A　series　of　new　silicon(IV)　phthalocyanines　(SiPcs)　di-substituted　axially　with　different　nucleoside　moieties　have　been　synthesized　and　evaluated　for　their　singlet　oxygen　quantum　yields　(Phi(Delta))　and　in　vitro　photodynamic　activities.　The　adenosine-substituted　SiPc　shows　a　lower　photosensitizing　efficiency　(Phi(Delta)　=　0.35)　than　the　uridine-　and　cytidine-substituted　analogs　(Phi(Delta)　=　0.42-0.44),　while　the　guanosine-substituted　SiPc　exhibits　a　weakest　singlet　oxygen　generation　efficiency　with　a　Phi(Delta)　value　down　to　0.03.　On　the　other　hand,　replacing　axial　adenosines　with　chloro-modified　adenosines　and　purines　can　result　in　the　increase　of　photogenerating　singlet　oxygen　efficiencies　of　SiPcs.　The　formed　SiPcs　1　and　2,　which　contain　monochloro-modified　adenosines　and　dichloro-modified　purines　respectively,　appear　as　efficient　photosensitizers　with　Phi(Delta)　of　0.42-0.44.　Both　compounds　I　and　2　present　high　photocytotoxicities　against　HepG2　and　BGC823　cancer　cells　with　IC50　values　ranging　from　9　nM　to　33　nM.　The　photocytotoxicities　of　these　two　compounds　are　remarkably　higher　than　the　well-known　anticancer　photo　sensitizer,　chlorin　e6　(IC50　=　752　nM　against　HepG2　cells)　in　the　same　condition.　As　revealed　by　confocal　microscopy,　for　both　cell　lines,　compound　I　can　essentially　bind　to　mitochondria,　while　compound　2　is　just　partially　localized　in　mitochondria.　In　addition,　the　two　compounds　induce　cell　death　of　HepG2　cells　likely　through　apoptosis.　(C)　2016　Elsevier　B.V.　All　rights　reserved.