Anion-induced optical outputs of an isatin-based colorimetric HNI sensor for construction of sequential molecular logic gates and a set-reset memorized device

Anion binding properties of the isatin-based colorimetric HNI sensor ((Z)-3-(hydroxyimino)-5-nitroindolin-2-one) were investigated by UV-vis spectroscopy. Absorption response profiles of HNI varied dramatically for different anionic inputs by controlling the intramolecular charge transfer (ICT). These observations were utilized to construct logic functions of OR, NOR and the complementary INH/IMP sequential circuit. Further, reversible optical switches induced by alternative addition of F− and HSO4− were demonstrated with a 'Write-Read-Erase-Read' memory function possessing 'multi-write' ability.