Theoretical exploitation of acceptors based on benzobis(thiadiazole) and derivatives for organic NIR-II fluorophores†,Physical Chemistry Chemical Physics

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Theoretical exploitation of acceptors based on benzobis(thiadiazole) and derivatives for organic NIR-II fluorophores†
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2018-07-02 00:00:00 , DOI: 10.1039/c8cp03135e
Bin Zhou _{1,

2,

3,

4,

5} , Zhubin Hu _{1,

2,

3,

4,

5} , Yanrong Jiang _{1,

2,

3,

4,

5} , Cheng Zhong _{6,

7,

8} , Zhenrong Sun _{1,

2,

3,

4,

5} , Haitao Sun _{1,

2,

3,

4,

5}

Affiliation

Small-molecule dyes with fluorescence emission in the second near-infrared (NIR-II) region (1000–1700 nm) have attracted considerable attention in the biomedical and bioimaging fields due to their greater imaging depths, better spatial resolution, and higher signal-to-background ratios. However, currently reported organic NIR-II fluorophores are still limited and there is great demand to develop other novel NIR-II fluorophores besides benzobisthiadiazole (BBT)-based fluorophores. More importantly, there is a lack of an appropriate level of theory capable of providing both efficient and accurate predictions of the electronic structures of organic NIR-II fluorophores. In this work, successful application of time-dependent density functional theory (TDDFT) using optimally-tuned range-separated functionals for calculations of both absorption and fluorescence spectral properties has been demonstrated, compared with the available experimental data. A series of thiadiazole-based acceptors (A) and derivatives based on the D–A–D skeleton are designed coupled with the triphenylamine donor (D). The structure–property relationships for these fluorophores are thus revealed by analyzing their ground (S₀) and excited (S₁) state geometries, frontier molecular orbitals (HOMO and LUMO), HOMO–LUMO energy gaps, oscillator strengths, hole–electron distributions and fluorescence wavelengths. It is suggested that the existence of a hypervalent structure leading to a much lower LUMO level and accompanying significant hole–electron separation plays a key role in the red-shift of fluorescence emission in the NIR-II region. In addition, the substitution of BBT oligomers and analogues as acceptor cores is an efficient way to achieve both red-shifted fluorescence wavelengths and enhanced oscillator strengths. The present work provides a reliable and efficient theoretical tool for predicting the related electronic and spectral properties of organic fluorophores and future screening out of potential candidates for excellent NIR-II molecular fluorophores.

中文翻译：

NIR-II型有机荧光团基于苯并双（噻二唑）及其衍生物的受体的理论研究†

在第二近红外（NIR-II）区域（1000-1700 nm）具有荧光发射的小分子染料，由于它们具有更大的成像深度，更好的空间分辨率和更高的信号强度，因此在生物医学和生物成像领域引起了相当大的关注。到背景的比率。然而，当前报道的有机NIR-II荧光团仍然有限，并且除了基于苯并双噻二唑（BBT）的荧光团之外，对开发其他新型NIR-II荧光团的需求也很大。更重要的是，缺乏能够提供有机NIR-II荧光团的电子结构的有效和准确预测的适当理论水平。在这项工作中，与可用的实验数据相比，已证明成功地应用了时变密度泛函理论（TDDFT），该算法使用最佳调整的范围分隔的泛函来计算吸收和荧光光谱性质。设计了一系列基于噻二唑的受体（A）和基于D–A–D骨架的衍生物以及三苯胺供体（D）。因此，通过分析其荧光基，可以揭示这些荧光基团的结构与性质之间的关系（S₀）和兴奋（S₁）状态几何，前沿分子轨道（HOMO和LUMO），HOMO-LUMO能隙，振荡器强度，空穴-电子分布和荧光波长。有人认为，导致LUMO水平低得多并伴随着明显的空穴-电子分离的高价结构的存在在NIR-II区荧光发射的红移中起关键作用。此外，将BBT低聚物和类似物取代为受体核是获得红移荧光波长和增强振荡器强度的有效方法。本工作为预测有机荧光团的相关电子和光谱性质，以及将来筛选出优秀的NIR-II分子荧光团的潜在候选者提供了可靠而有效的理论工具。

更新日期：2018-07-02

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