Dye/polymeric　carbon　nitride　(PCN)　systems　exhibit　great　potential　for　photocatalytic　hydrogen　evolution　(PHE),　due　to　the　broad　light-harvesting　region　and　optimized　charge　separation　ability.　However,　charge　recombination　due　to　the　unmatched　photogenerated　carrier　lifetimes　(ns　level)　of　organic　dyes　and　photocatalytic　reaction　rates　(s　level)　is　a　major　hindrance,　which　afforded　a　big　challenge　to　modulate　electronic　processes　by　prolongation　of　carrier　lifetimes　of　dyes.　Herein,　the　excited　triplet　states　of　organic　dyes　with　longer　carrier　lifetimes　(ms　level)　were　employed　in　PHE　systems　for　the　first　time,　which　are　stabilized　by　the　adjustment　of　π-π　interactions　of　conjugation　skeletons　with　alkyl　chain　engineering.　By　utilizing　the　increased　isolation　effect　of　alkyl　chains,　from　linear　to　branched　ones　with　prolonged　lengths,　higher　PHE　activities　were　achieved　by　branched　chain-substituted　dyes　due　to　their　longer　lifetimes,　accompanied　by　the　improved　phosphorescence　properties,　and　suppressed　charge　recombination.　Accordingly,　a　relationship　among　properties　of　triplet　excited　states,　alkyl　chains,　and　PHE　activity　has　been　roughly　built,　providing　valuable　information　for　further　promoting　PHE　activities　by　adjustment　of　dye-dye　and　dye-PCN　interactions.　©　2023　The　Royal　Society　of　Chemistry.