Photochemical decomposition of amidobiphenyls in highly excited triplet states studied by stepwise two-color laser photolysis

Photochemical decomposition of amidobiphenyls (R–AN; R = Me, Et and PhCH2) in highly excited triplet states (Tn with n over 2) was investigated in solution by using stepwise two-color laser photolysis techniques. Upon direct excitation, R–ANs underwent photodecomposition in excited singlet states (S1) with a quantum yield (Φ254) of ca. 0.015. Triplet sensitization using acetone (Ac) was employed for efficient formation of the lowest triplet states (T1) of R–AN and for determining molar absorption coefficients of the Tn ← T1 absorption. No photochemical reactions were found in the T1 state. Upon 355-nm laser flash photolysis of the T1 states of R–ANs, they underwent decomposition. The quantum yields (Φdec) for the decomposition of the molecules in the T1 states were determined to be ca. 0.08. The photodecomposition of the T1 state was proposed to be responsible for CO–N bond cleavage in the Tn state.