Center of Spectroelectrochemistry, Department of Electrochemistry and Conducting Polymers, Leibniz Institute for Solid State and Materials Research , D-01069 Dresden, Germany.
J Phys Chem A. 2013 Aug 1;117(30):6702-11. doi: 10.1021/jp405212e. Epub 2013 Jul 22.
The in situ spectroelectrochemical and electron spin resonance (ESR) behavior of the recently prepared N,N,N',N'-tetrakis-(4-diphenylamino-phenyl)-thiophene-2,5-diamine 11 is presented. The results are compared to the ones of the parent 2,5-bis-diphenylamino-thiophene 41 as well as to the corresponding high-molar third dendrimer generation 8 containing the same thiophene-2,5-diamine core. The dendritic compound 11 can be reversibly oxidized in three separated steps to yield the corresponding stable monocation 11(•+), dication 11(2+), and tetracation 11(4+). A well resolved ESR spectrum of the corresponding cation radical 11(•+) with dominating splittings from two nitrogen atoms and two hydrogen atoms was observed at the first oxidation peak similar to 41(•+). The shape of the SOMOs orbitals very well correlates with the proposed distribution of the unpaired electron mainly on the thiophene center and neighboring nitrogen atoms. The spin delocalization on the central thiophene moiety in the monocations for all three model compounds 41(•+), 11(•+), and 8(•+) was confirmed. The computed single occupied molecular orbital (SOMO) for trication 11(•3+) is completely different compared to the SOMO of the corresponding monocation 11(•+), and it confirms a largely delocalized unpaired spin density. Dominating diamagnetic product was determined at the third oxidation peak, confirming the formation of a tetracation by a two electron oxidation of ESR silent dication. The positive charge is fully delocalized over the lateral parts of the molecule leading to the high stability of tetracation 11(4+). The estimated theoretical limit energy of the lowest optical transition S0 → S1 is 2.90 eV, and it can be achieved for the 3D dendrimer generation.
本文介绍了最近制备的 N,N,N',N'-四（4-二苯胺基-苯基）噻吩-2,5-二胺 11 的原位光谱电化学和电子自旋共振（ESR）行为。结果与母体 2,5-双二苯胺基噻吩 41 以及相应的高摩尔第三代树枝状化合物 8（含有相同的噻吩-2,5-二胺核心）进行了比较。树枝状化合物 11 可以可逆地氧化为三个独立的步骤，生成相应的稳定单正离子 11(•+)、二正离子 11(2+)和四正离子 11(4+)。在第一个氧化峰处观察到相应的阳离子自由基 11(•+)的 ESR 谱，其分裂主要来自两个氮原子和两个氢原子，类似于 41(•+)。SOMO 轨道的形状与未配对电子主要分布在噻吩中心和相邻氮原子上的提议非常吻合。在所有三种模型化合物 41(•+)、11(•+)和 8(•+)中，单正离子的噻吩中心的自旋离域得到了证实。与相应的单正离子 11(•+)相比，三正离子 11(•3+)的计算单占据分子轨道（SOMO）完全不同，这证实了未配对自旋密度的大量离域。在第三个氧化峰处确定了主要的抗磁性产物，这证实了通过 ESR 无声二正离子的两电子氧化形成了四正离子。正电荷完全离域在分子的横向部分，导致四正离子 11(4+)的高稳定性。最低光跃迁 S0 → S1 的估计理论极限能量为 2.90 eV，可用于 3D 树枝状化合物。
