The Solid-State Emission of AIPE-Active Tricarbonylrhenium(I) Complexes Shifts to the Red: The Unexpected Performance of Triphenylphosphine Derivatives

Abstract

Red emitters suitable for solid-state applications are the subject of intense research. However, their development is delicate because, in general, the more the emission is red-shifted, the more its efficiency decreases. In this work, two series of phosphorescent tricarbonylrhenium complexes were synthesized and studied, both theoretically and experimentally. Their organic ligand is a phenyl-substituted quinoline or quinoxaline derivative. They also differ in their ancillary ligand, chloride or triphenylphosphine (TPP), and the presence of a bulky adamantyl substituent, initially introduced to improve the solid-state arrangement and thus the light emission efficiency. Unsurprisingly, chlorido complexes were not luminescent in solution, and only quinoline derivatives emitted faint red light in the solid state. In contrast, phosphino complexes were weakly phosphorescent in solution and showed strong solid-state luminescence enhancement. A red emission was observed for the microcrystalline powders of quinoxaline derivatives, with a PLQY up to 43%, a performance rarely achieved in this spectral region. This effect was attributed to the double intra- and intermolecular stabilization provided by the TPP moiety. The phosphino complexes were very well suited to aggregation-induced phosphorescence emission (AIPE) experiments. Their potential interest for related applications was shown. An adamantyl-substituted complex was used for the detection of sodium deoxycholate by taking advantage of the competition between these two compounds for a $\beta$-cyclodextrin. Until now, phosphino tricarbonylrhenium complexes have been mainly exploited for their photodecarbonylation properties useful in phototherapy. This work shows that they are photostable after proper chemical modifications, and that their unique spectroscopic properties make them the leaders of a new generation of red emitters.