Isolation and Crystal Structures of Two Singlet Bis(Triarylamine) Dications with Nonquinoidal Geometries

• Published in: Journal of the American Chemical Society Vol. 128; no. 6; pp. 1812 - 1817
• Main Authors: Zheng, Shijun, Barlow, Stephen, Risko, Chad, Kinnibrugh, Tiffany L, Khrustalev, Viktor N, Jones, Simon C, Antipin, Mikhail Yu, Tucker, Neil M, Timofeeva, Tatiana V, Coropceanu, Veaceslav, Brédas, Jean-Luc, Marder, Seth R
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 15.02.2006; Amer Chemical Soc
• Subjects: Aniline Compounds - chemistry; Aniline Compounds - isolation & purification; Cations; Chemistry; Chemistry, Multidisciplinary; Crystallography, X-Ray; Electron Spin Resonance Spectroscopy; Magnetic Resonance Spectroscopy - methods; Molecular Structure; Physical Sciences; Science & Technology; Stilbenes - chemistry; CHARGE STATES; ENERGY; CONJUGATED POLYMERS; RESONANCE; RADICAL-CATION; MOLECULAR-STRUCTURES; AROMATIC-AMINES; ELECTRONIC-STRUCTURE; CONDUCTING POLYMERS; BIPOLARON
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0541534

We report the first structural data for bis(diarylamine) “bipolarons”:  we have isolated and crystallographically characterized salts of the dications obtained by two-electron oxidation of E-4,4‘-bis[di(p-anisyl)amino]stilbene and E,E-2,5-bis{4-[di(p-anisyl)amino]styryl}-3,4-di(n-butoxy)thiophene, [1] 2+ and [2] 2+ respectively. ESR, NMR, and magnetometry suggest both species have singlet ground states. X-ray structures, together with 1H NMR coupling constants for [2] 2+ , indicate geometries in which the bond lengths are shifted toward a quinoidal pattern relative to that in the neutral species, but not to a fully quinoidal extent. In particular, the bond-length alternations across the vinylene bridging groups approach zero. DFT calculations with closed-shell singlet configurations reproduce the observed structures well. Our results indicate that singlet species for which one might expect quinoidal geometries (with differences of ca. 0.1 Å between formally single and double bonds) on the basis of a limiting valence-bond representation of the structure can, in fact, show structures with significantly different patterns of bond lengths.