THERMOCHEMICAL PROFILES ON HYDROGEN-ATOM TRANSFER FROM TRIPLET NAPHTHOL AND PROTON-INDUCED ELECTRON-TRANSFER FROM TRIPLET METHOXYNAPHTHALENE TO BENZOPHENONE VIA TRIPLET EXCIPLEXES STUDIED BY LASER FLASH-PHOTOLYSIS
M. Yamaji et al., THERMOCHEMICAL PROFILES ON HYDROGEN-ATOM TRANSFER FROM TRIPLET NAPHTHOL AND PROTON-INDUCED ELECTRON-TRANSFER FROM TRIPLET METHOXYNAPHTHALENE TO BENZOPHENONE VIA TRIPLET EXCIPLEXES STUDIED BY LASER FLASH-PHOTOLYSIS, Journal of physical chemistry, 98(28), 1994, pp. 7014-7021
Temperature effects on hydrogen atom transfer (HT) and proton-induced
electron transfer (p-ET) via triplet exciplexes in the l-naphthol-benz
ophenone (ROH-BP (or >CO)) and methoxynaphthalene-BP (ROMe-BP) systems
in acetonitrile-H2O (ACN-H2O; 4:1 v/v) were studied by 355-nm laser f
lash photolysis. The HT rate in the ROH-BP system increased with an in
crease of temperature. The thermodynamic parameters for HT via the tri
plet exciplex (3)(ROH-->CO) were obtained: the enthalpy change, Delta
H-1 = -2.0 kcal.mol(-1), and the entropy change, Delta S-1 = -2.4 eu
for formation of 3(ROH-->CO); the frequency factor, A(ex) = 7.7 x 10(
9) s(-1) and activation energy, Delta E(ex) = 3.5 kcal.mol(-1), for in
traexciplex HT. The negatively small values of Delta H-1 and Delta S-1
suggest that (3)(ROH-->CO) has a loose sandwichlike structure. The c
orresponding parameters in the ROMe-BP system were obtained to be Delt
a H-1 = -2.2 kcal.mol(-1) and Delta S-1 = -2.8 eu for formation of the
triplet exciplex (3)(ROMe-->CO). In the presence of protons in the R
OH-BP system, proton-enhanced HT (p-HT, electron transfer followed by
proton transfer) occurs efficiently due to the protonated triplet exci
plex, (3)(ROH-->C+OH). The p-HT rate increased with an increase of te
mperature. In the ROMe-BP system with protons, formation of the proton
ated triplet exciplex 3(ROMe-->C+OH) results in p-ET. The p-ET rate i
ncreased with an increase of temperature. The energy state diagrams fo
r HT and p-ET are illustrated.