An Al3+ and H2PO4−/HSO4− selective conformational arrest and bail to a pyrimidine-naphthalene anchored molecular switch

Abstract

A pyrimidine-naphthalene anchored Schiff base (receptor 1) showed Al³⁺ selective conformational arrest by inhibition of its CN isomerization (cis-trans) leading to its fluorescent switching in aqueous medium. Nevertheless the H₂PO₄⁻/HSO₄⁻ bailed receptor 1 from the Al³⁺ arrest leading to its switching ‘off’. This conformational arrest and bail of receptor 1 were highly specific as no other ion pairs were able to do the same. The detection limit of the receptor 1 towards Al³⁺ is 1.49 × 10⁻⁹ M and is the second highest for the same reported to date in the literature, while the same for H₂PO₄⁻ and HSO₄⁻ were found to be 2.27 × 10⁻⁷ and 2.91 × 10⁻⁶, respectively. The mechanistic details of ‘on-off’ switching of the receptor 1 by the analytes have been explored through various spectroscopic studies along with theoretical calculations at density functional theory (DFT) level. The ‘on-off’ switching of receptor 1 through inputs Al³⁺ and H₂PO₄⁻/HSO₄⁻ led it to mimic with INH logic function.