Abstract
Transient behaviors of aromatic ketones (ArK) such as benzophenone and aromatic hydrocarbons (ArH) such as naphthalene (NAP), dibenz[a,h]anthracene (DBA), and chrysene (CHR) in the higher triplet excited state (Tn) were investigated by two-color two-step excitation method using two ns-lasers. The first 355-nm laser generates ArK and ArH in the triplet excited state (T1) which can be subsequently excited to the Tn state. Energy transfer quenching of ArK(Tn) and ArH(Tn) was observed by quenchers (Q) with higher triplet energy than those of ArK(Tn) and ArH(T1) but lower than those of ArK(Tn) and ArH(Tn). From the effect of the Q concentration on the quenching efficiency, the lifetimes of ArK(S0) and ArH(Tn) were estimated. The second energy transfer from Q(T1) to ArK(Tn) or ArH(S0) was observed to occur at the diffusion-controlled rate. No evidence was observed for electron transfer from ArK(Tn) or ArH(Tn) to Q, although the electron transfer is possible to compete with the energy transfer quenching of ArK(Tn) and ArH(Tn) by Q according to the traditional electron and energy transfer theories. It was also found that ArK(Tn) and ArH(Tn) can efficiently induce scission of the halogen-carbon bond of Q such as carbon tetrachloride.
