Excited-state dynamics of highly strained 1,2,3-tri-tert-butylanthraquinone undergoing valence isomerization

Sub-picosecond laser photolysis of the title compound (TBAQ) reveals that a broad absorption band (at 450-750 nm) due to the lowest excited singlet state ((1)TBAQ') decreases with a very short lifetime of 1.7 ps and then an absorption band due to the lowest excited tripler state ((3)TBAQ*) remains as the residual absorption. The fast decay channel of (1)TBAQ* is probably ascribed to the valence isomerization to yield a hemi-Dewar type isomer reported by Miki et al., considering the distorted molecular structure of TBAQ estimated by molecular mechanics calculations.