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.