the observed absorbance red shift can also be due to aggregation in 1,4-dioxane solution (vide supra). Overall, the nucleobase identity tunes the absorption maxima up to 20 nm within each series, best read out from the DMF absorption data. Furthermore, the molar extinction coefficient observed for the low-energy absorption of 1a−d is reduced by at least a factor of 2 compared to that of the absorption of 2ad