Proton-Conducting Behavior in Flexible Coordination Polymer Free-Standing Membranes

Applying CP to flexible devices remains a considerable challenge because of its brittleness. CP structure of low dimension usually plays a crucial role in deciding on the mechanical flexibility, typical dimensional coordination chain that acts as a rigid frame and the other two directions through many weak molecular interactions. We employed a series layered CP, Cu2(MTCPP) (H4(H2TCPP); 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) (M = Ni(II), Cu(II), Zn(II)), in which a two-dimensional (2D) square grid sheet composed of tetradentate metal porphyrins and paddlewheel-type copper dimers is connected by weak van der Waals forces. These membranes composed with two-dimensional (2D) nanosheets show good orientation and bending tests evaluated their mechanical flexibility. Electrochemical impedance spectroscopy revealed that the in-plane proton conductivities of the membranes show different conductivities due to the difference in the hydration coordination ability of central porphyrin metals. Our present study provides a promising strategy for fabricating new and more advanced 2D CPs without using substrates and additional polymers for photonic devices.