Synthesis of indenophenanthridine via a [4+2] annulation strategy: a “turn-off’’ Fe3+ ion sensor, practical application in live cell imaging and reversible acidochromism studies

Abstract

An efficient protocol has been developed for the synthesis of a novel fluorescent probe, 1,2-disubstituted-indeno[1,2,3-gh]phenanthridine, derived from a series of α-oxo-ketene dithioacetals (OKDTAs) and indenoquinoline under essential conditions via a [4+2] annulation in excellent yield. All the synthesized indenophenathridine derivatives were well characterized by NMR and mass spectrometry. One of the synthesized indenophenanthridine derivatives, 4b, has been involved in acidochromism studies, selectively sensing Fe³⁺ ions in non-aqueous solution with a low detection limit (7.5 × 10⁻⁷ M) applied in live-cell bio-imaging.