Organic dyes with multi-branched structures for highly efficient photocatalytic hydrogen evolution under visible-light irradiation

Direct photocatalytic water splitting is an attractive strategy for clean energy, in which, organic photocatalytic systems with broad light-harvesting region and efficient charge separation are highly desired and still challenging. In this paper, three multi-branched organic dyes were designed and synthesized with dipolar, V-shaped, and octupolar geometries, respectively. The multiple intramolecular charge transfer processes by electronic pull-push effect along the branches can provide more channels for light-harvesting and carrier transporting. Also, the interactions with polymeric carbon nitride (PCN) can be optimized by multiple anchoring units and defect filling effect, resulting in the gradually enhanced photocatalytic hydrogen evolution performance with the increased number of branches. Accordingly, the highest one of 996.9 μmol h −1 was achieved, which is over 40-folders that of PCN/Pt (24.8 μmol h −1 ) under the same conditions. It provides an efficient strategy for molecular design of organic dyes as photocatalyst, promoting development of PHE system from the molecular level. Organic dyes with different branched structures, as dipolar, V-shaped and octupolar configurations, were applied to PCN surface as photocatalyst, with the aim to promote photocatalytic hydrogen evolution (PHE). Accordingly, PHE rates enhanced with increased number of branches, and the highest one of 996.9 μmol h −1 was achieved by octupolar dye, which was over 40-folders that of PCN/Pt (24.8 μmol h −1 ). It indicated the superiority of branched structure, which is mainly related to the stronger light-harvesting ability and optimized interactions between dye and PCN with multiple anchoring units. • Organic dyes with multi-branched structure can promote photocatalytic hydrogen evolution by optimized interactions. • The highest PHE rate reach to 996.9 μmol h −1 , and AQY efficiency of 12.5% at 490 nm. • The charge transfer processes were investigated systematically by varied emission properties under different conditions.