Reversible vapochromic behavior of a porous copper(II) coordination polymer {[ Cu(bhnq)(THF)(2)](THF)}(n) ( 1; THF = tetrahydrofuran) constructed from a flexible hingelike ligand H(2)bhnq [2,2'-bis(3-hydroxy- 1,4-naphthoquinone)] has been investigated by adsorption measurements. The isotherms show large hysteretic and stepwise profiles, suggesting the occurrence of the guest-induced framework transformation. The dynamic coil-like behavior of 1 can be controlled through the change of the hydrogen-bonding interactions caused by the reversible and selective incorporation of guest molecules.