Efficient Quenching of Singlet Oxygen via Energy Transfer to Semiconducting Single-Walled Carbon Nanotubes

Abstract

Singlet oxygen, 1O2(a1Δg), is efficiently deactivated by single-walled carbon nanotubes (SWNTs) having diameters in the range d ≈ 1−1.6 nm. This is evidenced by quenching of the near-infrared emission of photosensitized 1O2 in water−surfactant dispersions of SWNTs. The observed quenching rate is close to the diffusion-limited value. The smaller diameter SWNTs are found to be comparatively less active, despite the presence of metallic tube types. We therefore attribute the quenching to energy transfer from 1O2 to primarily semiconducting SWNTs having a sufficiently small band gap (d ≥ 1 nm). Remarkably, photogeneration and quenching of up to ∼109 singlet oxygen molecules per nanotube (ultimately limited by degradation of the rose bengal sensitizer) does not affect the photoluminescence and absorption spectra of SWNTs. This indicates that dispersed SWNTs are highly chemically inert toward 1O2 and provides additional support for the proposed physical (energy transfer) quenching mechanism.