Abstract
A highly time-resolved high-frequency/high-field W-band electron paramagnetic resonance (EPR) (ν ~ 94 GHz) is a powerful technique to determine small g anisotropies of transient paramagnetic species. We applied this method to studies of the lowest excited triplet (T1)3 ππ* states in metal complexes such as a platinum (Pt) diimine complex and metal (Zn and Mg) porphines in rigid glasses. From the analyses of time-resolved EPR spectra, g anisotropies were obtained as g z = 2.0048, g x = g y = 2.0035 for Pt(b-iq)(CN)2 (b-iq = 3,3′bi-isoquinoline) and g z = 1.9968, g x = g y = 2.0022 for zinc tetraphenylporphine (ZnTPP). No measurable anisotropies were found for magnesium (Mg) TPP. The g values of the Pt complex are larger than g e (=2.0023, g value of free electron) and that g z of ZnTPP is smaller than g e. These results were interpreted in terms of the nature of the perturbed states: the higher triplet ππ′* state mixes with T1(ππ*) via spin–orbit coupling in ZnTPP. In contrast, the higher triplet dπ* state is involved in this coupling for the Pt complex. Thus, the nature of the perturbed state can be distinguished from the anisotropic g values of the T1(ππ*) state.
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Acknowledgments
We thank Dr. Valery Tarasov at Institute of Chemical Physics, Russian Academy of Sciences, for fruitful discussion and providing us the simulation program of the EPR spectra in the triplet state. This work was supported by Grant-in-Aid for Scientific Researches nr. 18559001 and nr. 19350003 from the Ministry of Education, Science, Culture, and Sports, Japan.
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Yamauchi, S., Tanabe, M., Takahashi, K. et al. Shifts of g Values in the Excited Triplet States of Metal Complexes Studied by Time-Resolved W-band EPR. Appl Magn Reson 37, 317–323 (2010). https://doi.org/10.1007/s00723-009-0100-9
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DOI: https://doi.org/10.1007/s00723-009-0100-9