Colorimetric and fluorimetric detection of Fe(III) using a novel chromenylium-cyanine near-infrared fluorescence probe: Photophysical properties, DFT studies and cell imaging.

A novel chromenylium-cyanine near-infrared fluorescent probe named FTP is devised and successfully fabricated by using a Rhodamine derivative as the fluorescence-generating precursor for selectively and sensitively detecting Fe3+ in aqueous environments. Notably, its maximum emission wavelength reaches up to 743 nm, which lies in the first near-infrared window. The structure of FTP underwent characterization via Fourier Transform Infrared Spectroscopy (FTIR), Liquid Chromatography-Mass Spectrometry (LC-MS) and Nuclear Magnetic Resonance (NMR). The probe FTP demonstrates excellent selectivity and sensitivity toward Fe3+, achieving low detection limits of 79.7 nM (Ultraviolet-visible detection) and 24.0 nM (Fluorescence detection), as well as distinct colorimetric changes and an "off-on" fluorescence response. The 1:1 coordination mechanism between FTP and Fe3+ was further validated through LC-MS, 1H NMR, calculations based on Density Functional Theory (DFT), and an analysis of Job's plot. Notably, FTP exhibits excellent biocompatibility and was successfully applied to fluorescence imaging in MCF-7 and HepG2 cells as well as in living mice, highlighting its potential for disease diagnosis and therapeutic monitoring.