P hotoacoustic (PA ) imaging is a n emerging non - invasive biomedical imaging modality to obtain deep tissue images in optical sensitivity and ultrasound resolution. Currently several clinical applications are being explored , e.g. sentinel lymph node detection , imaging of tissue oxygenation , Crohn ’ s disease , and cancer detection , which may significantly improve diagnostic imaging sensitivity in future . To gain high contrast in vivo applications , exogenous contrast agents showing absorption in the near infrared range (NIR , > 700 nm) are applied. Hence we are pursu ing the development of novel contrast agents suitable for PA imaging . N on - fluorescent organic ch ro mophor es are better sui ted for PA imaging since they exhibit fa vourable pharmacokinetic proper t i es as well convert efficiently the absorbed energy into thermoelastic expansion that eventually give the PA signal. Therefore, the synthesi s of novel near infrared absorbing quenche r chromophore s has been ongoing in our group . We prepared quinone fused porphyrin s and explored their PA properties to obtain PA signal maxima at 732 nm with detection sensitivity below one nano mol e . Further, we developed superoxide ion responsive oxo porphyr i n ogen probe t h at show ed increase in PA signal amplitude wit h simultaneous red shift in PA maximum after ROS activation. BODIPY dyes are another interesting class exhibit ing NIR - absorption band s but strongly fluoresce . Hence , we designed and synthe sized quencher BODIPYs (PyBDPs) by applying photo induced electron transfer principles. We achieved unprecedented red shift in absorption ( to 800 nm ) by pyrrole conjugation s , which gave PA signal at concentrations as low as 1 00 pmol . Th e s e PyBD P dye s exhibit no phototoxicity, are high ly biocompatib l e ( non - toxic up to 100 μM , in XTT assays ) , and stab l e in fetal calf serum (FCS) media for over 24 hours . T ether ing PyB DP dye s to various receptor - targeting moieties for selectiv e binding to pathogenic tissues , nanoparticle formulations for by passive uptake to tumor imaging are currently ongoing , and preliminary results will be discussed