报告人: R. Bruce Weisman
Department of Chemistry, Rice University, Houston, Texas  USA

Single-walled carbon nanotubes (SWCNTs) are tubular structures of sp²-bonded carbon atoms with high aspect ratios and long-range crystalline order. Each SWCNT structure has a delocalized pi-electron system whose energy levels reflect quantum confinement. It has been found that SWCNTs undergo several types of interesting interactions with oxygen. When exposed to O₃, SWCNTs readily form a 1,2-ozonide adduct that photochemically converts into an oxide by losing O₂. The most stable oxide product is an ether structure in which all carbon atoms remain sp²-hybridized. These O-doped nanotubes have nearly pristine absorption spectra but show intense red-shifted optical emission at short-wave infrared wavelengths. The new emission is assigned to mobile excitons that become trapped at the lower energy doping sites. In a completely different type of interaction, surfactant-coated SWCNTs in water suspension can show partial fluorescence quenching by dissolved O₂. The amount of this quenching varies strongly with surfactant coating, reflecting how completely the SWCNT surface is protected. When the coating is single-stranded DNA oligos, the fluorescence quenching reveals selective affinities between specific ssDNA sequences and specific SWCNT structures. A third type of oxygen interaction occurs between dissolved O₂ and SWCNTs that are strongly irradiated at their short-wave infrared absorption peaks. The result is persistent and spectrally localized fluorescence quenching resulting from a selective photochemical reaction. This process allows the optical properties of mixed SWCNT samples to be tailored by targeted photochemistry. Finally, I will present recent evidence that SWCNT triplet excited states can be formed through solution-phase energy transfer from O₂ in its excited singlet state. The key observation is weak delayed SWCNT fluorescence, which is thought to come from thermal excitation of long-lived SWCNT triplet excitons to emissive singlet exciton states.