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

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. A strategy for designing aggregation-induced emission (AIE) materials and enhancing the solid-state fluorescence based on tuning molecular packing by twisting molecular structure is proposed. Based on this strategy, a series of AIE fluorophores exhibiting highly efficient solid-state fluorescence, wide emission color tunability, and good two-photon absorption are facilely developed for two-photon imaging of lipid droplets and photodynamic therapy. image