Neutral RuII-based emitting materials: A prototypical study on factors governing radiationless transition in phosphorescent metal complexes

Elise Y. Li, Yi Ming Cheng, Cheng Chih Hsu, Pi Tai Chou*, Gene Hsiang Lee, I. Hui Lin, Yun Chi, Chao Shiuan Liu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

48 Citations (Scopus)

Abstract

In addition to the metal-centered dd transition that is widely accepted as a dominant radiationless decay channel, other factors may also play important roles in governing the loss of phosphorescence efficiency for heavy-transition-metal complexes. To conduct our investigation, we synthesized two dicarbonylruthenium complexes with formulas [Ru(CO)2(BQ) 2] (1) and [Ru(CO)2(DBQ)2] (2), for which the cyclometalated ligands BQ and DBQ denote benzo-[h]quinoline and dibenzo[f,h]quinoxaline, respectively. Replacing one CO ligand with a P donor ligand such as PPh2Me and PPhMe2 caused one cyclometalated ligand to undergo a 180° rotation around the central metal atom, giving highly luminous metal complexes [Ru(CO)L(BQ)2] and [Ru(CO)L(DBQ) 2], where L = PPh2Me and PPhMe2 (3-6), with emission peaks λmax in the range of 571-656 nm measured in the fluid state at room temperature. It is notable that the S0-T 1 energy gap for both 1 and 2 is much higher than that of 3-6, but the corresponding phosphorescent spectral intensity is much weaker. Using these cyclometalated Ru metal complexes as a prototype, our experimental results and theoretical analysis draw attention to the fact that, for complexes 1 and 2, the weaker spin-orbit coupling present within these molecules reduces the T 1-S0 interaction, from which the thermally activated radiationless deactivation may take place. This, in combination with the much smaller 3MLCT contribution than that observed in 3-6, rationalizes the lack of room-temperature emission for complexes 1 and 2.

Original languageEnglish
Pages (from-to)8041-8051
Number of pages11
JournalInorganic Chemistry
Volume45
Issue number20
DOIs
Publication statusPublished - 2006 Oct 2
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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