Selective Population of the n, π* and π, π* Triplet States of 1‐Indanones

The two components of the dual phosphorescence of 1‐indanone (1) and six related ketones (2–7) possess different excitation spectra exhibiting the vibrational progression characteristic of the S0 → S1 (n, π*) transition (shorter‐lived emission) and two bands of the S0 → S2 and 3 (π,π*) 0–0 transitions, respectively. The most favorable intersystem crossing routes are S1 (n, π*) → T (n, π*) and S2,3 (π*) → T (π, π*). Internal conversion to S1 competes more effectively with S (π, π*) → T (π, π*) intersystem crossing only from higher vibrational levels of the S2 and S3 states.