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

Abstract

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.

Substitution Effects of C-C Triple Bonds on Deactivation Processes from the Fluorescent State of Pyrene Studied by Emission and Transient Absorption Measurements

“…The number of laser pulses in each sample was less than four to avoid excess exposure. The details of the detection system for the time profiles of the transient absorption have been reported elsewhere [27]. The transient absorption spectra were obtained using a USP-554 system from Unisoku, which provides a transient absorption spectrum with one laser pulse.…”

Laser-induced photochemical gas-phase reactions of vibrationally excited triplet molecules

“…The intersystem crossing T1 yeS0, whose rate KTSO is a strongly increasing function of the temperature may be rate determining for slow component decay both at low pressures, when bimolecular processes are not yet impor-12 tant for DF decay and over the pressure range with KI>KTSO. It was shown [1 [1][2][3][4][5][6][7][8][9][10][11][12] that for molecules under study at the same vibrational excitation used the KVT …”

“…During last years the mechanisms of photoreduction for many carbonyl compounds was an active area of research [1][2][3][4] 2. Adding BG leads to a decrease in the time integrated relative intensity of the fast component I, described by the Stern-Volmer relation: la/I l+tPbgZ where I and 1 are the time-integrated intensities ofDF ofthe vapours and their mixtures with BG; 3 is the efficiency of vibrational energy transfer; Z is the rate constant of gas kinetic collisions; z is the lifetime of the vibrationally excited triplet molecules.…”

Hydrogen-Bonding-Induced Electron Transfer from Triplet N,N-Dialkyl-1-naphthylamines to Benzophenone via Triplet Exciplexes

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] However, little attention has been paid to the interactions of triplet-sensitized compounds with the ground state of tripletenergy donors until recently. [22][23][24][25][26][27][28][29][30][31][32] When naphthylammonium ion 22,25 and naphthol 24,26 were employed as triplet energy acceptors from triplet BP in acetonitrile (ACN) or a mixture of ACN and water (4:1 v/v) upon laser excitation at 355 nm, it was found by the production of the benzophenone ketyl radical and the corresponding naphthylamine cation and naphthoxy radicals that hydrogen atom transfer occurred from triplet naphthylammonium ion and naphthol to BP. [22][23][24][25][26][27][28][29][30][31][32] When naphthylammonium ion 22,25 and naphthol 24,26 were employed as triplet energy acceptors from triplet BP in acet...…”