Fast Internal Conversion in Nonfluorescent Carbonyl Anthracenes

The quantum yield of triplet formation (φT) for two nonfluorescent molecules of 9-acetylanthracene and 9-benzoylanthracene was determined with a time-resolved thermal lensing method (TRTL). The value of φT for 9-benzoylanthracene was 0.19 in cyclohexane, indicating that a fast internal conversion process with a rate constant of 4.0 × 1010 s−1 exists in the deactivation from the first excited singlet state (S1).