Far‐Red‐Emitting TEG‐Substituted Squaraine Dye: Synthesis, Optical Properties, and Selective Detection of Cyanide in Aqueous Solution

Abstract

A comprehensive study of the photophysical properties of triethylene glycol monomethyl ether (TEG)‐substituted squaraine dye SQ 1 is presented. SQ 1 exhibits strong absorption and intense fluorescence emission in the far‐red spectral region and high photostability. Interestingly, bis‐tegylated SQ 1 was characterized to exhibit properties different from its tetrahydroxy analog (SQ 2 ), to which we ascribe attenuation of intermolecular interactions as a result of steric hindrance through introduction of two TEG chains adjacent to the squaraine core. The photophysical properties of SQ 1 were also investigated as a function of temperature and pH. In cetyltrimethylammonium bromide (CTAB) micellar media (1.0 m m ), the fluorescence quantum yield of SQ 1 increased dramatically to 0.22, compared with 0.02 in water. Based on this discovery, SQ 1 was found to display excellent sensitivity and selectivity to the presence of cyanide ions (CN – ), with a limit of detection of 1.7 µ m . The hypothesized CN – sensing mechanism was probed, and visual test strips were developed. This work broadens the family of squaraine dyes and demonstrates SQ 1 for use as a fluorescent or visual sensing probe.