Magneto-Opto-Electronic Bistability in a Phenalenyl-Based Neutral Radical

Itkis, Mikhail E.; Chi, X.; Cordes, A. W.; Haddon, Robert C.

doi:10.1126/science.1071372

Cited by 559 publications

(439 citation statements)

References 14 publications

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“…Electron-coupling of two adjacent tetrahaolgenosemiquinone radicals (characterised as dimers) is also observed in several crystals with π-stacked organic radicals. [58][59][60][61] Table 6 Crystallographic, data collection and structure refinement details…”

Section: Crystal Packing and P-stacking Of The Radical Anionsmentioning

confidence: 99%

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

et al. 2011

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Crystal structures of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates and their solvent-free salts are determined. p-Semiquinone anion radical reveals enhanced aromaticity of the ring compared to the quinone. A pair of p-stacked radical anion (psemiquinone) rings occurs in crystal structures of potassium and rubidium salts of tetrachlorosemiquinone anion acetone solvates and their potassium tetrabromo analogue. The ring centroid separation distances are about 3.2 Å and carbon-carbon contacts between the contiguous rings are 0.3 Å shorter than the sum of van der Waals radii. The spin-coupling of the two unpaired electrons between the two anion radical rings (forming a stacked dimer) correlates with the diamagnetic property of the crystals. Magnetic properties of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates were examined by electron paramagnetic resonance spectroscopy. IntroductionQuinones and semiquinone radicals undergo easily reversible oxidation-reduction reactions and they are excellent electron carriers. Due to influence of the functional groups, quinones may have various values of the standard redox potential. The oxidation potential of the quinones with electron-donating groups such as -OH, is lower, and with electronwithdrawing groups such as -Cl and -NO2, the potential becomes higher. These unique electron properties of quinones are exploited for syntheses, both, in laboratory and by nature in vivo. 1,2 Substituents on the quinoid ring modify electron density affecting oxidation potential and stability of the semiquinone radical (Scheme 1). Perhalogenated benzoquinones are easily reduced and their radicals are rather stable; four electronegative substituents make electron density in the ring significantly lower. Sodium and potassium salts of tetrachlorosemiquinone anion radical were first prepared in 1912 by Torrey and Hunter 3 by reaction of alkali iodide and tetrachloroquinone in acetone. Green salts with formulae NaC 6 C l4 O 2 and KC 6 C l4 O 2 precipitated from cold acetone but quickly decomposed upon heating. During the last fifty years perhalogenosemiquinones were studied by various techniques: EPR, 4-6 UV/Vis 7 and IR/Raman spectroscopy [8][9][10][11] and computational methods. [12][13][14][15] Several charge-transfer systems involving tetrachloro-1,4-benzoquinone (Cl4Q) [16][17][18][19][20] and tetrabromo-1,4-benzoquinone (Br4Q), 21,22 where radical anions can be stabilised under appropriate conditions, have also been designed. A crystallographic study of tetrachlorosemiquinone radical anion-in its well-known potassium salt3-was attempted in a Rudjer Bo_skovi_c Institute, Bijeni_cka 54, HR-10000 Zagreb, Croatia. E-mail: kmolcano@irb.hr Molčanov, K., , "Stabilisation of tetrabromo-and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals", CrystEngComm, Vol.13, No.16, 1973 23 using a film method (Weissenberg camera). However, due to an extremely weak diffraction of poor crystals the authors could only determine unit cells of...

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Section: Crystal Packing and P-stacking Of The Radical Anionsmentioning

confidence: 99%

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

et al. 2011

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“…13) and 3.65 Å, 19 due to bulky protection groups, the latter of which shows a band around 800 nm. 19 π-Stacked structures of π-conjugated PNL dimers (1/2 unpaired electron per PNL unit) [20][21][22] and those of singlet-diradical bisphenalenyls 23 (one unpaired electron per PNL unit) exhibit NIR absorption bands. Bis(dithiazolyl) radicals 24,25 form 1D π-stacks with intercolumnar S•••S and S•••N contacts, showing lowenergy absorption bands around~2500 nm (~0.5 eV).…”

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confidence: 99%

Near-infrared absorption of π-stacking columns composed of trioxotriangulene neutral radicals

et al. 2017

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A long-wavelength photoabsorption of organic molecules has been noticed because of the potential as materials. In addition to the extension of π conjugation, molecular aggregation has been utilized to realize the elongation of absorption wavelength. We report strong near-infrared absorptions of trioxotriangulene neutral radicals in the crystalline state and large-scale theoretical calculations of the radical assemblies interpreting the mechanism of optical properties. Polarized absorption spectra and X-ray diffraction of the crystals clarified that an unusual π-stacking column consisting of π-dimers is key for this absorption. Quantum chemical calculations based on time-dependent density functional theory revealed that the π-dimer shows an electronic transition between frontier orbitals generated by strong coupling of the delocalized singly occupied orbitals of monomers. The interdimer interaction of transition dipole moments, which are parallel to the column, elucidated the increase of absorption wavelength. The divide-andconquer Green function method enabled the large-scale time-dependent density functional theory calculation up to a 60mer, where the maximum number of atoms is 4380, reproducing the near-infrared absorptions of trioxotriangulene crystals. The present method to investigate the mechanism of the long-wavelength photoabsorption is useful for developing organic materials consisting of stable neutral radicals.

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“…In general, the neutral-radical system falls into the Mott insulating states, due to the intrinsic half-filled nature of the valence band consisting of the SOMO. Nevertheless, the relatively high electrical conductivity at room-temperature, s n B10 À 6 -10 À 1 S cm À 1 , has been observed in several types of neutral-radical-based single-component molecular conductors [19][20][21][22][23][24][25][26][27][28][29][30][31][32] . So far, among the purely organic single-component systems, the metallic behaviour has been exclusively achieved under high physical pressure for some neutral-radical conductors 32,33 .…”

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Hydrogen bond-promoted metallic state in a purely organic single-component conductor under pressure

et al. 2013

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Purely organic materials are generally insulating. Some charge-carrier generation, however, can provide them with electrical conductivity. In multi-component organic systems, carrier generation by intermolecular charge transfer has given many molecular metals. By contrast, in purely organic single-component systems, metallic states have rarely been realized although some neutral-radical semiconductors have been reported. Here we uncover a new type of purely organic single-component molecular conductor by utilizing strong hydrogenbonding interactions between tetrathiafulvalene-based electron-donor molecules. These conductors are composed of highly symmetric molecular units constructed by the strong intra-unit hydrogen bond. Moreover, we demonstrate that, in this system, charge carriers are produced by the partial oxidation of the donor molecules and delocalized through the formation of the symmetric intra-unit hydrogen bonds. As a result, our conductors show the highest room-temperature electrical conductivity and the metallic state under the lowest physical pressure among the purely organic single-component systems, to our knowledge.

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Magneto-Opto-Electronic Bistability in a Phenalenyl-Based Neutral Radical

Cited by 559 publications

References 14 publications

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

Near-infrared absorption of π-stacking columns composed of trioxotriangulene neutral radicals

Hydrogen bond-promoted metallic state in a purely organic single-component conductor under pressure

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