Jia Jidong, Li Jie, Zhang Tianwei, Lu YinLin, Song Yinglin
School of Electronic Information, Huzhou College, Huzhou, 313000, China.
Department of Physics, Soochow University, Suzhou, 215123, China.
Phys Chem Chem Phys. 2024 Apr 3;26(14):11064-11072. doi: 10.1039/d3cp06059d.
Intramolecular charge transfer (ICT) and π-electron delocalization are two key factors affecting the nonlinear optical absorption of organic molecules. To clarify the different influences of ICT and π-electron delocalization on two-photon absorption (TPA) and excited-state absorption (ESA), monomeric coumarin C1 and dimeric coumarin C2 are synthesized and studied. Transient absorption spectroscopy (TAS) analysis of these coumarin derivatives in solvents of varying polarities describes the polarity-dependent excited-state dynamics and reveals the ESA signals of the charge transfer state (CTS) and local excited state (LES) with different spectral features. Femtosecond broadband Z-scan experiments indicate that dimeric coumarin C2 has a more significant TPA response than monomeric coumarin C1 in the near-infrared region. Natural transition orbital (NTO) analysis further theoretically characterizes the electron transition feature induced by TPA. Our results reveal that the TPA of these coumarin derivatives can be significantly enhanced by expanding π-electron delocalization, but their ESA is mainly dominated by ICT performance. This study indicates that coumarin derivatives will exhibit extremely broad application prospects in the field of ultrafast optical limiting (OL) through reasonable molecular design.
分子内电荷转移（ICT）和π电子离域是影响有机分子非线性光学吸收的两个关键因素。为了阐明ICT和π电子离域对双光子吸收（TPA）和激发态吸收（ESA）的不同影响，合成并研究了单体香豆素C1和二聚体香豆素C2。对这些香豆素衍生物在不同极性溶剂中的瞬态吸收光谱（TAS）分析描述了极性依赖的激发态动力学，并揭示了具有不同光谱特征的电荷转移态（CTS）和局域激发态（LES）的ESA信号。飞秒宽带Z扫描实验表明，在近红外区域，二聚体香豆素C2比单体香豆素C1具有更显著的TPA响应。自然跃迁轨道（NTO）分析进一步从理论上表征了TPA诱导的电子跃迁特征。我们的结果表明，通过扩展π电子离域可以显著增强这些香豆素衍生物的TPA，但它们的ESA主要由ICT性能主导。这项研究表明，通过合理的分子设计，香豆素衍生物在超快光学限幅（OL）领域将展现出极其广阔的应用前景。
