Our experiments demonstrated that the electron densities of the aryl rings in catechols positively correlated with the amplitude of their optical response. Electron deficient catechols typically elicit lower optical responses compared to electron rich ones (Fig. , Fig. ). Given the strong correlation between catechol electron densities and their reduction potential, we investigated whether the oxidation of catechols and subsequent electron transfer to nanotubes might underlie the observed optical modulation. However, we found that catechols do not undergo oxidation when exposed to excited ssDNA-SWCNT conjugates, suggesting that a transient perturbative process, rather than permanent charge transfer, is more likely for the optical modulation. Through a systematic exploration of the derivatized catechols and related compounds, we identified aminocatechols and phenylenediamines as substrates that can elicit robust optical responses from ssDNA-SWCNT conjugates, thereby expanding the substrate scope detectable by (GT)N-SWCNT bio-nano conjugates. Moreover, we observed that the optical response of certain analytes was highly sensitive to solution pH, indicating that the protonation state (charge) of the various substituents on the aryl group play a key role in the molecular recognition and optical modulation process.