Chen Zhihui, Xu Defeng, Zhu Menglong, Wang Yueting, Feng Junfan, Shu Chuancun, Xiao Si, Meng Jianqiao, He Jun
Hunan Key Laboratory of Nanophotonics and Devices, School of Physics and Electronics, Central South University, Changsha 410083, China.
Department of Applied Physics, School of Microelectronics and Physics, Hunan University of Technology and Business, Changsha 410205, China.
Nanophotonics. 2023 Sep 12;12(19):3781-3791. doi: 10.1515/nanoph-2023-0383. eCollection 2023 Sep.
As an important means of modern science and technology, multiphoton fluorescence plays an essential role in high-resolution imaging, photochemistry, micro- and nano-processing and clinical diagnosis. Multiphoton fluorescence usually shares the same radiative channel as its intrinsic fluorescence. Under multiphoton excitation, except for red shift fluorescence caused by the reabsorption effect, gigantic blue shift of multiphoton fluorescence is rarely reported. In this work, metal-organic frameworks (MOFs) with 7-fold and 8-fold interpenetration are successfully synthesized. The synthesized 8-fold interpenetrated MOFs show unexpectedly giant blue-shifted (∼40 nm) two-photon-induced fluorescence compared with its fluorescence emission. Specific optical selection rules lead to different final transition states in one-photon absorption and two-photon absorption. The density functional theory (DFT) and time-dependent density functional theory (TDDFT) simulations show that, under two-photon excitation, electrons and holes can be more delocalized, and intermolecular interactions mainly govern the emission process of 8-fold interpenetrated MOFs. Highly excited electronic states of the interpenetrated MOFs are effectively excited and emitted under two-photon excitation, thus generating the inevitable blue-shifted two-photon-induced fluorescence emission. Our work provides a guide for exploring the excitation mechanism of fluorescent MOFs and offers an access to a tunable all-optical single-crystal device.
作为现代科学技术的一种重要手段，多光子荧光在高分辨率成像、光化学、微纳加工及临床诊断中发挥着至关重要的作用。多光子荧光通常与其本征荧光共享相同的辐射通道。在多光子激发下，除了由再吸收效应引起的红移荧光外，多光子荧光的巨大蓝移鲜有报道。在这项工作中，成功合成了具有七重和八重穿插结构的金属有机框架（MOF）。与荧光发射相比，合成的八重穿插MOF表现出意想不到的巨大蓝移（约40纳米）双光子诱导荧光。特定的光学选择规则导致单光子吸收和双光子吸收中的最终跃迁态不同。密度泛函理论（DFT）和含时密度泛函理论（TDDFT）模拟表明，在双光子激发下，电子和空穴能够更离域，分子间相互作用主要支配八重穿插MOF的发射过程。在双光子激发下，穿插MOF的高激发电子态被有效激发并发射，从而产生不可避免的蓝移双光子诱导荧光发射。我们的工作为探索荧光MOF的激发机制提供了指导，并为可调谐全光单晶器件提供了途径。
