Scanning Tunneling Microscopy Investigation of Two-Dimensional Polymorphism of Structural Isomers

Monolayers of two pairs of structural isomers were deposited on Au(111) and observed via scanning tunneling microscopy in ultrahigh vacuum. We observe exclusively cyclic pentamers of isatin (1H-indole-2,3-dione), whereas its structural isomer, phthalimide (isoindole-1,3-dione), self-assembles primarily into close-packed arrays, with alternate structures that include kinetically locked disordered clusters and tetramer networks. Removal of the phthalimide NH group and its replacement with a CH2 group produces 1,3-indandione, which, despite the loss of the hydrogen-bond donor site, self-assembles into similar structures: close-packed areas and tetramer networks. The equivalent analog for isatin, 1,2-indandione, does not form pentamers and instead forms only close-packed areas and disordered regions. By iteratively altering the chemical structure, we demonstrate the influence that the chemical structure has on the resulting two-dimensional self-assembly.