Dynamic and Steady State Optical Studies of Individual Covalent Dopant Sites in Single-Wall Carbon Nanotubes

Controlled low-level covalent functionalization of single-wall carbon nanotubes (SWCNTs) has refocused the attention of the nanophotonics community on the use of SWCNTs as stable photon sources in imaging applications. Recently, a significant increase in photoluminescence (PL) quantum yield from the appearance of new emitting states was reported in the literature upon introduction of chemically stable oxygen [1,2] and aryl diazonium dopants [3]. Further insight into the chemical and electronic structure of oxygen trap sites was gained through low-temperature studies [4],however additional fundamental knowledge about the optical and chemical properties of these dopant sites is necessary in order to develop more efficient emitter and light harvesting systems based on SWCNTs.

We doped single-chirality-enriched (6,5) and (5,4) SWCNTs with a broad range of available covalent dopants and studied their steady-state and dynamic optical properties on the ensemble and single-tube level. Our refinement of the reported doping procedure described in the literature [1-3] enables the control of the doping level and type of dopant down to the introduction of individual dopant sites in a short timescale. Dual color imaging of 2 – 6 μm long SWCNTs reveals the red-shifted individual dopant emission E₁₁* alongside the pristine E₁₁ emission. Average ON times of single sites decrease with increasing electron withdrawing nature of the specific dopant groups as well as with an increase in pH of the surrounding medium which can be understood in terms of additional non radiative decay channels introduced through surface charging. In addition, we will present single tube lifetime measurements on covalently doped (5,4) SWCNTs for a variety of diazonium dopants. The brightening in dopant emission intensity is correlated with longer PL lifetimes and increases with the electron withdrawing strength of the associated functional groups.

[1]  S. Ghosh, et al., Science, 2010, 330, 1656.

[2]  Y. Miyauchi, et al., Nature Photon., 2013, 7, 715.

[3]  Y. Piao, et al., Nature Chem., 2013, 5, 840.

[4]  X. Ma, et al., ACS Nano, 2014, 8, 10782.