In principle, a good photocatalyst should be a semiconductor that has a moderate band gap (~1.5 -3.0 eV) to guarantee efficient light absorption in the broad spectrum of solar light while providing photo-excited electrons/holes with sufficient energy to overcome the positive Gibbs free energy change (∆G ≈ 237 kJ mol -1 ) of water redox reaction . These critical requirements have confined possible candidates of commonly known materials and suggest that effective metal-free photocatalysts should be developed on the basis of materials classes with a wide potential of design options, such as 2D conjugated polymers (2DCPs).