Kenneth S. Pitzer Center for Theoretical Chemistry, Chemistry Department, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2011 Mar 28;134(12):124706. doi: 10.1063/1.3569135.
The geometry and magnetization (spin distribution) of the series of flat hexagonal zigzag edged molecules C(6m∗∗2)H(6m) (m = 1,2, ..., 10) in their lowest triplet state (S(z) = 1) has been calculated using density functional theory and a connection established from the known benzene (m = 1) triplets to the triplets and singlet ground state of the largest molecules (m = 9, 10). The triplet state potential energy surface has two minima corresponding to distortions from the ground state geometry, such that CC bonds bisected by a C(2)" rotation axis are either longer or shorter. For both geometries, the spin on the carbon atoms forms a pattern that peaks at the middle of an edge and for large index (m) values is the same (apart from sign) as the edge pattern of the hexagonally sectored singlet radical ground state of the largest member C(600)H(60). This similarity suggests that the singlet ground state of the larger (m = 9, 10) zigzag edged hexangulenes is possibly a hex-radical, in some ways analogous to the di- and higher multiradical ground state of the linear acenes C(4m + 2)H(2m + 4) starting around m ≥ 8 and 9. The spin patterns provide guidance in interpreting the multiradical nature of ground and low lying excited states of large hexangulenes and how magnetism evolves with size in molecules with graphene cores.
一系列平面六方锯齿边缘分子 C(6m∗∗2)H(6m)（m = 1,2,..., 10）在其最低三重态（S(z) = 1）下的几何形状和磁化（自旋分布）已使用密度泛函理论进行了计算，并从已知的苯（m = 1）三重态到最大分子（m = 9, 10）的三重态和单重基态建立了联系。三重态势能表面有两个最小值，对应于偏离基态几何形状的变形，使得通过 C(2)"旋转轴平分的 CC 键要么更长，要么更短。对于这两种几何形状，碳原子上的自旋形成一个在边缘中间达到峰值的图案，对于较大的指数（m）值，与最大成员 C(600)H(60)的六角扇形单重基态的边缘图案相同（除符号外）。这种相似性表明，较大（m = 9, 10）锯齿边缘六方烯的单重基态可能是六重自由基，在某种程度上类似于从 m ≥ 8 和 9 开始的线性并苯 C(4m + 2)H(2m + 4)的双自由基和更高多自由基基态。自旋图案为解释大六方烯的基态和低能激发态的多自由基性质以及具有石墨烯核的分子中磁性能如何随尺寸演变提供了指导。
