer cells and two‐photon fluorescence imaging of intravital mouse brain vasculature.