Issue 15, 2021

Tuning the optical bandgap and piezoresistance in iridium-based molecular semiconductors through ligand modification

Abstract

Square-planar d8 metal complexes are known to stack with short metal–metal distances in the solid-state, forming linear molecular chains with conductive pathways that can be enhanced under pressure. Although the influence of the metallic centre on the behaviour of these materials has been previously studied, the role and significance of ligand choice has received less focus. Here, we study the relationship between the structural, optical and conductive properties of a series of d8 iridium dicarbonyl complexes with different β-diketonate ligands using a combination of experimental and computational methods. Our results show that ligand choice contributes significantly to the optical transitions of the molecules in solution by lowering the LUMO energy for complexes with π-conjugation or electronegative atoms. We also show that ligand choice is a pathway for band-structure tuning in the molecular crystal through ligand size selection and associated structural packing, with complexes packing in linear metal–metal stacks exhibiting a smaller optical bandgap in the solid state. With pressure-dependent measurements, we confirm that that favourable metal–metal stacking in the solid obtained by appropriate ligand choice leads to higher conductivity at lower pressures. Our results provide insight for the design and application of d8 metal complexes in optoelectronic devices and the development of future molecular materials.

Graphical abstract: Tuning the optical bandgap and piezoresistance in iridium-based molecular semiconductors through ligand modification

Supplementary files

Article information

Article type
Paper
Submitted
06 May 2021
Accepted
25 Jun 2021
First published
29 Jun 2021
This article is Open Access
Creative Commons BY license

Mater. Adv., 2021,2, 5135-5143

Tuning the optical bandgap and piezoresistance in iridium-based molecular semiconductors through ligand modification

S. Eizagirre Barker, H. Benjamin, C. A. Morrison, S. Afanasjevs, G. S. Nichol, S. Moggach, K. Kamenev and N. Robertson, Mater. Adv., 2021, 2, 5135 DOI: 10.1039/D1MA00416F

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