Sol−Gel Hybrid Silica Thin Films Doped with 2-(5-Amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide as Optical Chemical Sensors

The metal(II) coordinating anion 2-(5-amino-3,4-dicyano-2 H -pyrrol-2-ylidene)-1,1,2-tricyanoethanide (C 11 N 7 H 2 -, L‘, λ max = 549 nm, ε max = 35 000 M -1 cm -1 ) has been incorporated as dispersed monomer at a fairly high concentration ( c ≈ 0.06 M) in a thin film (thickness < 1 μm) of a two-component (poly(methyl methacrylate)/SiO 2 ) glass. L‘ in the film reacts specifically with Hg 2+, as mercury(II) acetate, in water, forming the corresponding monochelated pyrrolizinato complex, >HgL (λ max = 670 nm). A color change from violet to blue occurs along with this transformation. The >HgL-doped film releases L‘ in the matrix after interaction with small molecules, such as CN - in water or NH 3 in the gas phase, generating the associated reversal color change to violet. These systems have been investigated for future adaptation as optical chemical sensors.