Samuthirapandi Kiruthika, Durairaj Pandiselvi, Sarkar Sunandan
Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, India.
ACS Appl Mater Interfaces. 2024 Jun 19;16(24):31045-31055. doi: 10.1021/acsami.4c02443. Epub 2024 Jun 10.
Photoexcited charge transfer dynamics in CdSe quantum dots (QDs) coupled with carbazole were explored to model QD-molecule systems for light-harvesting applications. The absorption spectra of QDs with different sizes, i.e., CdSeXL (T1), CdSeXL (T2), and CdSeXL (T3) were simulated with quantum dynamical methods, which qualitatively match the reported experimental spectra. The carbazole is attached with a 3-amino group at the apex position of T1 (namely T1-3A-Cz), establishing proper electronic communication between T1 and carbazole. The spectra of T1-3A-Cz is 0.22 eV red-shifted compared to T1. A time-dependent perturbation was applied in tune with the lowest energy peak (3.63 eV) of T1-3A-Cz to investigate the charge transfer dynamics, which revealed an ultrafast charge separation within the femtosecond time scale. The electronic structure showed a favorable energy alignment between T1 and carbazole in T1-3A-Cz. The LUMO of carbazole was situated below the conduction band of the QD, while the HOMO of carbazole mixed perfectly with the top of the valence band of the QD, developing the interfacial charge transfer states. These states promoted the photoexcited electron transfer directly from the CdSe core to carbazole. A rapid and enhanced charge separation occurred with the laser field strength increasing from 0.001 to 0.005 V/Å. However, T1 connected to the other positions of carbazole did not show charge separation effectively. The photoinduced charge transfer is negligible in the case of T2-carbazole systems due to poor electronic coupling, and it is not observed in T3-carbazole systems. So, the T1-3A-Cz model acts as a perfect donor-acceptor QD-molecule nanocomposite that can harvest photon energy efficiently. Further enhancement of charge transfer can be achieved by coupling more carbazoles to the T1 QD (e.g., T1-3A-Cz) due to the extension of hole delocalization between T1 and the carbazoles.
研究了与咔唑耦合的CdSe量子点（QD）中的光激发电荷转移动力学，以模拟用于光捕获应用的量子点-分子系统。用量子动力学方法模拟了不同尺寸的量子点（即CdSeXL（T1）、CdSeXL（T2）和CdSeXL（T3））的吸收光谱，其定性地与报道的实验光谱相匹配。咔唑在T1的顶点位置连接有一个3-氨基（即T1-3A-Cz），在T1和咔唑之间建立了适当的电子通信。与T1相比，T1-3A-Cz的光谱发生了0.22 eV的红移。对T1-3A-Cz的最低能量峰（3.63 eV）施加与时间相关的微扰，以研究电荷转移动力学，结果表明在飞秒时间尺度内存在超快电荷分离。电子结构表明T1和咔唑在T1-3A-Cz中具有良好的能量排列。咔唑的最低未占分子轨道（LUMO）位于量子点的导带下方，而咔唑的最高已占分子轨道（HOMO）与量子点价带顶部完美混合，形成了界面电荷转移态。这些状态促进了光激发电子直接从CdSe核转移到咔唑。随着激光场强从0.001 V/Å增加到0.005 V/Å，发生了快速且增强的电荷分离。然而，连接到咔唑其他位置的T1没有有效地显示出电荷分离。在T2-咔唑系统中，由于电子耦合较差，光诱导电荷转移可以忽略不计，而在T3-咔唑系统中未观察到电荷转移。因此，T1-3A-Cz模型作为一种完美的供体-受体量子点-分子纳米复合材料，可以有效地捕获光子能量。由于T1和咔唑之间空穴离域的扩展，通过将更多咔唑耦合到T1量子点（例如T1-3A-Cz），可以进一步增强电荷转移。
