Flow Electrochemical Synthesis and Packing Structure-Dependent Photophysical Properties of Sulfur-Containing Polycyclic Aromatic Hydrocarbons

The precise impact of different stacking modes of polycyclic aromatic hydrocarbons (PAHs) on photophysical properties is challenging to delineate due to the complexity of intermolecular interactions. Herein, a highly efficient flow electrochemical synthesis approach for sulfur-containing polycyclic aromatic hydrocarbons (S-PAHs), and based on the S-PAHs compounds, we successfully synthesized polymorphs of S-PAH crystals with different stacking patterns, specifically those belonging to the centrosymmetric P̅1 space group and the noncentrosymmetric P21 space group. The P21 crystal exhibited strong second harmonic generation (SHG) properties, while the P̅1 crystal showed enhanced fluorescence characteristics. The SHG properties of P21 crystals originate from their noncentrosymmetric space group, while the fluorescence enhancement of P̅1 crystals mainly originates from the excimer-induced enhanced emission. The study highlights the tunability of S-PAHs in terms of their optical properties and crystal structures, opening up new avenues for their applications in advanced optical and electronic devices.