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 SQ1 is presented. SQ1 exhibits strong absorption and intense fluorescence emission in the far‐red spectral region and high photostability. Interestingly, bis‐tegylated SQ1 was characterized to exhibit properties different from its tetrahydroxy analog (SQ2), 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 SQ1 were also investigated as a function of temperature and pH. In cetyltrimethylammonium bromide (CTAB) micellar media (1.0 mm), the fluorescence quantum yield of SQ1 increased dramatically to 0.22, compared with 0.02 in water. Based on this discovery, SQ1 was found to display excellent sensitivity and selectivity to the presence of cyanide ions (CN–), with a limit of detection of 1.7 µm. The hypothesized CN– sensing mechanism was probed, and visual test strips were developed. This work broadens the family of squaraine dyes and demonstrates SQ1 for use as a fluorescent or visual sensing probe.

Synthetic β‐Cyclodextrin Dimers for Squaraine Binding: Effect of Host Architecture on Photophysical Properties, Aggregate Formation and Chemical Reactivity

“…Eight squaraine guests (compounds 4 – 11 , Figure ) were synthesized via the condensation of squaric acid and N ‐substituted N ‐methylanilines following a general procedure previously reported for the synthesis of similar species . Six of the squaraines reported herein incorporate straight‐chain alkyl groups from n ‐butyl to n ‐nonyl (compounds 4 – 9 ), with a cyclic substituent (compound 10 ) and a tert ‐butyl‐substituted benzene (compound 11 ) included in the other two structures (Figure ).…”

Squaraine-Based Optical Sensors: Designer Toolbox for Exploring Ionic and Molecular Recognitions

“…The addition of the nucleophile to the squaraine core produced non-emissive species, while the addition of appropriate analytes led to the elimination of the nucleophile, restored the squaraine conjugation, and regenerated the original photophysical properties (Figure 6A). Squaraine-based chemodosimeters that are responsive to various nucleophilic analytes have been reported, including thiols (Figure 6B) [103][104][105][106], nitrogen-containing nucleophiles, such as amines and hydrazine (Figure 6C) [107], as well as cyanide ion (Figure 6D) [108,109]. It should be noted that thiol and hydrazine additions to squaraines could typically be reversed by the addition of thiophilic metal ions or aldehydes, respectively.…”

“…However, in neat CH3CN, SQS35 exhibited excellent selectivity towards CNover other nucleophilic anions, such as F − and AcO − [108]. Yet, it Representative structures of the following SQSs that showed sensitivity towards thiols (B): SQS33 [103], SQS34 [104], SQS35 [105], SQS36 [106]; the following to hydrazine and amines (C): SQS37 [107]); the following to cyanide ion (D): SQS38 [108], SQS39 [109]).…”

“…Some examples of nucleophile-sensitive SQSs. ON-OFF-ON relay of nucleophile-specific chemodosimeter (A).Representative structures of the following SQSs that showed sensitivity towards thiols (B): SQS33[103], SQS34[104], SQS35[105], SQS36[106]; the following to hydrazine and amines (C): SQS37[107]); the following to cyanide ion (D): SQS38[108], SQS39[109]).…”

Squaraine Dyes for Photovoltaic and Biomedical Applications

“…SQs possess unique properties for sensing of various factors such as temperature, [ 114 ] pH, [ 115 ] ions, [ 116 ] and biomolecules [ 117 ] which are important in biological systems attributed to their molecular structures that make various reactions with external environment. Especially, SQs can form folded complex structure known as “H‐aggregates” [ 118 ] which indicates the H‐shape of SQ‐based molecules from the folding induced by binding between metal ions (not monovalent ions) and electron‐rich moieties such as polyether, and then results in color change and fluorescence quenching when they bind metal ions and species of ions that react with SQs that are dependent on the structures of SQs.…”