The COFLeaf project aims at the development of single-site heterogenous photocatalytic systems which enable the stable photogeneration of solar fuels from abundant precursors – water and CO₂ – through integrating different subsystems necessary for the overall photocatalytic process in one polymeric platform, the “COF leaf”. Special emphasis is placed on the model character of the devised systems which are tailored and modified by molecular synthetic protocols, and optimized by solid-state chemical procedures and crystal engineering so as to provide insights into the architectures, reactive intermediates and mechanistic steps involved in the photocatalytic process. The COFLeaf project thus aims at the development of a modularized photocatalytic platform enabling the adaptation and optimization of each single step involved in solar fuel conversion, and hence presents the holistic development of functional water splitting and carbon dioxide reduction catalysts.