Tuning Molecular Packing by Twisting Structure to Facilely Construct Highly Efficient Solid‐State Fluorophores for Two‐Photon Bioimaging and Photodynamic Therapy

Abstract The traditional design strategy for constructing highly bright solid‐state luminescent materials relies on incorporating aggregation‐induced emission (AIE) scaffolds, molecular rotors, or bulky substituents to prevent close cofacial packing, which limits the strategy diversity in developing new materials. Herein, a strategy of tuning molecular packing by twisting molecular structure of conventional aggregation‐caused quenching fluorophore is proposed to endow materials with AIE effect and enhance the solid‐state fluorescence. Accordingly, a series of 1,4‐bis(diphenylamino)‐2,5‐disubstituted benzene fluorophores exhibiting AIE characteristics, high solid‐state fluorescence efficiency (up to 0.99), wide emission color tunability, and good near‐infrared (NIR) two‐photon absorption is facilely developed. All these luminogens can specifically stain intracellular lipid droplets with a high signal‐to‐noise ratio, high biocompatibility, and good photostability. Besides, the luminogens exhibit effective reactive oxygen species (ROS) generation capability upon low‐power white light irradiation. Among them, the AIE luminogen, named BDBDC, integrating the NIR emission, good NIR two‐photon absorption and strongest ROS generation demonstrates superior performances in two‐photon fluorescence imaging of various tissues and photodynamic cancer therapy. This molecular design philosophy provides a new way of designing highly bright solid‐state fluorophores for practical applications.