Wavelength-dependent photocycloreversion of the endoperoxides of 1,2,3,4-tetramethylanthracene and 1,2,3,4-tetramethyl-9,10-diphenylanthracene

A pronounced, graduated wavelength dependence of the quantum yield Q c of cycloreversion of the endoperoxides (POs) of 1,2,3,4-tetramethylanthracene (TMAPO) and 1,2,3,4-tetramethyl-9,10-diphenylanthracene (TMDPAPO) was observed. A comparison of the excited singlet state energies of the naphthalene chromophore of TMDPAPO with the steps in the graduation of Q c leads to an evaluation of the cycloreversion efficiencies from each of the upper excited singlet states S n: E c(S 2) = 0.13, E c(S 3) = 0.07 and E c(S 4) = 0.67. These values are compatible with recent results of time-resolved measurements according to which the first C-O bond in PO cycloreversion cleaves within a time domain of about 10 −13 s.