A　series　of　novel　unsymmetrical　silicon　(IV)　phthalocyanines　(SiPcs)　di-substituted　axially　with　tyramine　and　different　oligomeric　ethylene　glycol　moieties　have　been　synthesized　by　alkoxy　exchange　reactions,　and　their　singlet　oxygen　quantum　yields　(ΦΔ)　and　in　vitro　photodynamic　activities　have　also　been　evaluated.　The　unsymmetrical　SiPcs　2–5　show　slightly　higher　photosensitizing　efficiency　(ΦΔ　=　0.08–0.12)　than　the　corresponding　symmetrical　SiPc　1　(ΦΔ　=　0.05),　but　are　less　efficient　compared　to　the　symmetrical　SiPc　6　(ΦΔ　=　0.33).　All　the　compounds　exhibit　high　photocytotoxicities　against　BGC-823　cancer　cells　with　IC50　values　ranging　from　3　nM　to　20　nM.　Particularly　for　the　unsymmetrical　SiPc　5,　the　IC50　value　toward　BGC-823　cells　is　significantly　lower　than　its　corresponding　symmetrical　SiPcs　1　and　6,　which　could　be　attributed　to　its　higher　cellular　uptake.　In　addition,　SiPc　5　can　essentially　bind　to　mitochondria　and　induces　cell　death　of　BGC-823　cells　mainly　through　apoptosis.　So　SiPc　5　is　a　highly　promising　photosensitizer　for　photodynamic　therapy.　©　2020　Elsevier　Ltd