Solvatochromism in SWCNTs suspended by conjugated polymers in organic solvents

Abstract

Despite the extensive utilization of carbon nanostructures as sensors, the factors that most affect their performance remain insufficiently understood. Many nanocarbon-based sensors are either processed in liquid environments or applied as liquid suspensions, which leads to solvatochromism, substantially influencing the underlying optical transitions. Most of the principles established so far apply only to nanocarbon species dispersed in polar environments by common surfactants, so the reported findings are not universal. For instance, they cannot describe the behavior of single-walled carbon nanotubes (SWCNTs) suspended in organic solvents by conjugated polymers (CPs), which have recently received considerable attention from the scientific community. Our research responds to this lack of knowledge and provides a thorough understanding of this topic by investigating SWCNT nanocomposites based on polyfluorenes and their co-polymers. A careful selection of an autonomous reference and precise spectral analysis allowed us to measure absolute solvatochromic shifts, by using which we identified and derived the underlying relationships affecting the optical properties of the material. Elucidation of the complex interactions between the polymer structure, SWCNT chirality, and solvent characteristics gave rise to the formulation of a revised mechanism of solvatochromism in SWCNTs. The in-depth experimental and theoretical examination revealed that in the case of CP-solubilized SWCNTs, the solvatochromic shifts strictly depend on the assignment of individual chiral types to mods and families, which experience the strain exerted by the polymer chains in different ways.