Spectroscopic properties of the receptors based on 2- and 3-linked tri(indolyl)methanes for anion binding

The anion binding properties of two title tri(indolyl)methane compounds have been evaluated by using UV–vis absorption and fluorescence spectroscopy. Different from 3-linked receptor which exhibited faint even no obvious spectral response to anions, 2-linked receptor can bind F−, AcO− and H2PO4−, with the bathochromic shifts of the UV absorption and fluorescence quenching. This selectivity will be attributed to suitable steric array of NH binding sites of 2-linked receptor, which helps to form multiple hydrogen bonding interactions with anions.