Two-photon excitation (TPE) phototherapy provides high spatial resolution and deep-tissue penetration with minimal invasiveness. In this study, we introduce a modular and scalable approach to transform a traditional TPE imaging dye into a highly effective type-I photosensitizer (PS) through minimal chemical modification. The newly developed selenium-bridged dye demonstrates pronounced two-photon absorption, efficient ROS generation upon TPE, and strong antitumor activity both in vitro and in hypoxic in vivo tumor environments. For subcellular targeting, we conjugated organelle-specific functional groups to produce a series of derivatives, thereby achieving accurate ROS localization and improved PDT efficacy. Leveraging the amphiphilic properties of these PSs, we established a self-assembled dye-combination micelle (DCM) approach that enables the co-assembly of membrane- and mitochondria-targeted derivatives into stable, carrier-free nanoparticles. This multi-dye strategy facilitates enhanced phototoxicity by simultaneously impairing multiple organelle functions. Additional surface modification using the RGD (Arg-Gly-Asp) peptide sequence imparts tumor selectivity through α_vβ₃ integrin-mediated uptake, yielding DCM nanoparticles that selectively induce phototoxic effects in cancer cells while sparing healthy tissue. Importantly, this platform demonstrates spatially restricted, two-photon-triggered therapeutic efficacy in freshly excised human colon tumor tissue, emphasizing its potential for clinical translation.