Delayed Fluorescence from Carbon Nanotubes through Singlet Oxygen-Sensitized Triplet Excitons

Abstract

Single-wall carbon nanotubes (SWCNTs) in liquid suspension have been observed to emit delayed, microsecond-scale fluorescence arising from upconverted triplet excitons that are directly created through energy transfer from singlet oxygen molecules (1O2). The singlet oxygen is produced through quenching of an optically excited organic sensitizer. The mechanism of this delayed fluorescence has been deduced from measurements of time-resolved emission kinetics, delayed emission spectra, and polarization-resolved excitation–emission spectra. The observed strong dependence of 1O2 sensitization efficiency on SWCNT structure suggests that (7,6) triplet excitons have an energy near 970 meV. The yields for E 11 T → E 11 S upconversion are found to be in the range of several percent. These yields increase with increasing temperature and decrease with increasing excitation intensities, reflecting thermal activation and triplet–triplet exciton annihilation processes.

Formation of organic color centers in air-suspended carbon nanotubes using vapor-phase reaction

“…The comparable lifetimes also indicate that the vapor-phase reaction can form as high-quality color centers as the solution-processed methods. Although the diameter dependence of the potential depth for E exciton suggests its triplet nature, the observed lifetime is several orders of magnitude shorter than 30–200 μs reported for the triplet states 46 , 52 . Lifetime shortening may be caused by hybridization of the singlet and triplet excitons 53 .…”

Interaction of Luminescent Defects in Carbon Nanotubes with Covalently Attached Stable Organic Radicals

“…As long lifetimes (>1 μs) are a hallmark of triplet states in organic materials, we also looked for delayed fluorescence at room temperature. , To this end, the PL decay of PTM-functionalized SWCNTs was monitored at the E 11 or E 11 * peak emission wavelength by TCSPC over a time window of 0.3 μs. However, in neither case was a component with μs lifetime detectable.…”

Oxime as a general photocage for the design of visible light photo-activatable fluorophores

“…Singlet oxygen exhibits characteristic phosphorescence at 1275 nm. [72][73][74][75] However, none of our oxime-caged uorophores showed detectable phosphorescence emission peaks around 1275 nm, indicating that singlet oxygen does not participate in their photoactivation (Fig. 3B and S18 †).…”