Ring-opening disulfide exchange polymerization has recently been identified as ideal for synthesizing single-channel photosystems by self-organizing surface-initiated polymerization (SOSIP). Here we introduce chemoorthogonal hydrazone exchange chemistry to engineer additional channels into single-channel photosystems. Post-SOSIP stack exchange is shown to provide facile access to complete supramolecular n/p-heterojunction architectures with high activity and freely variable composition, including oriented antiparallel redox gradients. With appropriate templation from the surface, post-SOSIP stack exchange is nearly quantitative.