Continuous irradiation during photodynamic therapy (PDT) process inevitably induces tumor hypoxia, thereby weakening the PDT effect. In the PDT induced temporary hypoxia, sustainably providing singlet oxygen from stored chemical energy may enhance the cell killing effect and boost the phototheranostics. Herein, we present a phototheranostics (DPPTPE@PEG-Py NPs) by using 2-pyridone based diblock polymer (PEG-Py) to encapsulate a semiconducting heavy atom free pyrrolopyrrolidone-tetraphenylethylene (DPPTPE) with high singlet oxygen generation ability both in dichloromethane and water. In the phototheranostics, the designed PEG-Py can trap the 1O2 generated from DPPTPE under laser irradiation and form a stable intermediate of endoperoxide, which can then chemically release 1O2 in both dark and hypoxic tumor microenvironment. In comparison with DSPE-PEG encapsulated DPPTPE (DPPTPE@DSPE-PEG), much lower half maximum inhibitory concentration (IC50) was observed in four types of cancer cell lines, including HeLa, HCT-116, A549 and MCF-7 under laser irradiation after being uptaken by DPPTPE@PEG-Py NPs. Furthermore, the fluorescence imaging guided phototherapy study demonstrates that our designed phototheranostics could completely inhibit the tumor growth with the help of laser. This study provides a paradigm to develop highly efficient photosensitizers with photodynamic and photothermal capability for personalized cancer therapy.