Institut de Química Computacional and Departament de Química, Universitat de Girona, Campus de Montilivi, Girona E-17071, Spain.
J Phys Chem A. 2010 Jan 21;114(2):1023-8. doi: 10.1021/jp908764s.
The intramolecular interactions responsible for the planarity observed in poly(3,4-ethylenedioxythiophene) and small 3,4-ethylenedioxythiophene-containing oligomers have been investigated using quantum mechanical methods. Specifically, the relative influence of electron-donating effects, pi-conjugation, and geometric restrictions induced by the cyclic substituent and attractive S...O intramolecular noncovalent interactions, which were proposed to be the most relevant factor for such planarity on the self-rigidification observed in these compounds, have been examined considering a wide number of model compounds. Results evidenced that noncovalent S...O interactions, which were postulated on the basis that the nonbonded distances between sulfur and oxygen atoms belonging to neighboring repeating units are significantly shorter than the sum of the van der Waals radii of sulfur and oxygen, are slightly repulsive destabilizing the planar anti conformation. In contrast, the latter arrangement is favored by the pi-conjugation produced by both geometric restrictions imposed by the cyclic substituent and the electron-donating effects provided by the oxygen atoms attached to positions three and four of each tiophene ring. Therefore, these factors produce gain in aromaticity and favorable electrostatic interactions when the planarity is reached, compensating the Pauli repulsions between the shared electron pairs of the sulfur and oxygen atoms.
使用量子力学方法研究了导致聚（3,4-乙二氧基噻吩）和含小 3,4-乙二氧基噻吩的低聚物中观察到的平面性的分子内相互作用。具体而言，考察了供电子效应、π 共轭以及环状取代基引起的几何限制和吸引 S...O 分子内非共价相互作用对这些化合物中观察到的自刚性的平面性的相对影响，考虑了大量模型化合物。结果表明，基于相邻重复单元中硫和氧原子之间的非键距离明显短于硫和氧的范德华半径之和的假设，非共价 S...O 相互作用略微具有排斥性，从而使平面反式构象不稳定。相比之下，平面式构象是由环状取代基施加的几何限制和氧原子提供的供电子效应产生的 π 共轭所有利于的，这些氧原子分别连接在每个噻吩环的 3 位和 4 位。因此，当达到平面性时，这些因素会产生芳香性的增加和有利的静电相互作用，从而补偿了硫和氧原子的共享电子对之间的 Pauli 排斥。
