Two-photon absorption (TPA) materials have wide range of applications in the upconversion luminescent material, bioimaging, photodynamic therapy, three-dimensional lithographic microfabrication, etc. By using metal centers as template, metal complexes can combine several TPA active organic ligands into a complicate multipolar system to achieve enhanced TPA effect. The resulting two-photon absorptive material also displays better stability, extended emission lifetime and optimized spectral range when compared with the pure ligands. The "cooperative enhancement" effect in the TPA cross-section of multinuclear metal complex has drawn broad attention. In this paper, representative multinuclear complexes(homonuclear and heteronuclear) are selected to study the influencing factors on their TPA properties, such as the type and amount of metal ions, the structure of ligand molecules and complexes, etc. Special attention is paid to the mechanism of their photophysical properties that explain the structure and energy level of the excited states, the mode and direction of energy transfer in the multinuclear complexes, hoping to summarize the molecular design rules for TPA active multinuclear complexes. Finally, the existing problems in the research of multinuclear complexes with two-photon activity are described and studies on the "bifunctional multinuclear" complex are prospected, which will provide an important base for future development of novel two-photon absorptive materials.
Contents
1 Introduction
2 Homometallic multinuclear complexes
2.1 Multinuclear platinum complex
2.2 Multinuclear ruthenium complexes
2.3 Multinuclear zinc complexes
2.4 Multinuclear iridium complexes
2.5 Multinuclear iron complexes
2.6 Copper clusters
2.7 Gold clusters
2.8 Other metal complexes
3 Heterometallic multinuclear complexes
3.1 d-f type heteronuclear complex
3.2 d-d type heteronuclear complex
3.3 Clusters and MOF Structures
3.4 Biological applications of heterometallic complexes
4 Conclusion and outlook