Effect of Pyridyl Orientation on the Molecular Conformation and Self-Assembled Morphology of Regioisomeric Diketopyrrolopyrrole Derivatives

5 years ago

Effect of Pyridyl Orientation on the Molecular Conformation and Self-Assembled Morphology of Regioisomeric Diketopyrrolopyrrole Derivatives

Xinrui Miao, Yong Cao, Lei Ying, Wenli Deng, Xiaojun Wang

We reported the synthesis, characterization, and self-assembly of two new regioisomeric π-conjugated chromophores (p-DBPy and d-DBPy) based on pyridyl-flanked diketopyrrolopyrrole (DPP), where the nitrogen atom in the pyridyl was proximal or distal to the central DPP unit. Their solid powders and solutions displayed different colors, especially for p-DBPy, which could be attributed to the conversion of molecular conformation and different intermolecular aggregations. UV–vis spectra demonstrated that the possible intermolecular hydrogen bonding existed in the solution of p-DBPy. Of particular interest is that the morphology of solid powders and thin films for each molecule investigated by SEM and AFM, respectively, were dramatically different owing to different intermolecular interactions and different crystal growth speed. Their spectroscopic and electrochemical properties turned out to be strongly dependent on the orientation of the pyridyl group. DFT calculations were performed to determine the optimized molecular conformation and molecular 3D charge density. At the liquid–solid interface, as visualized by STM, d-DBPy formed a 2D fishbone-like adlayer with linear molecular conformation by the molecule–substrate van der Waals force; however, p-DBPy self-assembled into a fish-scale-like pattern with flexed molecular conformation resulting from intra- and intermolecular hydrogen bonds. Compared with the 2D adlayers, the π–π stacking is another important driving force to determine the morphology of the films. The results demonstrated that understanding the effect of pyridyl orientation along the conjugated core on the molecular conformation and self-assembly is of critical importance for fabricating desired films with special morphology for high-performance organic electronic devices.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06511

DOI: 10.1021/acs.jpcc.7b06511