Oriented growth of Covalent organic framework (COF) crystals on metal-hydroxides thin film

Covalent organic framework (COF) is a class of porous crystalline material which has been attracted interests for various applications such as separation, electronics and photonics. Controlling a crystallographic orientation of COF over the cm-scale substrate is important to make COF promising candidate for carrier transport materials toward organic electronic devices and host-materials of functional molecules due to the ideal p-electron systems and 1D pore channels. Herein, oriented COF-1 ((C3H2BO)6·(C9H12)) thin films were successfully fabricated by one-pot synthesis method on a unique substrate consisting of aligned metal hydroxides nanobelts. Our idea is based on the use of aligned hydroxyl groups on the surface of metal hydroxides which can react with boronic acid of the COF framework. Detailed X-ray diffraction investigations indicated a crystallographic alignment of the COF-1 crystals, in which boronic ester linkages in COF-1 were found to be parallel to the a-axis of copper hydroxides on the entire surface of the substrate exceeding centimeter scale.