Hu Bo, Gahungu Godefroid, Zhang Jingping
Faculty of Chemistry, Northeast Normal University, Changchun 130024, China.
J Phys Chem A. 2007 Jun 14;111(23):4965-73. doi: 10.1021/jp0689215. Epub 2007 May 19.
Theoretical investigations have been performed to explore the optical properties of {[3,5-(CF3)(2)Pz]Cu}3 in monomeric and dimeric forms using TD-DFT approaches. The emission of all complexes originates from the lowest triplet excited-states (T1), and the corresponding emissive states are assigned as the mixture of the metal-centered charge transfer and ligand-to-metal charge transfer. The features of the emission spectrum are clarified in detail. The bulk emission spectrum of complex is mainly determined by the stacked dimers rather than the individual monomers. The predicted maximum emission wavelength (lambda(em)) are in good agreement with experimental values, indicating that the phosphorescence bands can be assigned to two different conformations for the neighboring stacked dimers sharing the same monomer in the complex. Energy transfer from T1 of one stacked dimer to the neighboring one is responsible for the disappearance of the shoulder, leaving only the main peak upon heating. With the aim to reveal the conformational dependence for the triplet excited-state emission spectrum, the optical properties of various stacked dimers with different conformations are investigated by varying the relative arrangements through changing inter-monomer distance or rotational angles for the dimer which is responsible for the main peak emission. Calculation results suggest that the shortest intermolecular Cu...Cu distance plays an important role in the emission spectra of the vertical- and tilting-movement dimers, which is ascribed to the variation of the energy gap for the frontier molecular orbitals involved in the main emitting transition. The blue shift of lambda(em) in parallel-movement and rotational dimers can be traced back to the variation of the mutual spatial orientation. Therefore, the modulation of the extent of movement or rotational angles for stacked dimers by external perturbations creates new possibilities for the design of molecular light-emitting devices.
已采用含时密度泛函理论（TD-DFT）方法进行理论研究，以探索单体和二聚体形式的{[3,5-(CF3)(2)Pz]Cu}3的光学性质。所有配合物的发射均源自最低三重激发态（T1），相应的发射态被指定为金属中心电荷转移和配体到金属电荷转移的混合态。详细阐明了发射光谱的特征。配合物的体发射光谱主要由堆叠二聚体而非单个单体决定。预测的最大发射波长（λ(em)）与实验值吻合良好，表明磷光带可归因于配合物中共享相同单体的相邻堆叠二聚体的两种不同构象。从一个堆叠二聚体的T1到相邻二聚体的能量转移导致肩部消失，加热时仅留下主峰。为了揭示三重激发态发射光谱的构象依赖性，通过改变单体间距离或负责主峰发射的二聚体的旋转角度来改变相对排列，研究了具有不同构象的各种堆叠二聚体的光学性质。计算结果表明，最短分子间Cu...Cu距离在垂直和平移运动二聚体的发射光谱中起重要作用，这归因于主要发射跃迁中涉及的前沿分子轨道能隙的变化。平行运动和旋转二聚体中λ(em)的蓝移可追溯到相互空间取向的变化。因此，通过外部扰动调节堆叠二聚体的运动程度或旋转角度，为分子发光器件的设计创造了新的可能性。
