Università di Modena e Reggio Emilia, Modena, 41125, Italy.
Phys Chem Chem Phys. 2019 Feb 13;21(7):3512-3526. doi: 10.1039/c8cp02845a.
BODIPY dyes are used in a variety of applications because of their peculiar spectroscopic and photo-physical properties that vary depending on the stereochemistry of the functional groups attached to the boron-dipyrromethene core structure. In this work, we have applied several computational methods, adapted for semi-rigid molecules based on the Franck-Condon principle, for the study of the optical properties of BODIPY systems and for the understanding of the influence of functional groups on their spectroscopic features. We have analyzed the electronic spectra of two styryl substituted BODIPY molecules of technological interest, properly taking into account the vibronic contribution. For comparison with recently recorded experimental data in methanol, the vibrationally resolved electronic spectra of these systems were computed using both Time-Independent (TI) and Time-Dependent (TD) formalisms. The first step toward the analysis of optical properties of the styryl modified BODIPYs was a benchmark of several density functionals, to select the most appropriate one. We have found that all benchmarked functionals provide good results in terms of band shape but some of them show strong discrepancies in terms of band position. Beyond the issue of the electronic structure calculation method, different levels of sophistication can be adopted for the calculation of vibronic transitions. In this study, the effect of mode couplings and the influence of the Herzberg-Teller terms on the theoretical spectra has been investigated. It has been found that all levels of theory considered give reproducible results for the investigated systems: band positions and shapes are similar at all levels and little improvements have been found in terms of band shape with the inclusion of Herzberg-Teller effect. Inclusion of temperature effects proved to be challenging due to the important impact of large amplitude motions. Better agreement can be achieved by adopting a suitable set of coordinates coupled with a reduced-dimensionality scheme.
BODIPY 染料因其独特的光谱和光物理性质而被广泛应用，这些性质取决于连接到硼二吡咯甲烷核心结构的官能团的立体化学。在这项工作中，我们应用了几种计算方法，这些方法基于 Franck-Condon 原理，适用于半刚性分子，用于研究 BODIPY 体系的光学性质，并理解官能团对其光谱特征的影响。我们分析了两种具有技术意义的取代苯乙烯基 BODIPY 分子的电子光谱，适当考虑了振子贡献。为了与最近在甲醇中记录的实验数据进行比较，使用时间无关（TI）和时间相关（TD）形式理论计算了这些体系的振动分辨电子光谱。分析苯乙烯基修饰 BODIPY 光学性质的第一步是对几种密度泛函进行基准测试，以选择最合适的泛函。我们发现，所有基准泛函在带形状方面都提供了良好的结果，但其中一些在带位置方面存在较大差异。除了电子结构计算方法的问题外，还可以采用不同的复杂程度来计算振子跃迁。在这项研究中，研究了模式耦合的影响以及 Herzberg-Teller 项对理论光谱的影响。结果表明，对于所研究的体系，所有考虑的理论水平都能给出可重现的结果：在所有水平上，带位置和形状都相似，并且通过包括 Herzberg-Teller 效应，在带形状方面几乎没有改进。由于大振幅运动的重要影响，包括温度效应被证明是具有挑战性的。通过采用合适的坐标集并结合降维方案，可以获得更好的一致性。
