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

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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

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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