Cerezo Javier, Avila Ferrer Francisco J, Santoro Fabrizio
CNR-Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organo Metallici (ICCOM-CNR), UOS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy.
Phys Chem Chem Phys. 2015 May 7;17(17):11401-11. doi: 10.1039/c5cp00370a.
We simulate from first-principles the absorption spectra of five structure-related coumarin derivatives utilized in dye sensitized solar cells (DSSCs), investigating the vibronic and solvent contributions to the position and width of the spectra in ethanol. Ground and excited state potential energy surfaces (PESs) are modeled by Density Functional Theory (DFT) and its time-dependent (TD) expression for the excited state (TD-DFT). The solute vibronic structure associated with the spectrum is calculated by a TD formalism, accounting for both Duschinsky and temperature effects, while solvent inhomogeneous broadening is evaluated according to Marcus' theory, computing the solvent reorganization energy by the state-specific implementation of the polarizable continuum model (PCM) within TD-DFT. We adopted both the standard hybrid PBE0 and the range separated CAM-B3LYP functionals showing that the latter performs better both concerning the vibronic and solvent-induced contributions to the absorption lineshape. The different predictions of the two functionals are then rationalized in terms of the charge transfer (CT) character of the transitions showing that, in this class of compounds, it is strongly dependent on the nuclear structure. Such a dependence introduces a bias in the PBE0 PES that has a drastic impact on the vibronic spectra. We show that both the intrinsic vibronic structure and the solvent broadening play a relevant role in differentiating the absorption width of the five dyes. In this sense, our results provide a guide to understand the sources of spectral broadening of this family of dyes, a valuable help for a rational design of new molecules to improve DSSC devices.
我们从第一性原理出发，模拟了用于染料敏化太阳能电池（DSSC）的五种结构相关香豆素衍生物的吸收光谱，研究了乙醇中振动和溶剂对光谱位置及宽度的贡献。基态和激发态势能面（PESs）采用密度泛函理论（DFT）及其激发态的含时（TD）表达式（TD-DFT）进行建模。与光谱相关的溶质振动结构通过TD形式计算，同时考虑了杜施insky效应和温度效应，而溶剂非均匀展宽则根据马库斯理论进行评估，通过在TD-DFT中极化连续介质模型（PCM）的状态特定实现来计算溶剂重组能。我们采用了标准的杂化PBE0和范围分离的CAM-B3LYP泛函，结果表明后者在振动和溶剂诱导对吸收线形的贡献方面表现更好。然后根据跃迁的电荷转移（CT）特性对这两种泛函的不同预测进行了合理化解释，结果表明，在这类化合物中，电荷转移特性强烈依赖于核结构。这种依赖性在PBE0势能面中引入了偏差，对振动光谱产生了巨大影响。我们表明，固有振动结构和溶剂展宽在区分这五种染料的吸收宽度方面都起着重要作用。从这个意义上讲，我们的结果为理解这类染料光谱展宽的来源提供了指导，对合理设计新分子以改进DSSC器件有很大帮助。
