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).