Effects of substituents on fluorometric detection of cyanide anions by indolium-coumarin dyads.
We synthesized an indolium–coumarin dyad (1) and its derivatives with –Cl (2), –N(CH3)2 (3), or –NO2 (4) substituent, and used them for fluorometric detection of cyanide anions (CN(-)) in aqueous media. All of the dyads exhibit fluorescence enhancement by CN(-) via a nucleophilic interaction of CN(-) with the indolium carbon atoms. Their fluorescence response and selectivity to CN(-), however, depend strongly on the substituents. Ab initio calculation and kinetic analysis were performed to verify the behaviors. Substitution of electron-withdrawing groups (2 and 4) increases the electrophilicity of the indolium carbon. This decreases the activation enthalpy for the nucleophilic interaction with CN(-) and facilitates rapid CN(-) sensing. Compound 4 with very high electrophilicity, however, also promotes nucleophilic interaction with OH(-) in the solution, resulting in decreased CN(-) selectivity. As a result of this, the –Cl-substituted compound 2 containing the indolium carbon with appropriate electrophilicity facilitates rapid (within 1 min) and selective CN(-) detection.
Research Center for Solar Energy Chemistry, and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan. shiraish@cheng.es.osaka-u.ac.jp.
Yasuhiro
Y
Shiraishi
Masaya
M
Nakamura
Takayuki
T
Hirai
D000838:Anions / Q000737:chemistry; D003374:Coumarins / Q000737:chemistry*; D003486:Cyanides / Q000032:analysis*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
D000838:Anions; D003374:Coumarins; D003486:Cyanides; D005456:Fluorescent Dyes; D007211:Indoles; C030374:indole; C030123:coumarin