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Measuring optically detected magnetic resonance (ODMR) of diamond nitrogen vacancy centers significantly depends on the photon detectors used. We study camera-based wide-field ODMR measurements to examine the performance in thermometry by comparing the results to those of the confocal-based ODMR detection. We show that the temperature sensitivity of the camera-based measurements can be as high as that of the confocal detection and that possible artifacts of the ODMR shift are produced owing to the complexity of the camera-based measurements. Although measurements from wide-field ODMR of nanodiamonds in living cells can provide temperature precisions consistent with those of confocal detection, the technique requires the integration of rapid ODMR measurement protocols for better precisions. Our results can aid the development of camera-based real-time large-area spin-based thermometry of living cells.

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host αH -PyBTM molecular crystals. The magnetic field (0-14 T), temperature (4.2-20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Real-time temperature monitoring inside living organisms provides a direct measure of their biological activities. However, it is challenging to reduce the size of biocompatible thermometers down to submicrometers, despite their potential applications for the thermal imaging of subtissue structures with single-cell resolution. Here, using quantum nanothermometers based on optically accessible electron spins in nanodiamonds, we demonstrate in vivo real-time temperature monitoring inside Caenorhabditis elegans worms. We developed a microscope system that integrates a quick-docking sample chamber, particle tracking, and an error correction filter for temperature monitoring of mobile nanodiamonds inside live adult worms with a precision of ±0.22°C. With this system, we determined temperature increases based on the worms' thermogenic responses during the chemical stimuli of mitochondrial uncouplers. Our technique demonstrates the submicrometer localization of temperature information in living animals and direct identification of their pharmacological thermogenesis, which may allow for quantification of their biological activities based on temperature., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).)

Intracellular thermometry techniques play an important role in elucidating the relationship between the intracellular temperature and stem cell functions. However, there have been few reports on thermometry techniques that can detect the intracellular temperature of cells during several days of incubation. In this study, we developed a novel quantum thermometric sensing and analysis system (QTAS) using fluorescent nanodiamonds (FNDs). FNDs could label adipose tissue-derived stem cells (ASCs) at high efficiency with 24 h of incubation, and no cytotoxicity was observed in ASCs labeled with less than 500 μg mL -1 of FNDs. The peak of FNDs was confirmed at approximately 2.87 GHz with the characteristic fluorescence spectra of NV centers that could be optically detected (optically detected magnetic resonance [ODMR]). The ODMR peak clearly shifted to the high-frequency side as the temperature decreased and gave a mean temperature dependence of -(77.6 ± 11.0) kHz °C -1 , thus the intracellular temperature of living ASCs during several days of culturing could be precisely measured using the QTAS. Moreover, the intracellular temperature was found to influence the production of growth factors and the degree of differentiation into adipocytes and osteocytes. These data suggest that the QTAS can be used to investigate the relationship between intracellular temperature and cellular functions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Solution EPR and ENDOR studies on the radical cations of three dimeric p-phenylene diamine (PD)-based compounds, the tetraisopropyl-substituted bis-trimethylene-bridged [5,5]paracyclophane 1(iPr)(+) and its tetramethyl- and tetraisopropyl-substituted bis-pentamethylene-bridged [7,7]paracyclophane analogues 3(Me)(+) and 3(iPr)(+), showed that charge is localized on one PD(+) unit on the EPR time scale in all three compounds and determined the nitrogen splitting constants and several of the hydrogen splitting constants for these complex spectra. Rigid glass studies of the diradical dications of 1(iPr)(2+), 3(iPr)(2+), and its tetramethylene-bridged [6,6]paracyclophane analogue 2(iPr)(2+), all of which show significant amounts of thermally excited triplet at low temperature, demonstrated that 1(iPr)(2+) has a singlet ground state but the triplet lies only 0.07 kcal/mol higher in energy, and 3(iPr)(2+) has its triplet lying 0.05 kcal/mol higher in energy than its singlet.

