A　series　of　two-dimensional　polyimide　covalent　organic　frameworks　(2D　COF)　based　on　core-substituted　naphthalene　diimides　(cNDIs)　were　designed　and　synthesized　with　the　characteristic　of　tunable　bandgap　without　global　structural　changes.　Cyclic　voltammetry　(CV)　and　DFT　calculations　indicated　that　COFcNDI-OEt　and　COFcNDI-SEt　possess　higher　HOMO/LUMO　levels　and　narrower　bandgaps　than　COFNDI-H.　Further　investigation　indicated　that　the　COF　bandgaps　are　not　only　related　to　the　electron-donating　substituents　but　also　varied　with　respect　to　the　interlayer　distances.　Moreover,　the　femtosecond　transient　absorption　(TA)　spectra　manifested　that　the　electron　donor　substituents　are　beneficial　to　the　charge　delocalization　in　the　π-columnar　unit,　resulting　in　a　longer　lifetime　of　charge　recombination,　which　is　one　of　the　pivotal　prerequisites　for　high-performance　solar　cells　and　photocatalysis.　©　2023　American　Chemical　Society.