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.