Self-assemblies of TTF derivatives programmed by alkyl chains and functional groups

Tetrathiafulvalenes (TTFs) are a class of important functional materials whose intermolecular interaction, which will contribute to constructing a supramolecular structure, still needs further understanding. In this study, the self-assembly behavior and structure of a series of TTFs bearing different alkyl chains and substituents were investigated by scanning tunneling microscopy (STM) in combination with density functional theory (DFT) calculations. Contrary to previous reports, herein, a series of benzoic acid-functionalized TTFs (CnTTFCOOH) and pyridine-functionalized TTFs (CnTTFN) with different lengths of alkyl chains have been substituted on the sulfur atom, where n is equal to 8, 10, 14, or 16. Due to the weak intra- and intermolecular interactions, CnTTFN (n = 8 and 10) molecules cannot be observed during STM scanning. For other cases, various self-assembled monolayers with different nanostructures were observed depending on different substituents. The results reveal that the alkyl chains and functional groups on the TTF skeleton synergistically affect the molecular self-assembly process, which results from the synergism of van der Waals, hydrogen bonding, and S⋯S interactions. These results not only help to explain the relationship between structures and properties, but also help to design better molecular structures for various fields.