Photocatalysis using polymeric carbon nitride (CN) materials is a constantly evolving field, where the variation of synthetic procedures allows the constant improvement of activity by tackling the intrinsic limitations of these materials (optical absorbance, specific surface area, charge migration, etc.). Amongst the possible photocatalytic reactions, the most popular application of CNs is the hydrogen evolution reaction (HER) from water. In this work, we design precisely-controlled carbon-doped porous CN rods with extended π-electron conjugation from supramolecular assemblies of melem and co-monomers, which partially substitute nitrogen for carbon atoms at the pyrimidine ring of the melem. Dense hydrogen bonds and good thermal stability of the melem-based supramolecular framework allow synthesizing a more ordered structure for improved charge migration; the control from the molecular level over the position of carbon-substituted nitrogen positions tailors the band alignment and photogenerated charge separation. The optimal photocatalyst shows an excellent HER rate (up to 10.16 mmol·h⁻¹·g⁻¹ under 100 W white light-emitting diode (LED) irradiation, with an apparent quantum efficiency of 20.0% at 405 nm, which is 23.2 times higher compared to a reference bulk CN). To fully harness the benefits of the developed metal-free CNs, selective oxidation reaction of aromatic alcohols is demonstrated with high conversion and selectivity.