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Photoinduced Electron Transfer Reactions by SmI 2 in THF: Luminescence Quenching Studies and Mechanistic Investigations
Author(s) -
Prasad Edamana,
Knettle Brian W.,
Flowers Robert A.
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200401163
Subject(s) - chemistry , excited state , quenching (fluorescence) , photochemistry , electron transfer , photoinduced electron transfer , marcus theory , reaction rate constant , nitrile , luminescence , kinetics , fluorescence , atomic physics , materials science , organic chemistry , physics , optoelectronics , quantum mechanics
Photoluminescence quenching studies of SmI 2 in dry THF were carried out in the presence of five different classes of compounds: ketone, alkyl chloride, nitrile, alkene and imine. The free energy change (Δ G 0 ) of the photoinduced electron transfer (PET) reactions was calculated from the redox potentials of the donor (SmI 2 ) and acceptors. The bimolecular quenching constants ( k q ) derived from the Stern–Volmer experiments parallel the free energy changes of the PET processes. The observed quenching constants were compared with the theoretically derived electron transfer rate constants ( k et ) from Marcus theory and found to be in good agreement when a value of λ =167 kJ mol −1 (40 kcal mol −1 ) was used for the reorganization energy of the system. A careful comparison of the excited state dynamics of Sm II in the solid state to the results obtained in solution (THF) provides new insight in to the excited states of Sm II in THF. The activation parameters determined for the PET reactions in SmI 2 /1‐chlorobutane system are consistent with a less ordered transition state and high degree of bond reorganization in the activated complex compared to similar ground state reactions. Irradiation studies clearly show that SmI 2 acts as a better reductant in the excited state and provides an alternative pathway for rate enhancement in known and novel functional group reductions.