Halide-modulated bistate and tristate fluorescence switching for Cu(i) and Ag(i) complexes

The reaction of a fluorescent trans-chelating ligand L^Ph (where L^Ph = 1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-phenyl-2,3-dihydro-1H-perimidine, QY = 9.7%) with MClO₄ (M = Cu, Ag) can lead to two-coordinate complexes [M(L^Ph)](ClO₄) (M = Cu (1·ClO₄) and Ag (5·ClO₄)). When L^Ph is treated with CuX (X = Cl, Br or I), however, this may lead either to a two-coordinate linear complex [Cu(L^Ph)](CuCl₂) (4·CuCl₂) or to three-coordinate T-shaped complexes [Cu(L^Ph)X] (X = Br (2), I (3)). Moreover, while complex 1·ClO₄ shows a ligand substitution for Cl^- to form 4·CuCl₂, it displays anion coordination for both Br^- and I^- to give 2 and 3, respectively. All of the copper(i) derivatives can readily liberate ligand L^Ph upon reacting with F^-. As such, a cyclic tristate molecular switching system "L^Ph 虠 1·ClO₄ 虠 2 or 3 虠 L^Ph" can be accomplished. For complex 5·ClO₄, the addition of halides X^- (X = Cl, Br, I) results in the abstraction of the silver ions and release of the ligand L^Ph. A simple "L^Ph 虠 5·ClO₄" bistate molecular interconversion may also be constructed. Above all, the complexation of either MClO₄ or CuX with L^Ph can be signalled through different quenching effects, QY = 0.5% for 1·ClO₄, 3.1% for 2, 3.2% for 3, 0.8% for 4·CuCl₂, and 0.3% for 5·ClO₄, to realize facile bistate and tristate fluorescence switching operations.