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Increasing interest has been noted in photosensitizer design. Currently, most small molecular photosensitizers have several drawbacks, including limited penetration depth and unsatisfying photostability. For addressing these limitations, Frequency upconversion luminescence (FUCL) small molecule was adopted as a photosensitizer design strategy for its deeper penetration, sensitive imaging, and better photostability. We developed a series of FUCL (NIR-NH 2 , NIR-NHEt, NIR-NEt 2) molecules with rigid structures. Equipped with the most powerful electron donor, NIR-NEt 2 exhibits the highest singlet oxygen generation, the strongest upconversion luminescence intensity under 808 nm irradiation and mitochondria-targeted ability. FUCL can be a superior molecular platform for image-guided photodynamic therapy of cancer cells. We developed a series of mitochondria-targeted small FUCL molecules (NIR-NH 2 , NIR-NHEt, and NIR-NEt 2) with different electron-donating segments and screened for the most outstanding one, NIR-NEt 2 , applied for the photodynamic therapy of cancer cells, which demonstrating a new molecular platform for deep-seated upconversion photodynamic therapy. [Display omitted] • FUCL is a one-photon process with advantages of deeper penetration, higher signal-to-noise ratio, and more excellent photostability over the traditional down-conversion luminescence. • NIR-NEt 2 was screened from a series of frequency upconversion luminescence molecules for the excellent photostability, best FUCL ability and ROS generation. • The tactic of heavy-atom free of FUCL PSs that modify strong donating groups on the electron-donating part of D-A structure was investigated. [ABSTRACT FROM AUTHOR]