Aggregation induces circularly polarized light emission in platinum complexes

A team of researchers, including ICReDD Associate Professor Yuuya Nagata and led by Professor Hiroyuki Nishikawa at Ibaraki University, have reported the development of a chiral platinum(II) complex that displays circularly polarized phosphorescence. Such circularly polarized light emission is potentially valuable for advanced technological applications, including visual displays, chemical and bio-sensing, and optical information communication.

The complexes were constructed by attaching two commercially available ligand molecules to platinum atoms. These complexes formed a helical stacking structure through interactions between the ligands. While no light emission was observed in the solution, red light emission was seen for the platinum complexes in powder form, and white light emission was observed when the complexes were dispersed as a thin film in the polymer material, poly(methylmethacrylate) (PMMA). This result indicates the emission is aggregation induced. Analysis of the photoluminescence of the samples suggests the white light emission is due to the presence of both the monomer and aggregate forms of the platinum complexes co-existing in the PMMA. As the percentage of the platinum complex dispersed in PMMA was increased, the emission color was found to be changed from white to red (1 wt%: white, 2 wt%: yellow, 5 wt%: red).

White light OLEDs are generally made from a combination of emitting molecules. However, the complex developed here could contribute to the development of single-molecule white OLEDs with circularly polarized emission.

The structure of chiral platinum complexes developed in this study (center) and the complex in powder form (left) and as a thin film in PMMA (right).