Dye-sensitized H₂ evolution from water facilitated by photoinduced electron transfer between molecules on the inside and the outside of a carbon nanotube

Dye-encapsulated single-walled carbon nanotubes (dye@SWCNTs) were physically modified to fabricate a water-dispersible dye@SWCNT/dendrimer hybrid. A photocatalytic H₂ evolution reaction that uses this dye@SWCNT hybrid as a particulate photocatalyst was conducted in the presence of an electron-relay molecule [methyl viologen (MV²⁺)], a co-catalyst [PVP–Pt; poly(vinylpyrrolidone)], and a sacrificial donor [1-benzyl-1,4-dihydronicotinamide]. Photoinduced electron transfer occurs between the encapsulated dye molecule inside the SWCNT and the MV²⁺ ion outside the SWCNT. This is followed by the relay of the electron to the co-catalyst, which reduces H⁺ to generate H₂. The external quantum yield of the H₂ evolution reached a maximum of 8.5% under irradiation with light at 510 nm. Notably, the photoinduced electron transfer between the molecules on the inside and the outside of the SWCNT proceeded smoothly despite the possibility of energy migration from the encapsulated dye to the SWCNT or the possibility of charge recombination.