Comparisons of Measured Rate Constants with Spectroscopically Determined Electron-Transfer Parameters

Abstract

This work involves comparison of rate constants measured for an intervalence (IV) compound with electrontransfer parameters derived from its optical absorption spectrum. The temperature-dependent rate constants for the radical cation having 3-tert-butyl-2,3-diazabicyclo[2.2.2]oct-2-yl (hydrazine) charge-bearing units attached para to a tetramethylbenzene bridge (1 + ) were previously measured. In this study, resonance Raman is used to calculate the magnitudes of the distortions of normal modes of vibration caused by excitation into the intervalence absorption band. These data produce a vibrational reorganization energy λ v sym of 9250 cm . Zhu-Nakamura theory has been used to calculate preexponential factors for analysis of the previously measured variable temperature optical spectra using quartic-enhanced intervalence bands to extract the total reorganization energy and the intramolecular electron-transfer rate constants for intramolecular electron transfer using electron spin resonance. In contrast to using the Golden Rule equation, separation of λ into solvent and vibrational components is not significant for these data. The Zhu-Nakamura theory calculations produce ln(k/T) versus 1/T slopes that are consistent with the experimental data for electronic couplings that are somewhat larger than the values obtained from the optical spectra using Hush's method.

M2δ to ligand π-conjugation: testbeds for current theories of mixed valence in ground and photoexcited states of molecular systems

“…Furthermore, Zink and Nelson have pointed out that the shape of the electronic absorption bands associated with transitions that give rise to excited state mixed valence can posses significant information concerning this excited mixed valence state. [50][51][52][53][54][55] Given the plethora of spectroscopic techniques and the various types of molecules suitable for study, this is very much a work in progress. However, the examples given below indicate the current level of insight concerning the charge distribution and nature of the singlet and triplet states of selected pairs of M 2 containing complexes of molybdenum and tungsten.…”

%Mixed Valence Compounds as Probes to Determine the Polarity of 1-Butyl-3-methylimadazolium Ionic Liquids

“…24 The λ v for 1 + has been estimated at 10 100 cm -1 from the effect of solvent on ν j max 24 and at 9250 cm -1 from its resonance Raman spectrum. 25 Therefore, the values in Table 2 indicate that λ s in acetonitrile and 4 + PF 6 -is about 4000 (or 4850) cm -1 , and increases 600 cm -1 in 4 + BF 4 -. Figure 4 shows a graphical comparison of ν j max values for 1 + in various solvents 24,26 as well as for solid 1 •+ Ph 4 B -in various matrices.…”

“…The solution spectrum of 1 + has also been determined in several solvents . The λ v for 1 + has been estimated at 10 100 cm -1 from the effect of solvent on ν̄ max 24 and at 9250 cm -1 from its resonance Raman spectrum . Therefore, the values in Table indicate that λ s in acetonitrile and 4 + PF 6 - is about 4000 (or 4850) cm -1 , and increases 600 cm -1 in 4 + BF 4 - .…”

Electron spin resonance

“…The Zhu-Nakamura theory results in linear plots of ln(k/T) versus 1/T in good accord with the experimental data for electronic couplings which are greater than those determined from optical spectroscopy using Hush's method. 132 A review has been published dealing with the role of spin-correlation in the formation, decay and detection of long-lived intramolecular charge-transfer states. 133 In a study of the electron-transfer dynamics in donor-bridge-acceptor molecules of varying bridgelength, a biexponential decay of the total radical pair population was observed.…”