Mitochondria‐Targeting Phototheranostics by Aggregation‐Induced NIR‐II Emission Luminogens: Modulating Intramolecular Motion by Electron Acceptor Engineering for Multi‐Modal Synergistic Therapy

Abstract Phototheranostic agents have thrived as promising tools for cancer theranostics because of the integration of sensitive in situ fluorescence imaging and effective multi‐model synergistic therapy. However, how to manipulate the intangible photon energy transfer to balance the competitive radiative and nonradiative processes is still challenging. Although numerous phototheranostic molecules are reported, their complicated molecular design and tedious synthesis often stumble further their development. Herein, three simple molecules with electron donating−accepting structures are developed. The electron acceptor engineering on molecules by introducing acridinium unit gives rise to TPEDCAc with aggregation‐induced second near‐infrared emission (AIE NIR‐II), high reactive oxygen species generation capability, and excellent photothermal conversion efficiency (44.8%) due to the drastic intramolecular motion of large acridinium rotor and balanced AIE effect. Experimental analysis and calculation on the controlled molecules suggested that large torsional angle and the strong electron‐withdrawing ability of the acridinium unit are keys for NIR‐II emission and balanced photodynamic/photothermal conversion. Impressively, the positively charged TPEDCAc shows mitochondria‐targeting capability and high performance in in vivo multi‐modal cancer theranostics under NIR laser irradiation. Hence, this work not only provides a single NIR‐II AIE‐based multi‐modal cancer theranostic system but inspires new insights into future development of new theranostic platforms.