Chemical-Modification-Triggered Emergence of Phosphorescence in <i>o</i> -Carborane-Fused Benzophospholes

Herein, we report the synthesis of o-carborane-fused benzophospholes via a palladium-catalyzed method in good to excellent yields. Subsequent modifications at the phosphorus center via oxidation, sulfurization, selenation, and quaternization afforded a series of room-temperature phosphorescent compounds. Different phosphorescence mechanisms emerge by chemical modification: the oxidized product follows a local excitation (LE)-based pathway, while the quaternized (cage-opened) derivatives exhibit a charge transfer (CT)-involved mechanism, as revealed by DFT calculations. Most of these derivatives exhibited a clearly visible afterglow to the naked eye, with the quaternized phosphonium salts demonstrating particularly notable performance. Specifically, compound 3g showed the highest total quantum yield of 24%, while 3i displayed the longest phosphorescence lifetime of 35.39 ms. This work demonstrates that diverse chemical modifications starting from an o-carborane-fused scaffold can activate phosphorescence via distinct mechanisms, providing a new design strategy for tunable room-temperature phosphors without heavy metals or host matrices.