The reactions of 2,4-diaryl-6-tert-butylnitrosobenzenes with 2,2'-azobis[2-(methoxycarbonyl)propane] (5a), 2,2'-azobis(2-cyano-4-methylpentane) (5b), and 2,2'-azobis(2-cyano-4-methyl-4-methoxypentane) (5c) in refluxing benzene gave stable N-tert-alkoxy-2,4-diaryl-6-tert-butylphenylaminyls, which were successfully isolated as radical crystals in 13-52% yields after column chromatography. The radical yields depended on the reaction time and the molar ratio of azo compounds to nitroso compounds. In the same manner, acetyl- and cyano-group-carrying N-tert-alkoxyarylaminyls were generated by the reaction of 2-phenyl-4-(4-acetylphenyl)-6-tert-butylnitrosobenzene and 2-phenyl-4-(4-cyanophenyl)-6-tert-butylnitrosobenzene with 5a and 5b, and they were isolated as radical crystals. X-ray crystallographic analyses were performed for two radicals, and their molecular structures were discussed in detail. The magnetic properties were measured for the two isolated radicals with SQUID in the temperature range 1.8-300 K. One radical showed a weak ferromagnetic interaction (theta = 0.2 K) between the radicals, and the other showed a weak antiferromagnetic interaction (theta = -3.8 K). The ferromagnetic interaction was analyzed based on the X-ray crystallographic structure.

Two N-tert-butoxy-2,6-diaryl-4-(4-pyridyl)phenylaminyls (1) and three N-tert-butoxy-2,6-diaryl-4-(1H-imidazol-1-yl)phenylaminyls (2) were prepared by the reaction of the lithium salts of the corresponding anilines with tert-butyl peroxybenzoate. Although 1 could not be isolated as radical crystals, 2 was successfully obtained as red crystals. The X-ray crystallographic analysis and magnetic susceptibility measurements were performed for one isolated radical.

Four formyl-group-carrying thioaminyl radicals were generated, and one radical could be isolated as radical crystals. Magnetic susceptibility measurements of the isolated radical showed a ferromagnetic regular linear-chain interaction of 2J/k(B) = 3.2 K, which was explained in terms of the X-ray crystallographic results.

N-(2-Pyridylthio)-2,6-diaryl-4-R-phenylaminyls (R = Ph, 4-ClC(6)H(4), MeCO, CN, EtOCO) and N-(4-pyridylthio)-2,6-diaryl-4-R-phenylaminyls (R = Ph, 4-ClC(6)H(4), EtOCO) were prepared and isolated as radical crystals. Their ESR spectra were measured, and the NS and pyridyl nitrogen and anilino meta and pyridyl ortho and para proton hyperfine coupling constants were determined. The spin-density calculations based on the density functional theory were performed by the UBecke 3LYP hybrid method using the STO 6-31G basis set. X-ray crystallographic analyses were performed for three radicals, and their structures were discussed in detail. The magnetic susceptibility measurements were carried out for the nine kinds of isolated radicals with a SQUID magnetometer. One radical showed ferromagnetic coupling (2J/k(B) = 44 K), and the others showed antiferromagnetic behavior. The magnetic interactions observed are explained on the basis of the crystal structures.

N-tert-Butoxy-2,7-di-tert-butyl-1-pyrenylaminyl (4), N-tert-butoxy-2-tert-butyl-1-pyrenylaminyl (5), and N-tert-butoxy-7-tert-butyl-1-pyrenylaminyl (6) free radicals were generated by the reaction of the lithium amides of the corresponding 1-aminopyrenes with tert-butyl peroxybenzoate in THF at -78 degrees C. Although 6 could not be isolated due to the gradual decomposition in solution, 4 and 5 were quite persistent and could be isolated as monomeric radical crystals. The X-ray crystallographic analyses for the isolated free radicals were successfully carried out, indicating that the N and O atoms are almost coplanar with the pyrene ring. The ESR spectra of 4 and 5 were very complex due to the presence of many magnetically unequivalent protons. Therefore, the proton hyperfine coupling (hfc) constants were determined by (1)H ENDOR/TRIPLE resonance spectroscopy. To assign the hfc constants for the pyrene ring protons, a partially deuterated radical, 4-d(4), was prepared and the ENDOR and ESR spectra were measured. To discuss the spin density distribution for 4 and 5 ab initio molecular orbital calculations were performed by the DFT UBecke 3LYP method, using the STO 6-31G basis set. Magnetic susceptibility measurements were carried out for 4 and 5 with a SQUID magnetometer. For 4 a weak antiferromagnetic interaction was observed, and for 5 a very strong antiferromagnetic interaction was observed. The antiferromagnetic interactions were explained by their crystal structures.

