密度泛函理论/含时密度泛函理论研究 N-杂环卡宾配体铱(III)配合物的几何结构、电子结构、吸收和磷光性质。

DFT/TD-DFT investigation on Ir(III) complexes with N-heterocyclic carbene ligands: geometries, electronic structures, absorption, and phosphorescence properties.

机构信息

State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China.

出版信息

J Comput Chem. 2010 Feb;31(3):628-38. doi: 10.1002/jcc.21360.

DOI:10.1002/jcc.21360

PMID:19551885

Abstract

Iridium(III) complexes with N-heterocyclic (NHC) ligands including fac-Ir(pmb)(3) (1), mer-Ir(pmb)(3) (2), (pmb)(2)Ir(acac) (3), mer-Ir(pypi)(3) (4), and fac-Ir(pypi)(3) (5) [pmb = 1-phenyl-3H-benzimidazolin-2-ylidene, acac = acetoylacetonate, pypi = 1-phenyl-5H-benzimidazolin-2-ylidene; fac = facial, mer = meridional] were investigated theoretically. The geometry structures of 1-5 in the ground and excited state were optimized with restricted and unrestricted DFT (density functional theory) methods, respectively (LANL2DZ for Ir atom and 6-31G for other atoms). The HOMOs (highest occupied molecular orbitals) of 1-3 are composed of d(Ir) and pi(phenyl), while those of 4 and 5 are contributed by d(Ir) and pi(carbene). The LUMOs (lowest unoccupied molecular orbitals) of 1, 2, 4, and 5 are localized on carbene, but that of 3 is localized on acac. The calculated lowest-lying absorptions with TD-DFT method based on Perdew-Burke-Erzenrhof (PBE) functional of 1 (310 nm), 2 (332 nm), and 3 (347 nm) have ML(carbene)CT/IL(phenyl-->carbene)CT (MLCT = metal-to-ligand charge transfer; ILCT = intraligand charge transfer) transition characters, whereas those of 4 (385 nm) and 5 (389 nm) are assigned to ML(carbene)CT/IL(carbene-->carbene)CT transitions. The phosphorescences calculated by TD-DFT method with PBE0 functional of 1 (386 nm) and 2 (388 nm) originate from (3)ML(carbene)CT/(3)IL(phenyl-->carbene)CT excited states, but those of 4 (575 nm) and 5 (578 nm) come from (3)ML(carbene)CT/(3)IL(carbene-->carbene)CT excited states. The calculated results showed that the carbene and phenyl groups act as two independent chromophores in transition processes. Compared with 1 and 2, the absorptions of 4 and 5 are red-shifted by increasing the effective pi-conjugation groups near the C(carbene) atom. We predicated that (pmb)(2)Ir(acac) is nonemissive, because the LUMO of 3 is contributed by the nonemissive acac ligand.

摘要

我们研究了铱（III）配合物与 N-杂环（NHC）配体的相互作用，包括 fac-Ir(pmb)(3)（1）、mer-Ir(pmb)(3)（2）、(pmb)(2)Ir(acac)（3）、mer-Ir(pypi)(3)（4）和 fac-Ir(pypi)(3)（5）[pmb = 1-苯基-3H-苯并咪唑-2-亚基，acac = 乙酰丙酮酸盐，pypi = 1-苯基-5H-苯并咪唑-2-亚基；fac = 面式，mer = 经式]。我们分别采用限制和非限制密度泛函理论（DFT）方法（Ir 原子采用 LANL2DZ，其他原子采用 6-31G）对 1-5 的基态和激发态几何结构进行了优化。1-3 的 HOMO（最高占据分子轨道）由 d（Ir）和 pi（苯基）组成，而 4 和 5 的 HOMO 则由 d（Ir）和 pi（碳烯）组成。1、2、4 和 5 的 LUMO（最低未占据分子轨道）定域在碳烯上，但 3 的 LUMO 定域在乙酰丙酮酸盐上。基于 Perdew-Burke-Erzenrhof（PBE）泛函的 TD-DFT 方法计算得到的 1（310nm）、2（332nm）和 3（347nm）的最低吸收波长具有 ML（碳烯）CT/IL（苯基->碳烯）CT（MLCT = 金属到配体电荷转移；ILCT = 配体内电荷转移）跃迁特征，而 4（385nm）和 5（389nm）的吸收波长则归因于 ML（碳烯）CT/IL（碳烯->碳烯）CT 跃迁。基于 PBE0 泛函的 TD-DFT 方法计算得到的 1（386nm）和 2（388nm）的磷光源于（3）ML（碳烯）CT/（3）IL（苯基->碳烯）CT 激发态，但 4（575nm）和 5（578nm）的磷光源于（3）ML（碳烯）CT/（3）IL（碳烯->碳烯）CT 激发态。计算结果表明，在跃迁过程中，碳烯和苯基基团作为两个独立的发色团发挥作用。与 1 和 2 相比，4 和 5 的吸收峰由于靠近 C（碳烯）原子的有效π共轭基团的增加而发生红移。我们预测（pmb）（2）Ir（acac）是非发光的，因为 3 的 LUMO 由非发光的 acac 配体贡献。