Phosphine→Borane-Functionalized Pyrenes and Anthracenes

The functionalization of polycyclic aromatic hydrocarbons (PAHs) with N→B Lewis pairs, so-called borylative fusion, has recently emerged as a simple and powerful means to modulate their electronic and photophysical properties thanks to the extension of the π system. Herein, we considered a new class of PAHs appended with phosphine→borane Lewis pairs and investigated pyrene as well as anthracene derivatives. In these compounds, strong P→B interactions are enforced geometrically, but the π-system is not extended. Nevertheless, such P→B functionalization was found to significantly impact the optical and electrochemical properties. The P,B-functionalized PAHs display noticeably reduced HOMO-LUMO gaps and enhanced fluorescence. Both the number and position of P→B units turned out to play a significant role.