Triple Phosphorescence and Rapid Spin Flip Mediated by Ultrafast Electron Transfer in a Spirocyclic Molecule

We report triple phosphorescence emitted by sp3-C linked dimethylaniline-phthalide dyads (DMA-PD) and explore its mechanisms. In 77 K organic solvent glasses, ultrafast photoinduced electron transfer populates in DMA-PD a charge-separated state (CSS), with a DMA cation and PD anion. Depending on glass polarity, the anion is produced in one of two forms, with a closed or open lactone ring. The closed ring CSS deactivates to a locally excited or charge transfer triplet, while the open ring form relaxes to the zwitterion triplet state. All three triplets have different electronic configurations and are formed in different, kinetically noncorrelated intersystem crossing (ISC) mechanisms, particularly rapidly in methylcyclohexane glass (kisc ≥ 2.3 × 1011 s-1). Our findings open the way to structural control over ultrafast triplet generation, population of multiple emissive triplet states in a single molecule, and probing heterogeneous structures and dynamics of supercooled liquids and glasses.