A Dual Responsive Fluorescent Probe Exhibiting ICT Based Colorimetric and Fluorimetric Detection of Cyanide.

2-(pyridin-4-yl)-8H-thieno[2,3-b] indole (ITP) fluorescent probe has been synthesized and utilized as a ratiometric sensor for cyanide anion. The color change upon the addition of cyanide anion is easily noticeable with naked eyes. The greater difference between the absorption and emission spectrum due to the inclusion of cyanide is attributed to the enhanced intramolecular charge transfer (CT) by hydrogen bonding of CN¯ with ITP, which greatly increased the electron density on the donor thieno[2,3-b] indole. The cyanide sensing mechanism is further confirmed by 1H NMR and DFT studies. Further, ITP exhibited aggregation-induced emission enhancement in DMSO:water. In addition, the presence of pyridine moiety in ITP is helpful for acid sensing.