Comment on “Synthesis and properties of high dielectric constant copolymer of a copper phthalocyanine oligomer grafted to amino-capped polyimide” by L. Chen, Y. Ding, T. Yang, C. Wan and H. Hou, J. Mater. Chem. C, 2017, 5, 8371

Abstract

The purpose of this comment article is to end the myth perpetuated ever since 1982 that the phthalocyanine originating from pyromellitic acid derivatives is a fused, cyclic tetramer (o-CuPc, also often referred to as ‘oligomer’ or ‘polymer’). This material has been attracting attention due to its high dielectric constant and excellent thermal stability, along with inexpensive preparation and facile incorporation into polymers. The resulting electroactive, elastomeric composites have various applications such as electromechanical actuators including artificial muscle and active skin for drag reduction, microelectronic and charge storage devices, and solar cells. As unambiguously demonstrated for the first time in 2012, the product of the reaction reported in 1982 (the structure of which was inadequately characterized at the time) is actually monomeric copper phthalocyanine octacarboxylic acid (m-CuPc). It has also been confirmed that the dielectric constant of pure m-CuPc is essentially the same as the one reported for the assumed “o-CuPc”, and that the high dielectric constant is not a result of extended π-electron delocalization owing to an oligomeric structure, as perpetuated by several recent articles, but proton conduction facilitated by the peripheral carboxylic acid groups.