联三吡啶铂(Ⅱ)配合物的非线性吸收和光限幅（特邀）

本文总结了2003~2019年报道的联三吡啶铂（Ⅱ）配合物的反饱和吸收或双光子吸收及光限幅研究进展，并对这类配合物的光物理特性，包括基态吸收?激发态吸收?激发态寿命和三重态量子产率?在532 nm的反饱和吸收或光限幅，在近红外光区的双光子吸收，以及构效关系进行了评估。首先介绍了目前光限幅材料和器件的研究现状，对反饱和吸收和双光子吸收材料的基本要求，以及平面正方形铂（Ⅱ）配合物的种类和特性；其次讨论了六个系列联三吡啶类铂（Ⅱ）配合物的反饱和吸收或光限幅及构效关系；随后总结了五个系列联三吡啶铂（Ⅱ）配合物的双光子吸收及结构变化对双光子吸收截面的影响；最后对文献报道的工作进行了小结。根据文献报道的工作发现的一个趋势是:在联三吡啶配体或单齿炔配体上引入取代基可以调节基态和激发态的吸收，特别是在配体上引入给电子基团或增加联三吡啶和其上的芳香环取代基的共平面性会引起基态吸收红移但降低或淬灭激发态的吸收，这样会降低在532 nm的反饱和吸收或光限幅。但是扩展联三吡啶配体上的共轭体系则能大幅提高铂（Ⅱ）配合物的双光子吸收截面，尤其是在联三吡啶配体上引入吸电子的共轭芳香环取代基可以控制基态吸收在500 nm以下，同时保持了在可见光区的长寿命宽幅三重激发态吸收和在近红外光区的中等强度的双光子吸收，这对研制宽幅激光限幅材料有重要意义。

Nonlinear absorption and optical limiting of platinum(Ⅱ) terpyridine complexes (Invited)

The reported work in 2003-2019 on the reverse saturable absorption (RSA) or two-photon absorption (TPA) and/or optical limiting (OPL) of platinum(II) terpyridine complexes was summarized in this minireview. Photophysical properties, including the ground-state absorption (GSA), excited-state absorption (ESA), excited-state lifetimes, and the quantum yields of triplet excited-state formation, RSA/OPL at 532 nm for ns laser pulses, TPA characteristics in the near-IR spectral regions, and the structure-property correlations were reviewed. This paper is composed of four sections. First, the current status of OPL materials and devices, the general requirements for reverse saturable absorbers and two-photon absorbing materials, and the different types and characteristics of square-planar platinum(II) complexes were briefly introduced. Then the photophysics and RSA/OPL of six series of Pt(Ⅱ) terpyridine-analogous complexes and the structure-property correlations were discussed. Following it the TPA of five series of Pt(Ⅱ) terpyridine complexes and the impacts of structural variations on the TPA cross sections (σ₂) were reviewed. Finally, brief conclusions were drawn based on the reported studies. A general trend discovered was that the charge transfer absorption band(s) and the ESA can be readily tuned by substituents on the acetylide or the terpyridine ligand. Introducing electron-donating substituent to the acetylide or terpyridine ligand or improving the coplanarity between the aromatic substituent and the terpyridine ligand red-shifted the ground-state charge-transfer absorption band(s) at the price of decreasing/quenching the triplet ESA, which consequently reduced the RSA/OPL at 532 nm. Extending the π-conjugation of the terpyridine ligand dramatically improved the σ₂ values of the Pt(Ⅱ) terpyridine complexes. Incorporation of electron-withdrawing π-conjugated aromatic substituent restrained the GSA to < 500 nm while keeping a long-lived triplet excited state with broadband ESA in the visible spectral regions and moderately strong TPA in the NIR regions. This approach could provide a solution for developing broadband OPL materials.