(Invited) Toward Spectral Homogeneity in Guanine Functionalized SWCNTs

Abstract

Different chiralities of single-walled carbon nanotubes (SWCNTs) have distinct electronic and optical properties, with a range of band gaps that make them appropriate for several opto-electronic applications. Due to the unusually high mobility of charge carriers in SWCNTs,1 semiconducting SWCNTs may find use as logic gates in future high-speed nano-electronic circuits. With this in mind, controlled modulation of the optical and electronic properties of individual carbon nanotubes may be valuable in optoelectronic and nano-bioelectronic applications.It was recently discovered that when SWCNTs coated with single-stranded DNA are exposed to singlet oxygen, the guanine nucleobases in the DNA coatings form covalent bonds to the nanotube sidewalls.2 This alters the nanotube electronic and optical properties, allowing spatial and energetic control through selection of the DNA base sequence. However, the functionalized products display undesired spectral broadening interpreted as excess inhomogeneity compared to the pristine SWCNT reactants.Here we will present the results of efforts to understand and reduce this inhomogeneity. Our study has used molecular dynamics simulations of ssDNA – SWCNT hybrid structures, as well as analysis of experimental data. We have explored the effects of varied reaction conditions, including temperature, ionic strength, and pH on product yields and spectra. An unexpected inverse dependence of functionalization density on reaction temperature was uncovered. We will also present photophysical results extracted from spectral data via statistical modeling, including the energy depth of localized exciton quantum wells created by functionalization. The analysis points to fluorescence red shifts that reflect the random number of functionalization sites felt by excitons. Dürkop, T.; Getty, S. A.; Cobas, E.; Fuhrer, M. S. Extraordinary Mobility in Semiconducting Carbon Nanotubes. Nano Lett. 2004, 4, 35-39.Zheng, Y.; Bachilo, S. M.; Weisman, R. B. Controlled Patterning of Carbon Nanotube Energy Levels by Covalent DNA Functionalization. ACS Nano 2019, 13, 8222-8228.