Intervalence Transitions in the Mixed-Valence Monocations of Bis(triarylamines) Linked with Vinylene and Phenylene-Vinylene Bridges

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• 作者：Stephen Barlow ; Chad Risko ; Sung-Jae Chung ; Neil M. Tucker ; Veaceslav Coropceanu ; Simon C. Jones ; Zerubba Levi ; Jean-Luc Bré ; das ; and Seth R. Marder
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：December 7, 2005
• 年：2005
• 卷：127
• 期：48
• 页码：16900 - 16911
• 全文大小：350K
• 年卷期：v.127,no.48(December 7, 2005)
• ISSN：1520-5126

文摘

(E)-4,4'-Bis{bis(4-methoxyphenyl)amino}stilbene, 1, (E,E)-1,4-bis[4-{bis(4-methoxyphenyl)amino}styryl]benzene, 2, and two longer homologues, (E,E,E)-4,4'-bis[4-{bis(4-methoxyphenyl)amino}styryl]stilbene, 3, and (E,E,E,E)-1,4-bis(4-[4-{bis(4-methoxyphenyl)amino}styryl]styryl)benzene, 4, have beenoxidized to their mono- and dications using tris(4-bromophenyl)aminium hexachloroantimonate. Theintervalence charge-transfer (IVCT) band of 1⁺ is narrow and asymmetric and exhibits only weaksolvatochromism. Analysis of this band indicates that 1⁺ is a class-III or class-II/III borderline mixed-valencespecies. In contrast, a broad, strongly solvatochromic IVCT band is observed for 2⁺, indicating that thisspecies is a class-II mixed-valence species. The assignment of 1⁺ and 2⁺ as symmetric class-III andunsymmetric class-II species, respectively, is also supported by AM1 calculations. Hush analysis of theIVCT bands of both 1⁺ and 2⁺ gives larger electronic couplings, V, than for their analogues in which thedouble bonds are replaced with triple bonds. The diabatic electron-transfer distance, R, in 1⁺ can beestimated by comparison of the V estimated by Hush analysis and from the IVCT maximum; it is considerablyless than the geometric N-N separation, a result supported by quantum-chemical estimates of R for 1⁺-4⁺. In 3⁺ and 4⁺, the IVCT is largely obscured by an intense absorption similar to a band seen in thecorresponding dications and to that observed in the monocation of a model compound, (E,E,E)-1-{bis(4-methoxyphenyl)amino}-4-[4-{4-(4-tert-butylstyryl)styryl}styryl]benzene, 5, containing only one nitrogen redoxcenter; we attribute this band to a bridge-to-N⁺ transition. The corresponding dications 1²⁺-4²⁺ show acomplementary trend in the coupling between redox centers: the shortest species is diamagnetic, whilethe dication with the longest bridge behaves as two essentially noninteracting radical centers.