Tunable Supramolecular Assembly and Persistent Room-Temperature Phosphorescence in Simple Diarylphosphinic Acids

This study presents persistent room-temperature phosphorescence (pRTP) in simple diarylphosphinic acids 1–3. Their crystalline solids exhibit photoluminescence (PL) lifetimes exceeding 100 ms at ambient conditions and approaching one second at cryogenic temperatures. Incorporation of a hydroxy group (Ar2PO(OH)) enhances intermolecular hydrogen bonding, suppresses nonradiative decay, and improves PL efficiency. These compounds display a tunable supramolecular assembly. Phenyl-substituted 1 forms a zigzag polymer, whereas bulky xylyl- and mesityl-substituted 2 and 3 form dimers. In solution, they exhibit nanosecond fluorescence lifetimes, but in the solid state, enhanced intramolecular interactions and supramolecular organization rigidify the system, enabling pRTP with quantum yields of 15.0%, 10.7%, and 12.8%, respectively. The absence of pRTP in thin films highlights the crucial role of intermolecular interactions. Theoretical studies reveal that excited-state dynamics involve intersystem crossing from S1 to higher triplet states (Tn), followed by internal conversion to T1, and finally, radiative decay to S0, enabling efficient phosphorescence.