A novel colorimetric and fluorescent sensor for fluoride and pyrophosphate based on fluorenone signaling units

Abstract

In this study, a novel chromogenic receptor, 1-(naphthalen-1-yl)-3-(9-oxo-9H-fluoren-1-yl)urea (1), utilizing fluorenone and naphthalene moieties as signaling groups was designed and synthesized. The interaction and colorimetric sensing properties of receptor 1 with different anions were investigated by the naked eye, as well as UV-visible and fluorescence spectroscopy. The addition of 100 equiv. of fluoride and pyrophosphate as tetrabutylammonium salts to 1.25 x 10(-4) M CH3CN:DMSO (9:1, v/v) solution mixture of receptor 1 produced a wine-red color. The oxoanions and a variety of other anions were not capable of producing any significant color change with receptor 1 under similar experimental conditions. The corresponding UV-vis measurements showed a bathochromic shift of the 395 nm band of receptor 1 to similar to 500 nm for fluoride and pyrophosphate. Fluorescence emission changes indicate clearly that receptor 1 behaves like an ideal photo-induced electron transfer (PET) sensor upon complexation with anions. The limit of detection (LOD) of the sensor 1 is calculated to be ca. 250 and 110 nM for F- and HP2O73-, respectively. The H-1 NMR titration studies shed further light on their mode of binding with receptor 1. The quantum mechanical calculations through time dependant density functional theory (TD-DFT) using basis set B3P86/TZVP support our experimental findings with a good agreement. (c) 2012 Elsevier B.V. All rights reserved.