Unusual Quartet‐Doublet Phosphorescence from the Phosphaethynyl Radical, CP

We report the first detection of phosphorescence from the phosphaethynyl radical. This rare instance of quartet‐doublet emission, studied here in solid argon, is presumably promoted by efficient intersystem crossing from the originally photoexcited doublet (B2Σ+) to the adjacent second quartet state, 14Δ. Vibronic progressions were traced for the a4Σ+‐X2Σ+ and a4Σ+‐A2Пi systems from their origins up to (v′=0)→(v′′=5) and (v′=0)→(v′′=2) bands, respectively. The measured phosphorescence lifetime is 108 ± 3 ms. CP is generated by photolysis of phosphaethyne (HCP) isolated in solid argon. Phosphorescence of the radical, observed after the B2Σ+‐X2Σ+ photoexcitation, is assisted by an intersystem crossing from B2Σ+ to the adjacent second quartet state, 14Δ. Intense, well‐resolved vibronic progressions were traced for a4Σ+‐X2Σ+ and a4Σ+‐A2Πi emission systems. Phosphorescence lifetime is on the order of 0.1 s.