Intramolecular electron transfer rate increases

A detailed study of the effect of the medium and temperature on the intramolecular electron transfer rate constant kt in various metal complex systems of the bridge structure has been carried out [25]. The values of kt were found to increase and the activation energy to decrease with increasing polarity of the medium. These effects were accounted for in terms of the modern electron transfer theory (see the case Er > J in Fig. 5 of Chap. 3) by greater changes in the free energy, AG°, due to a higher redox potential of the L/Lr pairs in a more polar medium. 

An occurrence of intramolecular electron transfer shortens the MLCT excited state lifetime 1/t = l/zet -I- 1/to where Tet = lAet This is demonstrated by the the MLCT excited state of [Ru(bpy)3] + [251], the ca 1 ps lifetime of which is shortened to a few tens of picoseconds when a methylviologen di-cation (MV +) is attached to the 4-position of the bpy ligand by a -(CH2) - chain n = 1-8. This is caused by a bpy —> MV + intramolecular electron transfer which occurs from the MLCT excited state. The rate constant of 5.9 x 10 s (ret = 17 ps) has been determined for n = 1, decreasing with increasing n. 

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