Computational investigations into new fluorescence quenching process induced by complexation of alkali metal ion

A novel fluorescent switchable chemosensor 1 , which is composed of an anthracene‐modified calix[4]crown in the 1,3‐alternate conformation, was calculated by density functional theory and time‐dependent density functional theory method. Geometries, molecular orbitals and binding thermal energies were evaluated at the restricted hybrid Becke's three‐parameter exchange functional using 6‐31 G(d) basis set and relativistic effective core potentials. The metal–ligand and cation–π interactions were investigated acting as two main types of driving force. Our calculations clearly show that solvent effects strongly influence cation selectivity, and K + selectivity is recovered when even a few waters of hydration are considered. The calculations indicate that because of the photoinduced electron transfer effect, the addition of alkali metal ions have hardly any effect on the fluorescence of ligand 1 under neutral or basic conditions. Also, the high selectivity of ligand 1 for K + and Rb + , under acidic conditions, the complexed metal ion can result in ammonium ion deprotonation, which leads to quenching of fluorescence of 1 •H + . Copyright © 2012 John Wiley & Sons, Ltd.