Substituent Effect on g-Tensor:  Multifrequency ESR Study and DFT Calculation of Polycrystalline Phenoxyl Radicals in Diamagnetic Crystals

Abstract

The substituent effect on the g-tensor of polycrystalline 2,6-di-tert-butyl phenoxyl radical derivatives diluted in diamagnetic crystals was investigated using multifrequency ESR spectroscopy and DFT calculations. It was revealed that the g-tensors of the series of phenoxyl radical derivatives essentially have an orthorhombic symmetry. For some radicals, the hyperfine-splitting tensors from the para groups were resolved. The interpretations and the assignments of the spin-Hamiltonian parameters were confirmed with computer simulations in all bands. The DFT-calculated g-tensors were consistent with the experimental g-tensors. Furthermore, the shifts Delta(g) from the free electron ge were analyzed in details as the sum of three contributions. The spin-orbit interactions were found to be the dominant factor with regard to the Delta(g). With a focus on the s-o term, thus, the relationship of the g-values and the electronic excited states was explained by visualizing the molecular orbitals of the phenoxyl radical derivatives. This study thus showed the very significant potential of the combination of a multi-frequency ESR approach and a DFT calculation to advanced ESR analysis, particularly, g-tensor analysis, even for a powder-sample radical.

Metal Coordinated Phenoxyl Radicals

“…41,42 As an example, the three principal g-tensor components of the tri-tert-butylphenoxyl radical are 2.0072, 2.0043 and 2.0024 (g average = 2.0046). While the g y and g z values are usually similar in all the phenoxyls (and close to the free electron g e value of 2.0023 for g z ), the g x values are strongly dependent on the electrostatic environment around the oxygen atom; when it is hydrogen bonded to a positively charged ammonium group, the g x component can be as low as 2.0064.…”

Formation of Perylenes by Oxidative Dimerization of Naphthalenes Bearing Radical Sources

“…Furthermore, both radicals can be easily stabilized by introducing bulky substituents at the appropriate positions, i. e. the 2-, 4-, and 6-positions where the spin density is high. [29][30][31] Taking advantage of these characteristics of phenols, we prepared naphthalene derivatives substituted with multiple phenol groups as radical sources and intended to utilize their oxidative dimerization reactivity to construct perylene structures. Besides, the reaction mechanism including the characterization of reactive species was discussed using quantum chemical calculations.…”

Intermolecular Hydrogen Bonds between a Radical and a Diamagnetic Matrix: CW-ESR Investigations of 2,6-Di-tert-butyl-4-hydroxymethylphenol

“…At this point, we have systematically interpreted the powderpattern ESR spectra of a series of the phenoxyl radical derivatives with tert-butyl groups at both para positions, including the above radical, and obtained the g-tensors data from X-, Q-, and W-band multi-frequency ESR investigations. 16 The polycrystalline samples of phenoxyl radical derivatives diluted in the corresponding phenol matrix can be prepared either by method 1; UV-irradiation of corresponding phenol matrix, 16 or by method 2; mixing corresponding primary phenol matrix with phenoxyl radical derivative generated from chemical oxidation (PbO 2 oxidation) of corresponding phenol (shown in Figure 1). 15,16 However, in these studies, the X-band ESR spectrum of a polycrystalline radical sample derived from a PbO 2 oxidation of 2,6-di-tert-butyl-4-hydroxymethylphenol in toluene solution in vacuum at room temperature showed a singular pattern, that is to say, anomalously large doublet structure.…”

“…16 The polycrystalline samples of phenoxyl radical derivatives diluted in the corresponding phenol matrix can be prepared either by method 1; UV-irradiation of corresponding phenol matrix, 16 or by method 2; mixing corresponding primary phenol matrix with phenoxyl radical derivative generated from chemical oxidation (PbO 2 oxidation) of corresponding phenol (shown in Figure 1). 15,16 However, in these studies, the X-band ESR spectrum of a polycrystalline radical sample derived from a PbO 2 oxidation of 2,6-di-tert-butyl-4-hydroxymethylphenol in toluene solution in vacuum at room temperature showed a singular pattern, that is to say, anomalously large doublet structure. The generated compound was not evidently the corresponding radical, that is 2,6-di-tert-butyl-4-hydroxymethylphenoxyl radical, from the splitting in the X-band spectrum.…”

“…We previously reported "Pulsed ESR study of electron spin relaxation times of polycrystalline phenoxyl radical derivative in a diamagnetic crystal" in the journal, Solid State Ionics. 17 In that study, the analysis of a temperature dependence of the electron spin relaxation times from the viewpoint of the molecular motions is correct, however, we regarded a radical generated by PbO 2 oxidation as the corresponding radical, since in the case of the other phenols, 15,16 the corresponding phenoxyl radicals can be derived by a similar way. Thus, the present paper also corresponds to the errata of the previous report.…”