Antimicrobial　photodynamic　therapy　(aPDT)　is　an　effective　mean　for　killing　bacteria　in　this　era　of　increasing　multi-antibiotic　resistance,　and　possesses　a　number　of　unique　advantages.　Much　effort　has　been　devoted　to　the　development　a　key　component　of　aPDT　photosensitizers　(PSs).　We　synthesized　a　series　of　PSs　with　different　positive　charges　(ZnPc(Lys)(n),　where　n　=　3,　5,　7,　and　studied　their　antibacterial　activities　and　mechanisms　against　Escherichia　coli　(E.　coli).　Interestingly,　the　ZnPc(Lys)(5)　derivative　showed　stronger　antibacterial　effect　(MIC　=　25.3　mu　M)　than　the　other　two　PSs　(MICs　=　50.6　mM),　even　though　this　PS　did　not　have　the　highest　uptake　on　bacteria　among　these　PSs.　It　was　ZnPc(Lys)(7)　that　possessed　the　highest　bacterial　uptake.　ZnPc(Lys)(5)　was　found　to　have　the　highest　monomeric　fractions　(62.0%)　on　bacteria　surface　than　the　other　two　PSs　(37.9%　for　n　=　3　and　33.9%　n　=　7).　These　results　clearly　demonstrate　that　PS　conformation　on　bacterial　surface　as　a　key　parameter　determining　antibacterial　efficacy　of　PSs.　Other　mechanistic　aspects　of　photodynamic　effects,　including　PS　binding　kinetics,　bacterial　surface　hydrophobicity,　zeta　potential　of　bacteria,　membrane　permeability　and　bacterial　signaling　pathways　were　also　studied.