Zwitterists: Photo-patternable Polymer Zwitterions for Interfacial Dipole Doping of Monolayer Graphene

Electronic modulation of 2D materials with dipole-rich zwitterionic polymer coatings holds promise for enhancing electronic device performance. Although significant shifts in the work function (WF) of graphene have been induced by a variety of zwitterionic polymers, the influence of zwitterion structure is not well understood. We built the polymeric "zwitterist" (a portmanteau from zwitterion and photoresist) platform to understand how steric footprint impacts the WF modulation of graphene with polymer zwitterions via dipole doping. A series of zwitterionic sulfobetaine-based random copolymers with variable substituents and photo-crosslinkable benzophenone moieties was synthesized and utilized to prepare negative-tone resists for spatial WF engineering of graphene. Of the polymers investigated, the piperidinyl-substituted version possessing the bulkiest steric group induced the largest WF reduction as observed from spectroscopic measurements and theoretical calculations. The "zwitterist" design was extended to fluorinated polymer zwitterions to understand the individual contribution of two types of dipoles within the side chains: choline phosphate (zwitterion) and fluorinated alkyl groups. This platform will inspire the discovery of new and simple WF engineering approaches.