Molecular　photoacoustic　imaging　(PA)　is　a　promising　technology　to　understand　tumor　pathology　and　guide　precision　therapeutics.　Despite　the　capability　of　activatable　PA　probes　to　image　tumor-specific　biomarkers,　limitations　in　their　molecular　structure　hamper　them　from　effective　drug　delivery　and　the　drug　release　monitoring.　Herein,　we　developed　a　perylene　diimide　(PDI)　based　theranostic　platform　that　provides　noninvasive　PA　imaging　signals　to　monitor　tumor-specific　pH-responsive　drug　release.　Methods:　we　first　designed　and　synthesized　an　acid-responsive　amine-substituted　PDI　derivative.　The　pH　sensitive　properties　of　the　PDI　was　demonstrated　by　density　functional　theory　(DFT)　calculations,　UV-vis　experiments　and　PA　studies.　The　theranostic　platform　(THPDINs)　was　fabricated　by　self-assembly　of　the　acid-responsive　PDI,　a　pH　irrelevant　IR825　dye,　and　anti-cancer　drug　doxorubicin　(DOX).　The　PA　properties　in　various　pH　environment,　drug　delivery,　cytotoxicity,　cell　uptake,　ratiometric　PA　imaging　and　anti-tumor　efficacy　of　the　THPDINs　were　investigated　in　vitro　and　in　vivo　by　using　U87MG　glioma　cell　line　and　U87MG　tumor　model.　Results:　We　found　that　our　designed　PDI　was　sensitive　to　the　tumor　specific　pH　environment,　reflected　by　absorbance　shift,　PA　intensity　and　aggregation　morphology　changes　in　aqueous　solution.　The　as-synthesized　pH　sensitive　PDI　acted　as　a　molecular　switch　in　the　THPDINs,　in　which　the　switch　can　be　triggered　in　the　mild　acidic　tumor　microenvironment　to　accelerate　DOX　release.　Meanwhile,　the　DOX　release　could　be　monitored　by　ratiometric　PA　imaging.　Conclusions:　We　developed　a　multifunctional　PDI　based　theranostic　platform　for　noninvasive　real-time　ratiometric　PA　imaging　of　tumor　acidic　pH　and　monitoring　of　drug　release　in　living　mice　simultaneously.　This　strategy　will　shed　light　on　the　development　of　smart　activatable　theranostic　nanoplatforms　and　will　significantly　advance　the　application　of　PA　theranostics　in　biology　and　medicine.　©　Ivyspring　International　Publisher.