Effects of fluorination on iridium(III) complex phosphorescence: Magnetic circular dichroism and relativistic time-dependent density functional theory

Smith, A. R. G., Riley, M. J., Burn, P. L., Gentle, I. R., Lo, S.-C. and Powell, B. J. (2012) Effects of fluorination on iridium(III) complex phosphorescence: Magnetic circular dichroism and relativistic time-dependent density functional theory. Inorganic Chemistry, 51 5: 2821-2831. doi:10.1021/ic201899z


Author Smith, A. R. G.
Riley, M. J.
Burn, P. L.
Gentle, I. R.
Lo, S.-C.
Powell, B. J.
Title Effects of fluorination on iridium(III) complex phosphorescence: Magnetic circular dichroism and relativistic time-dependent density functional theory
Journal name Inorganic Chemistry   Check publisher's open access policy
ISSN 0020-1669
1520-510X
Publication date 2012-03-05
Sub-type Article (original research)
DOI 10.1021/ic201899z
Volume 51
Issue 5
Start page 2821
End page 2831
Total pages 11
Place of publication Washington, DC, United States
Publisher American Chemical Society
Collection year 2013
Language eng
Formatted abstract
We use a combination of low temperature, high field magnetic circular dichroism, absorption, and emission spectroscopy with relativistic time-dependent density functional calculations to reveal a subtle interplay between the effects of chemical substitution and spin–orbit coupling (SOC) in a family of iridium(III) complexes. Fluorination at the ortho and para positions of the phenyl group of fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) cause changes that are independent of whether the other position is fluorinated or protonated. This is demonstrated by a simple linear relationship found for a range of measured and calculated properties of these complexes. Further, we show that the phosphorescent radiative rate, kr, is determined by the degree to which SOC is able to hybridize T1 to S3 and that kr is proportional to the inverse fourth power of the energy gap between these excitations. We show that fluorination in the para position leads to a much larger increase of the energy gap than fluorination at the ortho position. Theory is used to trace this back to the fact that fluorination at the para position increases the difference in electron density between the phenyl and triazolyl groups, which distorts the complex further from octahedral symmetry, and increases the energy separation between the highest occupied molecular orbital (HOMO) and the HOMO-1. This provides a new design criterion for phosphorescent iridium(III) complexes for organic optoelectronic applications. In contrast, the nonradiative rate is greatly enhanced by fluorination at the ortho position. This may be connected to a significant redistribution of spectral weight. We also show that the lowest energy excitation, 1A, has almost no oscillator strength; therefore, the second lowest excitation, 2E, is the dominant emissive state at room temperature. Nevertheless the mirror image rule between absorption and emission is obeyed, as 2E is responsible for both absorption and emission at all but very low (<10 K) temperatures.
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2013 Collection
School of Chemistry and Molecular Biosciences
 
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Created: Wed, 16 May 2012, 05:02:06 EST by Dr Shih-chun Lo on behalf of School of Chemistry & Molecular Biosciences