Thermal equilibration between excited states or solvent effects: unveiling the origins of anomalous emissions in heteroleptic Ru(II) complexes

TL;DR

This study uses computational methods to analyze the temperature-dependent photoluminescence of heteroleptic Ru(II) complexes, revealing thermal equilibration as the cause of anomalous dual emissions, which is crucial for optoelectronic applications.

Contribution

It provides a computational explanation for the origin of anomalous emissions in Ru(II) complexes, emphasizing the role of thermal equilibration over solvent effects.

Findings

Thermal equilibration explains dual emission behavior.

Computational results favor temperature-driven state population changes.

Highlights importance of temperature control in optoelectronic devices.

Abstract

In this manuscript we present a computational study on the photoluminescence properties of several heteroleptic [Ru(H)(CO)(N^N)(tpp)2]+ complexes (tpp = triphenylphosphine). A special focus is set on disentangling the temperature-dependent emissive properties. Experimentally, when cooling a solution of [Ru(H)(CO)(dmphen)(tpp)2]+ (dmphen = 5,6-dimethyl-1,10-phenanthroline) from room to cryogenic temperature, a partial emission switch from metal-to-ligand charge transfer (3MLCT) to ligand-centered (3LC) phosphorescence is observed, resulting in dual photoluminescence. Two different origins of the anomalous emissions are possible, i.e., thermal equilibration between electronically excited states or different excited state solvent relaxation effects. Our calculations are in favor of the thermally equilibrated scenario. This computational investigation highlights the importance of controlling the temperature-dependent emissive behavior for optoelectronic applications.