Solution-Processed Large-Area Ultrathin Films of Metal-Coordinated Electron-Rich Adenine-Based Ligand

Using a simple solution-based drop-casting method, we demonstrate formation of a large-area (several tens of micrometers) uniform ultrathin film of a metal-coordinated electron-rich ligand based on modified adenine on a highly oriented pyrolytic graphite surface. On the contrary, the ligand alone crystallized into small domains (a few hundreds of nanometers maximum) on the surface. We show that a delicate balance of coordination bonds and weak H-bonding leads to this unusual uniform growth as supported by scanning tunneling microscopy and atomic force microscopy. The mesoscopic uniformity of the film was understood using X-ray photoelectron spectroscopy, while the microscopic pattern of ultrathin films was corroborated with density functional calculations. Two-dimensional films of electron-rich molecules are of importance in thin-film-based electronic applications, and therefore, their economic processing is also of significance.