Morphology and Optical Response of Carbon Nanotubes Functionalized by Conjugated Polymers

Noncovalent functionalization of single wall carbon nanotubes (SWNTs) by biological and conjugated polymers promises significant improvements in their properties important for future nanotube-based optoelectronic and photovoltaic devices. Using a combination of molecular mechanics and quantum chemistry methods, we investigate how the deposition of poly-phenylene vinylene (PPV), a conjugated polymer, on the surface of selected SWNTs affects their morphology, as well as their electronic and optical properties. We found that the interaction between PPV and the nanotube is relatively weak (0.1–0.3 eV per repeat unit), and the most stable structures exhibit small coiling angles (≤20°) of PPV chains around the nanotube. PPV functionalization weakly affects optical excitations of the SWNT, resulting in slight red-shifts of the first and second optical bands of the nanotube. In contrast, the absorption spectra of PPV are strongly affected by specific conformational structures of the wrapped polymer. Our analysis identifies and explains a significant blue-shift of the excited energy and much broader line-width of the coiled PPV compared to that of the respective isolated polymer structures. These trends convey that signatures of polymer wrapping around SWNTs can be detected in experimental optical spectra of hybrid composites