Issue 13, 2016

The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(iii) cyclometalates

Abstract

A family of heteroleptic iridium(III) cyclometalates, [4-(2-RCB)ppy]2Ir(acac) (3c–3g; CB = o-carboran-1-yl; ppy = 2-phenylpyridinato-C2,N; acac = acetylacetonate; R = iPr (3c), iBu (3d), Ph (3e), CF3C6H4 (3f), C6F5 (3g)) with various 2-R substituted o-carboranes at the 4-position in the phenyl ring of the ppy ligand, were prepared. The X-ray crystal structure of all complexes, including 3a (R = H) and 3b (R = Me), showed that while the carboranyl C–C bond distance increases with the increasing steric effect of the 2-R substituent (3a–3d), the bond distance is more likely to be influenced by the electronic effect of the substituent for the 2-aryl substituted complexes (3e–3g). The absorption and emission bands of all complexes were red-shifted with respect to those of the parent (ppy)2Ir(acac) (4). While 3a–3d exhibited intense green phosphorescence with good quantum efficiency in toluene (ΦPL = 0.17–0.47), the complexes were poorly emissive in THF (ΦPL < 0.004). In a PMMA film, however, 3a–3d became substantially emissive (ΦPL = 0.11–0.14, 8 wt% Ir), albeit less emissive than 4 (ΦPL = 0.15). In contrast, the 2-aryl substituted 3e–3g were almost non-emissive in both the solution and solid states. All complexes underwent facile carborane-centered, electrochemical reduction (Eonset = −2.01 to −1.22 V). The potential values of these reductions increased with increases in the electron accepting ability of the 2-R group (H < alkyl < aryl) and were largely shifted anodically with respect to those of 4 and 5-carborane substituted complexes. This reduction behavior of 3a–3g implies that the LUMO contribution of 2-R-o-carborane units increases through the substitution at the 4-position of the ppy ligand and is influenced by the nature of the 2-R group, which may be responsible for facile carboranyl C–C bond variation leading to efficient quenching of the emissive excited states.

Graphical abstract: The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(iii) cyclometalates

Supplementary files

Article information

Article type
Paper
Submitted
06 Jan 2016
Accepted
17 Feb 2016
First published
17 Feb 2016

Dalton Trans., 2016,45, 5667-5675

The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(III) cyclometalates

J. Park, Y. H. Lee, J. Y. Ryu, J. Lee and M. H. Lee, Dalton Trans., 2016, 45, 5667 DOI: 10.1039/C6DT00065G

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements