Intermolecular Repulsion through Interfacial Attraction: Toward Engineering of Polymorphs

Abstract

Understanding the formation of crystalline polymorphs is of importance for various applications of materials science. Polymorphism of Schiff base derivatives has recently attracted considerable attention because of its influence on photochromic and thermochromic properties of their 3D crystals. The present investigation extends the study of Schiff base polymorphism to the molecular level by using a combination of scanning tunneling microscopy at the liquid/solid interface and molecular modeling. It is demonstrated that polymorphism of 4-(dodecyloxy)-N-(4-dodecylphenyl)-2-hydroxybenzaldimine (PHB), a Schiff base substituted by alkyl side chains, can occur in 2D crystals when PHB is adsorbed on a surface that is able to exchange charge with the molecule. In particular, on Au(111), PHB molecules self-organize not only into a columnar packing but also in dimer structures. Theoretical and experimental results demonstrate that the dimer-based structure observed on Au(111) originates from molecule/surface interactions, which in turn modify molecule/molecule interactions. The results highlight that the Au(111) substrate is far from being a passive part of the self-assembled system and plays a crucial role in the morphology of 2D polymorphs.

Principles of molecular assemblies leading to molecular nanostructures

“…A number of experimental parameters have already been identified that control the appearance of a certain type of polymorph over another. A non-comprehensive list of these parameters includes the type of solvent [23][24][25][26][27][28][29], the concentration of molecules [30][31][32][33][34][35], the type of substrate [36][37][38][39][40][41], the temperature at which the self-assembly takes place [42][43][44][45] and the thermal history of the sample [46]. How these parameters affect the self-assembly of organic building blocks is the subject of this review, with a special focus on the liquid-solid interface.…”

Polymorphism and Solvatomorphism 2009

“…23 The combination of scanning tunneling microscopy at the liquid-solid interface and molecular modeling has been used to study the formation of polymorphs on gold surfaces, examining the moleculesubstrate interactions that lead to the formation of two-dimensional crystals. 24 Using Schiff base compounds as models for study, it was determined that molecules could self-organize on Au(111) surfaces into columnar and dimer structures, demonstrating that the dimer-based structure was derived from molecule-surface interactions that were capable of modifying molecule-molecule interactions.…”

Thermotropic, Thermo-morphologic, and Thermo-optical Properties of New Smectogenic Calamitic Compounds Containing Imine Linking Groups

“…The synthesis of SA1 was reported in [10], but in our study we used a different synthesis method for this compound. …”