AUTHOR=Ohmagari Hitomi , Marets Nicolas , Kamata Jun , Yoneyama Mayo , Miyauchi Takumi , Takahashi Yuta , Yamamoto Yukina , Ogihara Yuto , Saito Daisuke , Goto Kenta , Ishii Ayumi , Kato Masako , Hasegawa Miki 

TITLE=Thermosensitive visible-light-excited visible-/NIR-luminescent complexes with lanthanide sensitized by the π-electronic system through intramolecular H-bonding

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.1047960

DOI=10.3389/fchem.2022.1047960

ISSN=2296-2646

ABSTRACT=Visible luminescent lanthanide complexes (LnL) with a highly planar tetradentate ligand were successfully developed for a visible-light solid-state excitation system. L was designed by using two 2-hydroxy-3-(2-pyridinyl)-benzaldehyde molecules bridged by ethylenediamine, which was then coordinated to a series of Ln ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy and Yb). From the measurement of single-crystal X-ray analysis of EuL, two phenolic O atoms and two imine N atoms in L were coordinated to the Eu ion and each π-electronic system took coplanar with the edged-pyridine moiety through an intramolecular hydrogen bond. The enol group on phenolic skeleton changed to keto form, and the pyridine was protonated. Thus, intramolecular-proton-transfer occurred in L after the complexation. Other complexes take isostructure. The space group is P-1 and the c-axis shrinks with decreasing temperature without a phase transition in EuL. The yellow color caused by the planar structure of L can sensitize ff emission by visible light, and the luminescence color of each complex depends on central Ln ions. Furthermore, a phosphorescence band also appeared at rt with ff emission in LnL. Drastic temperature dependence of luminescence was clarified quantitively.