Facile Synthesis of Isomeric Hexacyanopyidine Triphenylene Derivatives

Abstract

Four isomeric hexacyanopyridine triphenylene derivatives were synthesized and characterized. Prepared in three synthetic steps, they were isolated in very good yields (higher than 85%), without flash chromatography. Their identities and purities were proved by high-resolution mass spectrometry (HRMS), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy, and CHN elemental analysis. All compounds show high thermal stability (up to ∼400 °C), as determined by thermogravimetric analyses (TGA). Their absorption and emission properties were also investigated. In line with the presence of aromatic moieties in their structures, they exhibit UV (250–325 nm) π to π* electronic transitions, with slight variations among different isomers. They all show emission profiles similar to those of other triphenylene derivatives (fluorescence band at 350–400 nm), while, interestingly, one of the isomers additionally presents a lower energy (473 nm) broad band, assigned to aggregation phenomena. Single-crystal X-ray diffraction solid-state structures were obtained for two of the compounds, showing that, in the solid state, the columnar organization of triphenylene cores is impeded by the presence of cyanopyridine moieties. Hydrogen bonding analysis illustrates the presence of strong and weak hydrogen bonding in both structures. Hirshfeld surface analysis was additionally performed to better understand the crystal packing interactions.