Using Molecular Level Modification To Tune the Conductivity of Graphene Papers

Graphene's excellent electrical conductivity benefits from its highly conjugated structure. Therefore, the manipulation of graphene's electronic and mechanical properties should be realized by controlled destruction of its in sheet conjugation. Here, we report the manipulation of the conductivity of graphene papers, at the molecular level, via either covalent bonding or pi-pi stacking interactions using either monofunctional or bifunctional molecules. The graphene papers can be tailored with controllable conductivity from around 100 to below 0.001 S/cm. The controlled destruction of the in-sheet graphene conjugation system using monoaryl diazonium salts (MDS) resulted in a tunable decrease in the graphene paper conductivity. However, when the graphene was modified with bifunctional aryl diazonium salts (BDS), a more subtle decrease in conductivity of the graphene papers was observed It is suggested that the modification of the graphene with the bifunctional BDS linker showed more subtle changes in conductivity because of the between sheet electron communication, thus boosting the collective graphene paper conductivity. Consequently, a bipyrene terminal molecular wire (BPMW) was also synthesized and used to modify the graphene sheets via pi-pi stacking interactions. The BPMW afforded graphene papers with better electrical conductivity than those modified with either MDS or BDS molecules.