Graphitic carbon nitride (g-C3N4) is among the most promising metal-free photocatalysts for H-2 production from solar-driven water reduction. However, the photocatalytic efficiency of bulk g-C3N4 powders is limited. In this work, molecular aggregates of perylene tetracarboxylic diimides (PTCDIs, a robust class of air-stable n-type organic semiconductor) were loaded via solution processing on the surface of g-C3N4, which is pre-deposited with cocatalyst Pt nanoparticles. The PTCDIs/Pt/g-C3N4 composites thus fabricated exhibit broader visible-light response than Pt/g-C3N4, and possess excellent photochemical stability. The initial intramolecular charge transfer features of the PTCDIs, as well as their energy levels being matched to g-C3N4, ensure subsequent charge separation in the PTCDIs/Pt/g-C3N4 composites. When the composites are dispersed into aqueous solutions containing triethanolamine as a sacrificial electron donor, a tenfold enhancement of H-2 evolution activity (similar to 0.375 mu mol h(-1)) is achieved compared to bare Pt/g-C3N4 under visible-light (lambda >= 420 nm) irradiation. (C) 2015 Elsevier B.V. All rights reserved.