Temperature effects on hydrogen atom transfer (HT) and proton-induced electron transfer (p-ET) via triplet exciplexes in the 1 -naphthol-benzophenone (ROH-BP (or >CO)) and methoxynaphthalene-BP (ROMeBP) systems in acetonitrile-HzO (ACN-H20; 4:l v/v) were studied by 355-nm laser flash photolysis. The HT rate in the ROH-BP system increased with an increase of temperature. The thermodynamic parameters for H T via the triplet exciplex 3(ROH-.>CO)* were obtained: the enthalpy change, AH1 = -2.0 kcabmol-l, and the entropy change, AS1 = -2.4 eu for formation of 3(ROH-.>CO)*; the frequency factor, A , = 7.7 X lo9 s-l, and activation energy, A,??,, = 3.5 kcal-mol-', for intraexciplex HT. The negatively small values of AH1 and AS1 suggest that 3(ROH.->CO)* has a loose sandwichlike structure. The corresponding parameters in the ROMe-BP system were obtained to be A H 1 = -2.2 kcal*mol-1 and A S 1 = -2.8 eu for formation of the triplet exciplex 3(ROMe..->CO)*. In the presence of protons in the ROH-BP system, proton-enhanced H T (p-HT, electron transfer followed by proton transfer) occurs efficiently due to the protonated triplet exciplex, 3(ROH*->C+-OH)*. The p-HT rate increased with an increase of temperature. In the R O M e B P system with protons, formation of the protonated triplet exciplex 3(ROMe...>C+OH)* results in p-ET. The p-ET rate increased with an increase of temperature. The energy state diagrams for H T and p-ET are illustrated.

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