The vapochromic behavior of a mononuclear Pd(II) complex with piroxicam ligands (trans-[Pd(Pir)₂] (Pir⁻ is piroxicam anion)) in the presence of water vapor has been theoretically investigated using the time-dependent density functional theory (TD-DFT). The structure of Pd(II) complex interacting with different number of water molecules (n = 1–5) was optimized, separately. The electronic absorption spectra of the optimized structures were calculated using the TD-DFT method and the changes in the absorption spectrum of complex with the increase in the number of water molecules were followed. Comparison of the absorption spectrum of bare Pd(II) complex with those of its hydrated forms with different numbers of water molecules showed a considerable change in the region of 360–400 nm including the change in the intensity and peak position. The main electronic configurations of the intense absorption lines in the related absorption spectra were determined so that the molecular orbitals involved in these absorption lines were determined. The natural bonding orbital (NBO) analysis was performed to assign the NBOs contributing to these molecular orbitals and to see how the NBO composition of the involved molecular orbitals in the electron excitation change with the number of water molecules. It was observed that the change in the intensity and position of the inter- and intraligand π→π∗ transitions are responsible for the color change. Also, based on the NBO results, the contribution of the electronic transitions involving the Pd(II) ion in the color change of the complex was absent.

加入Pd（II）配合物与吡罗昔康的配体的单核的vapochromic行为（反式- [钯（PIR）₂ ]（PIR ^-使用时间依赖密度泛函理论是吡罗昔康阴离子））在水蒸汽存在已经从理论上研究（TD-DFT）。Pd（II）配合物与不同数量水分子相互作用的结构（n = 1-5）分别进行了优化。利用TD-DFT方法计算了优化结构的电子吸收光谱，并跟踪了配合物随着水分子数目的增加而发生的变化。比较裸露的Pd（II）配合物与水合物的吸收光谱（具有不同数量的水分子）的吸收光谱，可以看到360-400 nm范围内的变化很大，包括强度和峰位置的变化。确定了相关吸收光谱中强吸收线的主要电子构型，从而确定了这些吸收线中涉及的分子轨道。进行了自然键合轨道（NBO）分析，以分配有助于这些分子轨道的NBO，并查看电子激发中所涉及的分子轨道的NBO组成如何随水分子数量的变化而变化。观察到配体间和配体内的强度和位置的变化π → π ∗过渡负责颜色变化。同样，基于NBO结果，不存在涉及Pd（II）离子的电子跃迁对配合物颜色变化的贡献。