a tetrapyrollic photosensitizer compound having at least one pendant — ch 2 ch 2 con 2 ) 2 or — n 2 group or esters thereof said tetrapyrollic compound being a chlorin , bacteriochlorin , porphyrin , pyropheophorbide , purpurinimide , or bacteriopurpurinimide . desirably the compound has the formula : or a pharmaceutically acceptable derivative thereof , wherein r 1 - r 8 and r 10 are various substituents and r 9 is substituted or unsubstituted — ch 2 ch 2 con 2 ) 2 ; or — n 2 . the invention also includes a method of treatment by photodynamic therapy by treatment with light after injecting the compound and a method of imaging by fluorescence after injection of the compound .