Modular Synthesis of pH-Sensitive Fluorescent Diaza[4]helicenes

摘要: Configurationally stable diaza[4]helicenes have been prepared in two steps by using a particularly facile N–N bond-cleavage reaction. The synthetic procedure uses hydrazine (NH2NH2) for the introduction of single nitrogen atom. strategy is general, modular and highly tolerant to functional groups. A mechanistic rationale proposed spontaneous resulting helical quinacridines are dyes that present absorption emission properties can be modulated as function pH; pink quinacridine green protonated forms (pKa ≈ 9.0) display distinct optical features near-IR region. Single enantiomers were obtained chiral stationary phase HPLC resolution. absolute configurations assigned comparison ECD spectra conjugated acids with those known dialkylquinacridinium derivatives. rather high racemization barrier was measured means variable-temperature experiments (ΔG‡ = 30.7 ± 4.0 kcal mol–1 at 140 °C).