Reversible Luminescence Vapochromism and Crystal-to-Amorphous-to-Crystal Transformations of Pseudopolymorphic Cu(I) Coordination Polymers

Four solvent-responsive one-dimensional copper(I) coordination polymers (CPs), namely, {[Cu4I4L(MeCN)(2)]center dot CH2Cl2}(n) (1), {[Cu4I4L(MeCN)(2)]center dot CHCl3}(n) (2), {[Cu4I4L(MeCN)(2)]center dot 0.5p-xylene}(n) (3), and [Cu4I4L(MeCN)(2)](n) (4), were prepared by reaction of CuI with N,N'-bis[2-(cyclohexylthio)ethyl]pyromellitic diimide (L) via self-assembly under varying solvent conditions. CPs 1-4, which are pseudopolymorphic supramolecular isomers derived from solvent molecules, are composed of Cu4I4 cubane clusters. The ligands in CPs 1-3 adopted a synconformation, whereas in CP 4 they were observed in the anti-conformation. This occurred via syn to anti transitions upon heating, followed by exposure to MeCN vapor. In addition, a reversible anti to syn transition was achieved by agitating in mixed organic solvents. It was shown that ligand transition from the syn- to the anti-conformation occurred through crystal-to-amorphous-to-crystal transformations. Furthermore, CPs 1-3 exhibited reversible solvent exchange and crystal transformation by exposure to vapors from volatile organic compounds.