Covalent　organic　frameworks　(COFs)　constitute　a　promising　research　topic　for　photocatalytic　reactions,　but　the　rules　and　conformational　relationships　of　1D　COFs　are　poorly　defined.　Herein,　the　chain　edge　structure　is　designed　by　precise　modulation　at　the　atomic　level,　and　the　1D　COFs　bonded　by　C,　O,　and　S　elements　is　directionally　prepared　for　oxygen-tolerant　photoinduced　electron　transfer-atom　transfer　radical　polymerization　(PET-ATRP)　reactions.　It　is　demonstrated　that　heteroatom-type　chain　edge　structures　(─O─,　─S─)　lead　to　a　decrease　in　intra-plane　conjugation,　which　restricts　the　effective　transport　of　photogenerated　electrons　along　the　direction　of　the　1D　strip.　In　contrast,　the　all-carbon　type　chain　edge　structure　(─C─)　with　higher　intra-plane　conjugation　not　only　reduces　the　energy　loss　of　photoexcited　electrons　but　also　enhances　the　carrier　density,　which　exhibits　the　optimal　photopolymerization　performance.　This　work　offers　valuable　guidance　in　the　exploitation　of　1D　COFs　for　high　photocatalytic　performance.　This　work　offers　valuable　guidance　in　the　exploitation　of　1D　COFs　for　high　photocatalytic　performance.　©　2024　Wiley-VCH　GmbH.