Long‐lived room temperature phosphorescence from organic molecular crystals attracts great attention. Persistent luminescence depends on the electronic properties of the molecular components, mainly π‐conjugated donor–acceptor (D‐A) chromophores, and their molecular packing. Here, a strategy is developed by designing two isomeric molecular phosphors incorporating and combining a bridge for σ‐conjugation between the D and A units and a structure‐directing unit for H‐bond‐directed supramolecular self‐assembly. Calculations highlight the critical role played by the two degrees of freedom of the σ‐conjugated bridge on the chromophore optical properties. The molecular crystals exhibit RTP quantum yields up to 20 % and lifetimes up to 520 ms. The crystal structures of the efficient phosphorescent materials establish the existence of an unprecedented well‐organization of the emitters into 2D rectangular columnar‐like supramolecular structure stabilized by intermolecular H‐bonding. Rationally designed metal‐free chromophores capable of H‐bonded directed supramolecular self‐assembly and σ‐conjugation allow building molecular crystals exhibiting outstanding long‐lived room temperature phosphorescence. Single crystal analysis reveals a columnar‐like supramolecular structure stabilized by intermolecular H‐bonding. From this, guidelines for obtaining efficient long‐lived phosphorescent molecular crystals are established.