A new highly selective and sensitive chemodosimeter for dual-channel detection of cyanide in aquo-organic solutions – Solvent effects on photophysical and kinetic properties

Abstract A new bithiophene fluorophore functionalized Schiff base (R) has been synthesized and characterized using NMR, mass and single crystal XRD studies. The probe displays highly selective and sensitive dual channel responses (change of colour and fluorescent enhancement) to cyanide in aqueous DMSO solutions containing 0, 20, 40, 60 and 80% of water. The strong interaction between R and CN¯ is evident from the magnitude of association and binding constants (105 M−1) determined using UV–Vis and fluorescence titrations, respectively. The detection process follows a mechanism involving nucleophilic addition of CN¯ to imine C-atom. The red-shifts observed in the absorption and emission maxima, on increasing the polarity of the solvent, may be due to weak intramolecular charge transfer (ICT) transition exist in the molecule, which is well supported by the distribution of HOMO and LUMO over the entire molecule. The red-shifts found (λem 43 nm), in these solvent systems, upon binding of cyanide are found to be relatively larger than that in free receptor indicating higher dipole moment and charge separation in the excited state. The pseudo-first-order rate constants, for the interaction of R with CN¯, are found to decrease with an increase in polarity of the medium, which is due to stronger solvation of CN¯ in water (than in DMSO) through formation of isoenergetic and isokinetic H-bonds between both C- and N-atoms of cyanide ion and water. Further, the chemodosimeter has successfully been applied to determine CN¯ in real water samples.