(Invited) Stochasticity in the Number of Quantum Defects in Fluorescent Carbon Nanotubes

Abstract

Single wall carbon nanotubes (SWCNTs) display chirality dependent near infrared (NIR) fluorescence. Their optoelectronic properties can be further tuned by incorporating quantum defects/organic color centers (OCC) via reactions with diazonium salts. The absolute number of defects per SWCNT determines the properties but is not exactly known. Measuring it is complicated because typical SWCNT samples contain multiple chiralities, that congest the spectra and prevents to distinguish defects from different chiralities. Aqueous two-phase extraction (APTE) is a powerful technique to isolate specific chiralities. Here, we show that quantum defects do not affect APTE, which indicates that the chemical potential is not substantially affected and pinpoints to low numbers of defects. The purity of (6,5)-SWCNTs allows us to image the NIR fluorescence contributions (E11 below 1050 nm, and E11 * above 1050 nm) on the single SWCNT level and defect incorporation itself on the single molecule level. Interestingly, one observes a stochastic distribution of the numbers of defects, which can be explained by a Poisson distribution. We find a mean number of defects of 0-3 per SWCNT. These results indicate the large variance between ensemble and single particle picture. In summary, we show that single quantum defects can be counted by NIR imaging and that stochasticity plays a crucial role for their optical properties.