CF3‐Inspired Synthesis of Air‐Tolerant 9‐Phosphaanthracenes that Feature Fluorescence and Crystalline Polymorphs

9‐Phosphaanthracene (dibenzo[b,e]phosphorin, acridophosphine) has attracted interest as one of the heavier acenes. Herein, we demonstrate an efficient synthetic process that provides air‐tolerant 1,8‐bis(trifluoromethyl)‐9‐phosphaanthracenes. The sterically encumbered and electron‐withdrawing trifluoromethyl (CF₃) groups are quite advantageous not only to stabilize the intrinsically unstable heavier unsaturated phosphorus atom but also to facilitate construction of the phosphinine skeleton based on a putative increase in aromaticity. The isolated 9‐phosphaanthracenes allowed characterization of their fluorescence functionality and planar heteroanthracene frameworks. The crystal structures of 9‐phosphaanthracenes are remarkably dependent on the aryl substituents at the 10 position; anthryl‐substituted 9‐phosphaanthracene showed unique polymorphs that induced different‐colored crystals.