The special iron(II) polypyridyl complex substituted by fluorine ([Fe(dftpy)₂]²⁺, dftpy = 6,6″-difluoro-2,2’; 6′2″-terpyridine) with uncommon mixed ground states has been detected recently, but the related explanation and characterization are not enough, especially for the influence of substituents. On the basis of previous studies, the key problem of mixed spin states is expected to be described very well by means of theoretical calculations. In this work, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been carried out to study the characteristics of the excited states in detail. Comparing with the parent complex [Fe(tpy)₂]²⁺ (tpy = 2,2′:6′,2″-terpyridine) and corresponding bromine or chlorine substituted derivates, the ground states of [Fe(dftpy)₂]²⁺ stay around the mixture of singlet state and quintet state, but also there is rare high spin excited state lifetime. Among the halogen substituted complexes, [Fe(dftpy)₂]²⁺ has the shortest MLCT state lifetime of 14.0 ps which has been much longer than subpicosecond lifetime of [Fe(tpy)₂]²⁺. The reason is explored by the combination of electronic structures, absorption properties, extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) and potential energy curves (PECs). We can find that the bond lengths of Fe-N_t play a significant role on the change of metal centered (MC) ground states. With Fe-N_t extended by fluorine atoms, the quintet state becomes lower than the singlet state. Due to the deformation of structures, the interactions between metal and ligands diminish and give rise to weaker d orbital splitting than that of [Fe(tpy)₂]²⁺, but slightly impact the pairwise orbital deformation density characteristics. And the PEC of ⁵MC intersects with ^1,3MC which renders faster non-radiative deactivation through low-lying energy crossing points.

由氟（[Fe（dftpy）₂ ] ₂ ⁺，dftpy = 6,6“ -difluoro-2,2'; 6'2” -terpyridine）取代的特殊铁（II）聚吡啶基配合物具有不常见的混合基态虽然最近检测到，但相关的解释和表征还不够，特别是对于取代基的影响。在以前的研究的基础上，有望通过理论计算很好地描述混合自旋态的关键问题。在这项工作中，已经进行了密度泛函理论（DFT）和时变密度泛函理论（TDDFT）计算，以详细研究激发态的特性。与母体[Fe（tpy）₂ ]比较²⁺（tpy = 2,2'：6'，2''-叔吡啶）和相应的溴或氯取代的衍生物，[Fe（dftpy）₂ ] ²⁺的基态保持在单重态和五重态的混合物附近，很少有高自旋激发态寿命。其中卤素取代的配合物，[Fe（上dftpy）₂ ] ²⁺具有14.0 PS的最短MLCT状态寿命这已经远远长于的的[Fe（TPY）亚皮秒寿命₂ ] ²⁺。通过电子结构，吸收特性，扩展的过渡态与化学价的自然轨道（ETS-NOCV）和势能曲线（PEC）的结合来探索原因。我们可以发现Fe-N的键长_吨玩上金属的变化的角色显著中心（MC）基态。Fe-N _t被氟原子延伸时，五重态比单重态低。由于结构的变形，金属和配体之间的相互作用减少，并导致比[Fe（tpy）₂ ] ²⁺弱的d轨道分裂，但对成对轨道的变形密度特性有轻微的影响。⁵ MC的PEC与^1,3 MC相交，从而通过较低的能量交叉点实现更快的非辐射失活。