New preparation of gold-silver complexes and optical fibre environmental sensors based on vapochromic [Au₂Ag₂(C₆F ₅)₄(phen)₂]_n

Complexes [Au₂Ag₂(C₆F₅) ₄L₂]_n, where L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy) or tetrahydrothiophene (tht), have been synthesized by reaction of NBu₄[Au(C₆F₅)₂] with Ag(SO₃CF₃), and the addition of phen or bipy thereafter, or with [Ag(SO₃CF₃)(tht)]. The organometallic vapochromic material [Au₂Ag₂(C₆F₅) ₄(phen)₂]_n is isolated as a powder that is able to detect volatile organic compounds such as acetone even in an aqueous solution. The colour of this vapochromic material changes from bright yellow to white in the presence of different donor solvents such as acetone, methanol or ethanol. For the practical construction of an optical fibre sensor, a sol-gel doped with the vapochromic complex was deposited onto one end of a monomode fibre connected to a coupler. The behaviour of the material was studied at different wavelengths and concentrations of acetone vapours and acetone-water solutions. Changes were detected up to 4 dB in the reflected optical power.