Highly Efficient Visible-to-NIR Luminescence of Lanthanide(III) Complexes with Zwitterionic Ligands Bearing Charge-Transfer Character: Beyond Triplet Sensitization

• Published in: Chemistry : a European journal Vol. 22; no. 7; pp. 2440 - 2451
• Main Authors: Pan, Mei, Du, Bin-Bin, Zhu, Yi-Xuan, Yue, Mei-Qin, Wei, Zhang-Wen, Su, Cheng-Yong
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 12.02.2016; Wiley Subscription Services, Inc
• Subjects: Charge transfer; Chemistry; Coordination compounds; Dysprosium; Energy levels; energy transfer; Excitation; Gadolinium; Lanthanides; Lanthanum; Ligands; Luminescence; Photoluminescence; Photons; Samarium; Solid solutions; Temperature dependence; Ternary systems; Tuning; White light; Zwitterions; energy transfer; zwitterions; luminescence; white light; charge transfer; lanthanides
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201504344

Two zwitterionic‐type ligands featuring π–π* and intraligand charge‐transfer (ILCT) excited states, namely 1,1′‐(2,3,5,6‐tetramethyl‐1,4‐phenylene)bis(methylene)dipyridinium‐4‐olate (TMPBPO) and 1‐dodecylpyridin‐4(1 H)‐one (DOPO), have been prepared and applied to the assembly of lanthanide coordination complexes in an effort to understand the ligand‐direction effect on the structure of the Ln complexes and the ligand sensitization effect on the luminescence of the Ln complexes. Due to the wide‐band triplet states plus additional ILCT excitation states extending into lower energy levels, broadly and strongly sensitized photoluminescence of f→f transitions from various Ln3+ ions were observed to cover the visible to near‐infrared (NIR) regions. Among which, the Pr, Sm, Dy, and Tm complexes simultaneously display both strong visible and NIR emissions. Based on the isostructural feature of the Ln complexes, color tuning and single‐component white light was achieved by preparation of solid solutions of the ternary systems Gd‐Eu‐Tb (for TMPBPO) and La‐Eu‐Tb and La‐Dy‐Sm (for DOPO). Moreover, the visible and NIR luminescence lifetimes of the Ln complexes with the TMPBPO ligand were investigated from 77 to 298 K, revealing a strong temperature dependence of the Tm3+ (3H4) and Yb3+ (2F5/2) decay dynamics, which has not been explored before for their coordination complexes. Little light: Two new types of zwitterionic ligands have been designed that show broad sensitization from both triplet and ILCT states for the whole series of LnIII ions in both the visible and the NIR region (see figure), as well as single‐phase white‐light emission.