A series of 12 asphaltene samples extracted from heavy oils and the oxidized bitumen of different origin has been studied with high-frequency W-band (94 GHz) pulsed electron paramagnetic resonance (EPR) spectroscopy. Transverse (T 2e ) and longitudinal (T 1e ) relaxation times of the free radical (FR) and the vanadyl porphyrin (VO 2+ ) were measured for each sample. A significant contribution of the spectral diffusion to T 2e has been revealed and ascribed to the dipole−dipole interaction between the FR and VO 2+ . This indicates that the distance between the FR and VO 2+ does not exceed a few nanometers, which means, in turn, that VO 2+ can participate in construction of the asphaltene aggregates via the intermolecular interactions.

Structural characterization of metalloporphyrins in complex systems such as native hydrocarbons is in the focus of scientific and industrial interests since many years. We describe electron-nuclear double resonance (ENDOR) of crude oil from the well without any additional sample treatment (i.e., in the native environment) in the magnetic field of about 3.4 T and temperature of 50 K by applying microwave pulses at 94 GHz (W-band) and radiofrequency pulses at near the proton Larmor frequencies of 144 MHz to probe the paramagnetic vanadyls. By means of density functional theory (DFT) calculations, ENDOR features are explained and ascribed to certain vanadyl porhyrin structural forms known to be present in crude oil.

Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (VB−). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating VB− centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the VB− centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the VB− spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the VB− spin embedded in the hBN as a probe.

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