Density and Dimensional Control of π-Electrons in Electrostatically Binding Naphthalenediimide Salts

Ayumi Kawasaki, Takashi Takeda, Norihisa Hoshino, Wakana Matsuda, Shu Seki, Tomoyuki Akutagawa

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Abstract

Dianionic bis(benzenesulfonate)-naphthalenediimide (BSNDI2-) formed simple 2:1 cation-anion salts of (NH4 +)2(BSNDI2-) (1), (CH3NH3 +)2(BSNDI2-) (2), (C2H5NH3 +)2(BSNDI2-) (3), [(C2H5)2NH2 +]2(BSNDI2-) (4), and [(C2H5)3NH+]2(BSNDI2-) (5). The thermal stability, crystal structure, electron transport properties, and dielectric response were evaluated for these systems in terms of π-electron density and dimensional crossover from two-dimensional (2D) and one-dimensional (1D) to zero-dimensional (0D) electronic structures. Systematic modification of the counter cations from NH4 + to simple alkylammoniums (CH3NH3 +, C2H5NH3 +, (C2H5)2NH2 +, and (C2H5)3NH+) for BSNDI2- salts affected the packing π-density and dimensionality of NDI π-cores. All single crystals formed alternating cation-anion layers, where the intermolecular interactions in salts 1, 2, 3, 4, and 5 were observed as dense 2D brickstone, 1D column, 1D column, dilute 2D herringbone, and isolated 0D monomer arrangements, respectively. The π-electron occupation percentage in the unit cell of salts 1, 2, 3, 4, and 5 decreased in that order, at 96.2%, 87.8%, 83.8%, 78.8%, and 72.6%, respectively, where the intermolecular π-πinteraction between BSINDI2- anions was gradually diluted on increasing in the cation volume. The transfer integrals between the lowest unoccupied molecular orbital in salts 1-5 clearly indicated a dimensional crossover from 2D to 1D to 0D electronic structures. Flash-photolysis time-resolved microwave conductivity measurements of salts 1, 2, 3, and 4 helped determine the magnitude of electron carrier mobility, which followed the order 1 > 2 ≈ 3 ≈ 4. The dielectric response of salt 1 being an order of magnitude higher than those of salts 2-5 was associated with the protonic conductivity in the NH4 +···-SO3- electrostatic hydrogen-bonding network layer. Simple cation exchange in dianionic BSNDI2- salts conventionally modified the intermolecular π-πinteractions in terms of dimensionality, magnitude, and electron transport properties.

Original languageEnglish
Pages (from-to)1276-1284
Number of pages9
JournalCrystal Growth and Design
Volume20
Issue number2
DOIs
Publication statusPublished - 2020 Feb 5

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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