Determination of the Lifetime of the Second Excited Triplet State of Anthracenes

Article abstract of DOI:10.1021/j100178a013

The lifetimes of the T₂ states of several substituted anthracenes have been determined using competitive quenching techniques in combination with laser flash photolysis.Thus, Stern-Volmer quenching of 1,3-octadiene yields different slopes depending on whether the triplet or the fluorescence yield are monitored.The difference, which can be treated quantitatively, is the result of T₂ quenching by the diene.Typical T₂ lifetimes are ca. 23, 11, and 3 ps for 9,10-dichloroanthracene, anthracene, and 1-methylanthracene, respectively.It is shown that consideration of time-dependent diffusional quenching is essential and that discrepancies with earlier studies may largely reflect the contribution from this process, as well as S₁ quenching by typical T₂ quenchers.Theoretical calculations suggest that interactions of T₂ with the nearby T₃ state may play a key role in determining the rate of internal conversion to T₁.Calculations have been carried out for the methyl derivatives; these, while consistent with experiments, tend to reflect the limitations of current theory in the interpretation of substituent effects.