Invited for this month′s cover are the collaborating groups of Yuichi Kitagawa, Yasuchika Hasegawa, Tetsuya Taketsugu, and co‐workers at Hokkaido University. The cover picture shows a photosensitizer that has a long excited‐state lifetime and provides strong emissions for TbIII coordination polymers. The photosensitization ability can be considerably altered by changing the ancillary ligands in the TbIII coordination polymers. The results provide new insights on the design of photosensitizers for improving the properties of photo‐functional materials. More information can be found in the Research Article by Y. Kitagawa, Y. Hasegawa, and co‐workers.

Molecular photosensitizers provide efficient light-absorbing abilities for photo-functional materials. Herein, effective photosensitization in excited-state equilibrium is demonstrated using five Tb III coordination polymers. The coordination polymers are composed of Tb III ions (emission center), hexafluoroacetylacetonato (photosensitizer ligands), and phosphine oxide-based bridges (ancillary ligands). The two types of ligand combinations induces a rigid coordination structure via intermolecular interactions, resulting in high thermal stability (with decom-position temperatures above 300 °C). Excited-triplet-state lifetimes of photosensitizer ligands (τ = 120-1320 μs) are strongly dependent on the structure of the ancillary ligands. The photosensitizer with a long excited-triplet-state lifetime (τ � 1120 μs) controls the excited state equilibrium between the photosensitizer and Tb III , allowing the construction of Tb III coordination polymer with high Tb III emission quantum yield (� 70 %).

In this study, we have demonstrated a two-legged, upright molecular design method for monochromatic and bright red luminescent Ln III -silica nanomaterials. A novel Eu IIIsilica hybrid nanoparticle was developed by using a doubly binding TPPOÀ Si(OEt) 3 (TPPO: triphenyl phosphine oxide) linker. The TPPOÀ Si(OEt) 3 was confirmed by 1 H, 31 P, 29 Si NMR spectroscopy and single-crystal X-ray analysis. Luminescent Eu(hfa) 3 and Eu(tfc) 3 moieties (hfa: hexafluoroacetylacetonate, tfc: 3-(trifluoromethylhydroxymethylene)camphorate) were fixed onto TPPOÀ Si(OEt) 3 -modified silica nanoparticles, producing Eu(hfa) 3 (TPPOÀ Si) 2 -SiO 2 and Eu(tfc) 3 (TPPOÀ Si) 2 -SiO 2 , respectively. Eu(hfa) 3 (TPPOÀ Si) 2 À SiO 2 exhibited the higher intrinsic luminescence quantum yield (93 %) and longer emission lifetime (0.98 ms), which is much larger than those of previously reported Eu III -based hybrid materials. Eu-(tfc) 3 (TPPOÀ Si) 2 À SiO 2 showed an extra-large intrinsic emission quantum yield (54 %), although the emission quantum yield for the precursor Eu(tfc) 3 (TPPOÀ Si(OEt) 3 ) 2 was found to be 39 %. These results confirmed that the TPPOÀ Si(OEt) 3 linker is a promising candidate for development of Eu III -based luminescent materials.

A two‐legged, standing‐up molecular design method for monochromatic and bright red luminescent EuIII–silica nanomaterials is demonstrated. By using a Eu(hfa)3 complex with TPPO‐Si(OEt)3 (hfa: hexafluoroacetylacetonate, TPPO: triphenyl phosphine oxide) covalently bonded to the silica nanoparticles at two binding sites, nanoluminophores Eu(hfa)3(TPPO‐Si)2–SiO2 were developed that have an excellent intrinsic luminescence quantum yield (93%) and long emission lifetime (0.98 ms). More information can be found in the Full Paper by Y. Hasegawa et al. (DOI: 10.1002/chem.202102156).

The cover picture shows a photosensitizer that has a long excited‐state lifetime and provides strong emissions for TbIII coordination polymers. The coordination polymers are composed of TbIII ions (emission center), hexafluoroacetylacetonato (photosensitizer ligands), and phosphine oxide‐based bridges (ancillary ligands). The photosensitizer with a long excited‐triplet‐state lifetime (τ≥1120 μs) controls the excited state equilibrium between the photosensitizer and TbIII, allowing the construction of TbIII coordination polymer with high TbIII emission quantum yield. More information can be found in the Research Article by Y. Kitagawa, Y. Hasegawa, and co‐workers.