Synthesis, photophysical properties, and cyanide detection in aqueous solution of BF2-curcumin dyes

Derivatives of difluoroboron curcumin (BF2-curcumin, BF2-cur(OMe)2, BF2-cur(OTs)2, and BF2-curOTs), were synthesized. All compounds possessed electron donor moieties at both ends of the conjugated π system and an electron acceptor moiety in the middle of the molecules (D–A–D system) and should exhibit different optical properties depending on substituents on the benzene rings. Photophysical properties of curcumin and difluoroboron curcumin derivatives were explored. The electron-withdrawing substituent could decrease the electron acceptability of BF2-acceptor moiety resulting in the hypsochromic shift of both absorption and emission bands. BF2-curcumin and BF2-cur(OMe)2 displayed the positive solvatochromic effect relying predominantly on polarity and polarizability of the solvent. Interestingly, BF2-curcumin showed high selectivity and sensitivity towards cyanide with the detection limits of 22 μM and 0.14 μM measured by visual detection and UV–vis spectrophotometry, respectively. Compared to the original curcumin, BF2-curcumin offered a remarkably promising detection of cyanide with 66-fold enhancement in aqueous media (4:1 of CH3CN/H2O).