Two-Dimensional Interface Self-Assembly Of N-Type Organic Semiconductor Molecules

From the wide application of n-type organic semiconductors in optoelectronic materials and electronic devices,it is known that studying the two-dimensional crystallization behavior of semiconductor molecules has guiding significance for the design of optoelectronic devices.However,there are few studies on the self-assembly of n-type semiconductors at the surface or interface.Therefore,the relationship between the molecular structure and the assembly of surface nanostructures is studied,which is conducive to the construction of excellent photoelectric devices.Scanning tunneling microscopy(STM)is a universal technique that can detect nanostructures and dynamic processes at the molecular level.Investigation of semiconductors on the surface or at the interface by STM provides opportunities to observe and understand the mechanism of intermolecular interaction.1.The effect of conjugated backbone dimensions and geometric symmetry on two-dimensional crystallization was studied.Three molecules with the same substituents and molecular geometric symmetry but different conjugated backbone dimensions were designed,and the symmetry of the molecule was changed.The two-dimensional(2D)crystallization of rylene diimide based n-type semiconductors was explored at the liquid–highly oriented pyrolytic graphite interface by means of scanning tunneling microscopy.Rylene diimides with increased aromatic dimensions show different surface crystallization behaviors and distinguished 2D patterns.The surface chirality was also found to be directly affected by the aromatic dimensions.The 2D patterns and the surface chirality could also be tuned by the nature of the solvent.In addition,molecular symmetry was found to be of great important for the formation of long-range ordered 2D monolayers.This investigation highlights the importance of the rational design of molecular dimensions and geometrical symmetry in achieving determined 2D nanopatterns on surfaces,especially for the rylene diimide based ntype semiconductors.2.The impact of halogen???halogen interaction on the 2D crystallization of n-semiconductors has been investigated.A single bromine atom was introduced to perylene-3,4-dicarboxmonoimide(PMI)and explored the effects of the halogen atom on the 2D crystallization at the liquid-solid interface.The 2D nanostructrures and chirality at the liquid-solid interface was monitored by scanning tunneling microscope(STM).Simulations were performed to provide deep insight into the 2D crystallization behaviors.It can be found that PMI and Br-PMI can form well-ordered 2D monolayers at the 1-octanoic acid-HOPG interface.By the introduction of Br atom to the 9-position of PMI,the 2D pattern and chirality were both changed.More densely packing was obtained with the assistance of type I X???X interaction involved with Br atoms.Furthermore,the 2D packing of monolayers was further changed by TBB which provides both type I and II X???X interactions together with X???H—C hydrogen bonds.Hence,single component and binary surface assembly can be changed by introducing halogen???halogen interaction.