Effect of triplet spin dynamics memory in electron-transfer reactions. Fourier transform-electron paramagnetic resonance spectroscopy

Journal Article · Thu Dec 29 04:00:00 EST 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100337a002· OSTI ID:6254227

Angerhofer, A; Toporowicz, M; Bowman, M K; Norris, J R; Levanon, H

Electron-transfer reactions, in ethanol solutions at approx. 243 K, between the photoexcited triplets of two metallotetraphenylporphyrins, ZnTPP and MgTPP (donors), and neutral duroquinone, DQ (acceptor), were studied by selective laser excitation-Fourier transform-EPR spectroscopy. The authors demonstrate that this highly time-resolved EPR differentiates between photochemical processes, occurring early in time, in similar chemical systems. The early spectra (10 ns < /tau//sub d/ < 100 ns) of the DQ/sup /center dot/-/ generated by /sup 3/Zn TPP are totally absorptive, reflecting the out-of-plane active triplet spin state of /sup 3/ZnTPP. On the other hand, the early spectra of the DQ/sup /center dot/-/ radical generated by /sup 3/MgTPP (10 ns < /tau//sub d/ < 400 ns) are totally emissive, reflecting the in-plane active triplet spin state(s) of /sup 3/MgTPP. These results verify that the CIDEP effects due to the triplet mechanism strongly depend on the triplet spin memory of the particular precursor. Qualitative analysis of the temporal changes of the signal intensities results in the following: (i) apparent spin-lattice relaxation (SLR) times of the triplet precursors, i.e., T/sub 1/(/sup 3/ZnTPP) approx. 30 ns, T/sub 1/(/sup 3/MgTPP) approx. 200 ns; (ii) SLR times of the doublet radicals, i.e., T/sub 1/(DQ/sup /center dot/-/) approx. 7-8 ..mu..s, in the presence of ZnTPP; T/sub 1/(DQ/sup /center dot/-/) approx. 2-5 ..mu..s, in the presence of MgTPP; (iii) electron-transfer rates, i.e., k/sub et/(/sup 3/ZnTPP+DQ) approx. 10/sup 9/ M/sup -1/ s/sup -1/, k/sub et/-(/sup 3/MgTPP+DQ) approx. 2 /times/ 10/sup 8/ M/sup -1/ s/sup -1/. They suggest that the different results, ZnTPP vs MgTPP systems, are due to triplet exciplex formation between /sup 3/MgTPP and DQ.

• Research Organization: Argonne National Lab., IL (USA)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 6254227
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:26; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ALCOHOLS
ALKALINE EARTH METAL COMPLEXES
AROMATICS
CARBOXYLIC ACIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
DATA
DYE LASERS
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
ENERGY LEVELS
ETHANOL
EXCITED STATES
EXPERIMENTAL DATA
FOURIER TRANSFORM SPECTROMETERS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
KINETICS
LASERS
LIQUID LASERS
MAGNESIUM COMPLEXES
MAGNETIC RESONANCE
MEASURING INSTRUMENTS
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PORPHYRINS
QUINONES
REACTION KINETICS
RESONANCE
RYDBERG STATES
SPECTROMETERS
ZINC COMPLEXES