Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

Effective hydrogen evolution from water using SWCNT photocatalyst under near-infrared (NIR) light illumination was demonstrated. H 2 evolution reactions of 1.2 and 0.40 mmol/h were observed upon chirality-selective photoexcitation by the use of monochromatic light irradiation at 680 and 1000 nm, which are the E 22 and E 11 absorptions of (8,3) SWCNT, respectively, by the use of SWCNT/ fullerodendron photosensitizer in the presence of a sacrifice donor, an electron relay, and a co-catalyst. Apparent quantum yields of this reaction were 0.17 (at 680 nm) and 0.073 (at 1000 nm), respectively. The result provides the first example of photocatalytic H 2 evolution reaction triggered by E 11 photoexcitation of SWCNTs, and clearly shows the usefulness of SWCNTs in the light absorber for NIR light, which is the second main component of solar radiation. F rom the view point of renewal energy resources to win the fight against global warming, there is increasing focus on the production of hydrogen from water using sunlight and photocatalysts because this water splitting reaction does not emit greenhouse gases [1]. For practical use of solar energy, visible-and near-infrared-(NIR) light driven photocatalysts are required to achieve useful and efficient H 2 production because approximately 85% of solar energy incident on the Earth's surface lies in the wavelength region between 400 and 1350 nm [2]. Although many researchers developed visible-light driven photocatalysts for the water splitting, the examples of efficient photocatalysts producing H 2 under NIR light illumination are quite rare [3].Meanwhile, single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n,m) [4]. But their application for solar energy conversion is difficult because of the large binding energy (> 100 meV) of electron-hole pairs, known as excitons, produced by optical absorption [5]. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C 60 is the key for high power conversion efficiency [6]. In contrast to thin film devices, photosensitizing reactions in a dispersion/solution system via photoinduced electron transfer triggered by the photoexcitation of SWCNTs are quite rare because of the difficulty of the construction of a well-ordered surface on SWCNTs. Recently, we developed water-dispersible coaxial nanowires possessing a SWCNT/C 60 heterojunction that can be used for a photosensitizer to produce H 2 from water [7][8][9]. The photosensitizing property of SWCNT was firstly evidenced by chirality-selective photo-excitation by monochromatic light irradiation at 680 nm [9], which is E 22 absorption of (8,3)SWCNT (Figure 1). Apparent quantum yield (AQY) of H 2 evolution reaction using (8,3)SWCNT/ fullerodendron was estimated to be 1.5% at 680 nm. However, it still remains unclear whether E 11 absorption in NIR region is effective for H 2 p...