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-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (C11N7H2-, L', lambda(max) = 549 nm, epsilon(max) = 35 000 M(-1) cm(-1)) has been incorporated as dispersed monomer at a fairly high concentration (c approximate to 0.06 NI) in a thin film (thickness < 1 mu m) of a two-component (poly(methyl methacrylate)/SiO2) glass. L' in the film reacts specifically with Hg2+, as mercury(II) acetate, in water, forming the corresponding monochelated pyrrolizinato complex, > HgL (lambda(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 NH3 in the gas phase, generating the associated reversal color change to violet. These systems have been investigated for future adaptation as optical chemical sensors.