Electronic and Optical Properties of Protonated Triazine Derivatives,The Journal of Physical Chemistry C

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Electronic and Optical Properties of Protonated Triazine Derivatives
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-12-04 , DOI: 10.1021/acs.jpcc.0c08812
Michele Guerrini _{1,

2} , Enrique Delgado Aznar ₁ , Caterina Cocchi _{1,

2}

Affiliation

The peculiar electronic and optical properties of covalent organic frameworks (COFs) are largely determined by protonation, a ubiquitous phenomenon in the solution environment in which they are synthesized. The resulting effects are nontrivial and appear to be crucial for the intriguing functionalities of these materials. In the quantum-mechanical framework of time-dependent density-functional theory, we investigate from first principles the impact of protonation of triazine and amino groups in molecular building blocks of COFs in water solution. In all considered cases, we find that proton uptake leads to a gap reduction and to a reorganization of the electronic structure, driven by the presence of the proton and by the electrostatic attraction between the positively charged protonated species and the negative counterion in its vicinity. Structural distortions induced by protonation are found to play only a minor role. The interplay between band gap renormalization and exciton binding strength determines the energy of the absorption onsets: when the former prevails over the latter, a red shift is observed. Furthermore, the spatial and energetic rearrangement of the molecular orbitals upon protonation induces a splitting of the lowest-energy peaks and a decrease of their oscillator strength in comparison with the pristine counterparts. Our results offer quantitative and microscopic insight into the role of protonation in the electronic and optical properties of triazine derivatives as building blocks of COFs. As such, they contribute to rationalize the relationships between structure, property, and functionality of these materials.

中文翻译：

质子化三嗪衍生物的电子和光学性质

共价有机骨架（COF）的特殊电子和光学性质在很大程度上取决于质子化，质子化是在合成它们的溶液环境中普遍存在的现象。所产生的效果是不平凡的，并且对于这些材料的有趣功能至关重要。在时变密度泛函理论的量子力学框架中，我们从第一原理出发研究了水溶液中COFs分子构建基中三嗪和氨基质子化的影响。在所有考虑的情况下，我们发现，质子的存在以及带正电的质子化物质和其附近的负离子之间的静电吸引驱动了质子的吸收，从而导致了间隙的减小和电子结构的重组。发现由质子化引起的结构变形仅起很小的作用。带隙重新归一化和激子结合强度之间的相互作用决定了吸收开始的能量：当前者高于后者时，观察到红移。此外，与原始对应物相比，质子化时分子轨道的空间和能量重排引起最低能量峰的分裂和其振子强度的降低。我们的结果为质子化在三嗪衍生物作为COF的基本组成部分的电子和光学性质中的作用提供了定量和微观的见解。因此，它们有助于合理化这些材料的结构，属性和功能之间的关系。

更新日期：2020-12-17

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