Polycyclic Aromatic Hydrocarbons Containing A Pyrrolopyridazine Core

Polycyclic aromatic azomethine ylides (PAMYs) are versatile building blocks for the bottom-up construction of unprecedented nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs). Here, we demonstrate the 1,3-dipolar cycloaddition between PAMY and 1,4-diphenylbut-2-yne-1,4-dione and the subsequent condensation reaction with hydrazine, which led to unique N-PAHs with a phenyl-substituted pyrrolopyridazine core (PP-1 and PP-2). The molecular structures of pristine PP-1 and tert-butyl-substituted PP-2 were verified by NMR spectroscopy and mass spectrometry. Moreover, the structure of PP-2 was unambiguously elucidated by X-ray single crystal analysis. The optoelectronic properties were investigated by solvent-dependent UV-Vis absorption and fluorescence emission spectroscopy as well as cyclic voltammetry. Additionally, density functional theory (DFT) calculations showed that PP-1 and PP-2 exhibit push-pull behavior. Furthermore, in situ EPR/UV-Vis-NIR spectroelectrochemistry allowed the detailed insight into the spectroscopic properties and spin distribution of radical cation species of PP-2.