Abstract
The design of near-IR materials is highly relevant to energy and pharmaceutical sciences due to the high proportion of near-IR irradiation in the solar spectrum and the high penetration of near-IR light in biological samples. Here, we show the one-step synthesis of hexacoordinated ruthenium and iron complexes that exhibit a main absorption band in the near-IR region. For that purpose, novel tridentate ligands were prepared by condensation of two diimines and four cyanoaryl derivatives in the presence of ruthenium and iron template ions. This method was applied to a wide variety of cyanoaryl, diimine, and metal ion combinations. The relationship between the structure and the optical and electrochemical properties in the resulting complexes was examined, and the results demonstrated that these compounds represent novel near-IR materials whose physical properties can be controlled based on rational design guidelines. The intense absorption bands in the 700–900 nm region were assigned to metal-to-ligand charge transfer (MLCT) transitions, which should allow applications in materials with triplet excited states under irradiation with near-IR light.
Highlights
Light-harvesting materials play a prominent role in various fields of materials sciences, such as solar energy conversion[1,2], artificial photosynthesis[3,4], environmental analysis[5], and therapeutics[6,7]
Phthalocyanine (Pc)-metal complexes present highly symmetrical D4h structures with an intense absorption band in the visible region, whose properties can be tuned by modifications on the Pc skeleton[26]
Pc ruthenium complexes (RuPc) bearing one or two axial ligands were synthesized by a direct condensation or by ligand-substitution reactions using suitable Pc precursors[35]
Summary
Light-harvesting materials play a prominent role in various fields of materials sciences, such as solar energy conversion[1,2], artificial photosynthesis[3,4], environmental analysis[5], and therapeutics[6,7]. Near-IR light (especially the 700–1000 nm region) is “invisible” and its practical applications have remained undeveloped. Phthalocyanine (Pc)-metal complexes present highly symmetrical D4h structures with an intense absorption band in the visible region (the so-called Q band), whose properties can be tuned by modifications on the Pc skeleton[26]. Metal-to-ligand charge transfer (MLCT) transitions in the lower energy region are often essential for the unique optical properties of such Ru(II) complexes. A number of Ru(II) complexes have been designed to reduce the energy of MLCT transitions, which is commensurate with a bathochromic shift of the absorption[8,30,31,32], a general strategy toward compounds able to exploit the near-IR light (>700 nm) with high efficiency (ε > 104 M−1 cm−1) remains elusive. Regardless, the design of unusual reactions and compounds by synthetic chemistry experts remains an important topic in synthetic organic chemistry
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