Department of Chemistry and Biochemistry, University of Mississippi, Oxford, Mississippi 38677, United States.
Interdisciplinary Center for Nanotoxicity, Department of Chemistry, Physics and Atmospheric Sciences, Jackson State University, Jackson, Mississippi 39217, United States.
J Phys Chem A. 2020 Dec 24;124(51):10777-10786. doi: 10.1021/acs.jpca.0c07796. Epub 2020 Dec 11.
Small molecular organic fluorophores have garnered significant interest because of their indispensable use in fluorescence imaging (FI) and optoelectronic devices. Herein, we designed triphenylamine (TPA)-capped donor-acceptor-donor (D-A-D)-based fluorophores having a variation at the heterocyclic donor (D) units, 3,4-ethylenedioxythiophene (), furan (), thiophene (), and 1-methyl-1-pyrrole (), with isoindigo as the core electron acceptor (A) unit. Synthesis of these fluorophores () resulted in four symmetrical dye molecules: , , , and , where TPA functioned as a terminal unit and a secondary electron donor group. Photophysical, electrochemical, and computational analyses were conducted to investigate the effect of heterocyclic donor units on the derivatives. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations provided insightful features of structural and electronic properties of each fluorophore and correlated well with experimental observations. Electron density distribution maps, overlapping frontier molecular orbital diagrams, and highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) electron transfer indicated intramolecular charge transfer (ICT). Theoretical studies confirmed the experimental HOMO energy trend and demonstrated its crucial importance in understanding each heterocycle's donor ability. Stokes shifts of up to ∼178 nm were observed, whereas absorptions and emissions were shifted deeper into the NIR region, resulting from ICT. Results suggest that this isoindigo fluorophore series has potential as a molecular scaffold for the development of efficient FI agents. The studied fluorophores can be further tuned with different donor fragments to enhance the ICT and facilitate in shifting the optical properties further into the NIR region.
小分子有机荧光团因其在荧光成像（FI）和光电设备中的不可或缺的应用而引起了极大的关注。在此，我们设计了基于三苯胺（TPA）封端的给体-受体-给体（D-A-D）的荧光团，其中杂环给体（D）单元有所变化，分别为 3,4-亚乙基二氧噻吩（）、呋喃（）、噻吩（）和 1-甲基-1-吡咯（），以吲哚二酮作为核心电子受体（A）单元。这些荧光团（）的合成得到了四个对称的染料分子：、、、和，其中 TPA 作为末端单元和二级电子给体基团。进行了光物理、电化学和计算分析，以研究杂环给体单元对 衍生物的影响。密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算提供了每个荧光团结构和电子性质的深入特征，并与实验观察结果很好地相关。电子密度分布图、重叠前线分子轨道图以及最高占据分子轨道（HOMO）到最低未占据分子轨道（LUMO）电子转移表明存在分子内电荷转移（ICT）。理论研究证实了实验 HOMO 能量趋势，并证明其在理解每个杂环供体能力方面至关重要。观察到高达约 178nm 的斯托克斯位移，而吸收和发射则进一步向 NIR 区域移动，这是 ICT 的结果。结果表明，该吲哚二酮荧光团系列具有作为高效 FI 试剂的开发的分子支架的潜力。所研究的荧光团可以用不同的供体片段进一步调谐，以增强 ICT 并进一步将光学性质转移到 NIR 区域。