The present report describes the first isolation of monomeric N-alkoxyarylaminyls and their chemical and magnetic properties. Reaction of the corresponding lithium amides of 2,4-diaryl-6-tert-butylanilines, 2,6-diaryl-4-tert-butylanilines, or 2,4,6-triarylanilines with tert-butyl peroxybenzoate in THF at -78 degrees C yielded quite persistent N-tert-butoxy-2,4-diaryl-6-tert-butylphenylaminyls (1), N-tert-butoxy-2,6-diaryl-4-tert-butylphenylaminyls (2), and N-tert-butoxy-2,4,6-triarylphenylaminyls (3), respectively, which were isolated in the monomeric form in 17-25% yields. All radicals prepared were oxygen insensitive and thermally very stable. X-ray crystallographic analyses were carried out for two radicals, and it was shown that the N and O atoms are coplanar with the anilino benzene ring. The ESR spectra of 1-3 gave a(N) = 0.984-1.05 and a(H) (anilino meta) = 0.158-0.170 mT (g = 2.0041-2.0043), indicating that the unpaired electron mainly resides on the nitrogen and anilino benzene ring. Magnetic susceptibility measurements for 1 and 3 showed that one radical revealed a weak ferromagnetic interaction and an analysis by the Curie-Weiss law gave 0.3 K as theta. The other radicals examined showed weak antiferromagnetic interactions and theta's were determined to be -0.3 to -1.5 K.

N-[(2-Benzothiazolyl)thio]- (1), N-[(2-benzoxazolyl)thio]- (2), and N-(2-pyrimidylthio)-2,4,6-trisubstituted-phenylaminyls (3) were generated by oxidation of the corresponding amines. Although 2 and 3 were not sufficiently persistent to be isolated, 1 was very persistent and could be isolated as radical crystals. The ESR spectra of nondeuterated and partially deuterated 1-3 radicals were measured, and the spin density distributions were estimated from the hyperfine coupling constants. Ab initio molecular orbital calculations were made for 1 to discuss the spin density distribution in more detail. Single-crystal X-ray crystallographic analysis was performed for one radical. Magnetic properties were measured for isolated four radicals with a SQUID. Two radicals showed ferromagnetic interaction, and analyses of chiT vs T plots with the one-dimensional regular Heisenberg model gave 2J/k(B) = 5.8 and 8.6 K. The remaining two radicals showed antiferromagnetic interaction. Analyses of the chiT vs T plots with the Curie-Weiss law or dimer model gave theta = -1.4 K and 2J/k(B) = -1370 K. The strong antiferromagnetic interaction could be explained in terms of the X-ray crystallographic results.

The preparation, ESR spectra, isolation, and X-ray crystallographic structure of N-(arylthio)-2-tert-butyl-4,6-diarylphenylaminyls (1) and N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyls (2) are described. The aminyls are generated by PbO(2) oxidation of N-(arylthio)-2-tert-butyl-4,6-diarylanilines and N-(arylthio)-4-tert-butyl-2,6-diarylanilines. The kinetic ESR study shows that the aminyls are quite persistent, even in the presence of oxygen, and exist in the individual radical forms. Among the seventeen aminyls prepared, N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-diphenylphenylaminyl (1b), N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-bis(4-chlorophenyl)phenylaminyl (1f), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-diphenylphenylaminyl (2b), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2h), and N-[(3,5-dichlorophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2j) are isolated as radical crystals. The crystallographic structures of 1b and 2b are determined by the X-ray crystallographic analyses. Aminyls 1 and 2 give similar ESR spectra consisting of 1:1:1 triplets with the a(N) values of 0.921-0.948 mT. Deuteration of the phenyl groups on the anilino benzene ring gives rise to a further splitting of the nitrogen 1:1:1 triplet by the anilino meta (0.126-0.138) and phenylthiyl ortho and para protons (0.077-0.096 mT). Upon recording at high gain, one of the partly deuterated aminyls gives satellite lines due to (33)S isotopes at natural abundance from which a(33)(S) is determined to be 0.51 mT. The ESR parameters for 1 and 2 are compared with those for structurally close N-(arylthio)-2,4,6-triarylphenylaminyl and N-(arylthio)-2,4,6-tri-tert-butylphenylaminyl.