Polymeric　or　organic　semiconductors　are　promising　candidates　for　photocatalysis　but　mostly　only　show　moderate　activity　owing　to　strongly　bound　excitons　and　insufficient　optical　absorption.　Herein,　we　report　a　facile　bottom-up　strategy　to　improve　the　activity　of　a　carbon　nitride　to　a　level　in　which　a　majority　of　photons　are　really　used　to　drive　photoredox　chemistry.　Co-condensation　of　urea　and　oxamide　followed　by　post-calcination　in　molten　salt　is　shown　to　result　in　highly　crystalline　species　with　a　maximum　π–π　layer　stacking　distance　of　heptazine　units　of　0.292　nm,　which　improves　lateral　charge　transport　and　interlayer　exciton　dissociation.　The　addition　of　oxamide　decreases　the　optical　band　gap　from　2.74　to　2.56　eV,　which　enables　efficient　photochemistry　also　with　green　light.　The　apparent　quantum　yield　(AQY)　for　H2　evolution　of　optimal　samples　reaches　57　%　and　10　%　at　420　nm　and　525　nm,　respectively,　which　is　significantly　higher　than　in　most　previous　experiments.　©　2017　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim