Stable (Long-Bonded) Dimers via the Quantitative Self-Association of Different Cationic, Anionic, and Uncharged π-Radicals:  Structures, Energetics, and Optical Transitions

Lu, Juwei; Rosokha, Sergiy V.; Kochi, Jay K.

doi:10.1021/ja0364928

Cited by 269 publications

(183 citation statements)

References 97 publications

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“…The calculation reproduced well the peaks in the absorption spectra. Although the quantum chemical calculations on the optical properties of π-dimers are reported in PNL radicals and several ionic radical species, 15, 30, 31 the calculation on π-stacked radical polymers has not been performed. For designing the functional materials based on organic π-radicals, the development of computational analyses on the assemblies of open-shell molecules is indispensable.…”

Section: Discussionmentioning

confidence: 99%

“…5). The timedependent density functional theory (TDDFT) calculation assigned the band as the intermolecular transition within π-dimers, [15][16][17] and the wavelengths are significantly shorter than that in the solid state, suggesting a stacking effect in the column. For the detailed assignment, excited-state calculations of monomers and π-dimers were performed (Supplementary Tables 1-3).…”

Section: Synthesis and Spectroscopymentioning

confidence: 99%

“…The excitation character is the same as that of a π-stacked PNL dimer. [15][16][17] In the tetramer, four SOMOs provide two bonding and two anti-bonding orbitals ( Supplementary Fig. 6), generating four excited states.…”

Section: Synthesis and Spectroscopymentioning

confidence: 99%

“…[12][13][14][15][16][17][18][19] Several PNL derivatives form π-dimers, and exhibit absorption bands around 600 nm. [15][16][17] In a few cases, 1D π-stacking columns are formed with large intermolecular separations of~3.78 (ref. 13) and 3.65 Å, 19 due to bulky protection groups, the latter of which shows a band around 800 nm.…”

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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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Section: Discussionmentioning

confidence: 99%

Section: Synthesis and Spectroscopymentioning

confidence: 99%

Section: Synthesis and Spectroscopymentioning

confidence: 99%

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

et al. 2017

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“…The radical anions are stabilised by spincoupling of unpaired electrons of contiguous tetrahalogenosemiquinone rings forming diamagnetic dimeric species as described by intermolecular association of charged π-radicals. 38,39 Molčanov, K., Kojić-Prodić, B., Babić, D., Žilić, D., Rakvin, B. (2011), "Stabilisation of tetrabromo-and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals", CrystEngComm, Vol.13, No.16, pp.5170-5178.…”

Section: Scheme 1 Oxidation/reduction Reactions Of Tetrahalogenquinonmentioning

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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Reversible Spin Pairing in Crystalline Organic Radicals

Rawson

Hayward

2013

Spin‐Crossover Materials

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The concept of high spin and low spin configurations in d-block complexes is taught in every undergraduate introduction to the coordination chemistry of the transition metals. In this situation the interplay between interelectron repulsion or 'pairing energy' (P E ) and crystal (ligand) field splitting ( ) determines the electronic structure and provides an elegant example of how chemical tuning and modification of the ligand donor set can manipulate electronic structure. When is of a similar magnitude to P E then there is a fine balance between crystal field stabilisation energy (an enthalpic term which favours the low spin configuration) and maximising the number of microstates (an entropic term which favours the high spin configuration). In these cases spin-transitions typically occur between a low temperature enthalpically stabilised low spin configuration and a high temperature entropically favoured high spin configuration. The ability to drive spin-transitions thermally, through light-irradiation or pressure-induced transitions are the focus of the rest of this book. In this chapter we consider organic 'spin-transition' materials whose electronic structures can be manipulated in a conceptually similar but substantially different chemical fashion, that is by examining the fine interplay between inter-electron repulsion (P E ) and promotion energy to a low-lying vacant orbital ( ) within the context of organic chemistry.In order to understand the behaviour of such systems we shall begin with a discussion (Section 8.2) of stable free-radicals and their tendency to associate to form dimers, focusing on computational and experimental studies of the electronic structures of these dimers in the gas phase and in solution. In Section 8.3 we extend these discussions to the solid state and investigate examples in which we observe (i) thermal population of electronic excited states leading to a gradual thermal evolution of paramagnetism upon warming and (ii) firstorder solid state phase transitions in which bond cleavage can lead to abrupt diamagnetic-paramagnetic phase Spin-Crossover Materials: Properties and Applications, First Edition. Edited by Malcolm A. Halcrow.

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Stable (Long-Bonded) Dimers via the Quantitative Self-Association of Different Cationic, Anionic, and Uncharged π-Radicals: Structures, Energetics, and Optical Transitions

Cited by 269 publications

References 97 publications

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

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

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

Reversible Spin Pairing in Crystalline Organic Radicals

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