Effects of Self-Assembly on the Photogeneration of Radical Cations in Halogenated Triphenylamines
Effects of Self-Assembly on the Photogeneration of Radical Cations in Halogenated Triphenylamines
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自组装对卤代三苯胺中自由基阳离子光生的影响
DOI：
10.1021/acs.jpcc.1c04933
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Do, Thanh D.
中科院分区：
文献类型：
--
作者：
Hossain, Muhammad Saddam;Sindt, Ammon J.;Goodlett, Dustin W.;Shields, Dylan J.;O’Connor, Colin J.;Antevska, Aleksandra;Karakalos, Stavros G.;Smith, Mark D.;Garashchuk, Sophya;Do, Thanh D.
我们研究了组装对卤素取代三苯胺 (TPA) 二聚体中电荷转移、电荷重组和自由基阳离子持久性的影响。比较了一系列脲束缚的 TPA 衍生物 1（X = H、Cl、Br 和 I），这些衍生物具有一个在对位被卤素修饰的苯基。脲指导这些衍生物的组装，而卤素取代基影响 TPA 单元的堆积。这些修饰影响 TPA 自由基阳离子的产生和持久性，如电子顺磁共振 (EPR) 光谱监测。通过离子淌度质谱法探讨了溶液和气相中自由基阳离子的形成和降解途径。相比之下，超分子组装增强了这些材料的稳定性以及光生自由基阳离子的持久性，这些自由基阳离子似乎经历了电荷重组而没有降解。在溴代和非卤代衍生物 (1Br,1H) 中观察到大量的自由基阳离子。单分子和氢键二聚体的时间相关密度泛函理论 (TD-DFT) 计算表明，TPA 自由基阳离子的稳定性很大程度上取决于初始光致电荷分离和组装的 TPA 二聚体之间的电子耦合。发现后者在 1I 中比在 1Br 二聚体中强约 7 倍，这可能解释了 1I 自由基的更快的电荷重组和更短的寿命。瞬态吸收 (TA) 光谱和 TD-DFT 能够识别 1Br 的带电物质，并具有动力学痕迹和测量的~80 ns 的寿命。荧光猝灭研究与附近 TPA 之间的初始电荷分离和随后的电荷转移事件一致。未来的探索将集中于这些TPA组件作为空穴传输材料的移动性和应用。
We investigate the effect of assembly on charge transfer, charge recombination, and the persistence of radical cations in halogen-substituted triphenylamine (TPA) dimers. A series of urea-tethered TPA derivatives1(X = H, Cl, Br, and I) are compared, which have one phenyl group modified at theparaposition with a halogen. Ureas direct the assembly of these derivatives while halogen substituents influence the packing of the TPA units. These modifications affect the generation and persistence of TPA radical cations as monitored by electron paramagnetic resonance (EPR) spectroscopy. The formation and degradation pathways of the radical cations in solution and gas phase were probed by ion-mobility spectrometry mass spectrometry. In contrast, supramolecular assembly enhanced the stability of these materials as well as the persistence of their photogenerated radical cations, which appear to undergo charge recombination without degradation. Greater quantities of these radical cations are observed for the bromo and non-halogenated derivatives (1Br,1H). Time-dependent density functional theory (TD-DFT) calculations on single molecules and hydrogen-bonded dimers suggest the stability of TPA radical cations largely depends on initial photoinduced charge separation and electronic coupling between assembled TPA dimers. The latter was found to be about 7 times stronger in1Ithan in1Brdimers, which may explain faster charge recombination and shorter lifetimes of1Iradicals. Transient absorption (TA) spectroscopy and TD-DFT were able to identify the charged species for1Bralong with the kinetic traces and measured lifetime of ∼80 ns. Fluorescence quenching studies are consistent with initial charge separation and subsequent charge transfer event between nearby TPAs. Future exploration will focus on the mobility and application of these TPA assemblies as hole transport materials.
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