A chiral Si(IV) complex bearing a 1,2,4-triazole-2,2'-diphenol ligand: synthesis, (chiro-)optical properties and computational investigation

Abstract

The reactivity of bis-3,5-phenol 1-phenyl-1,2,4-triazole, a non-symmetrical tridentate O^N^O proligand derived from Deferasirox, towards a Si(IV) precursor is herein studied. The reaction of the proligand (O1NO2)H2 with SiCl₄ afforded a highly stable homoleptic hexacoordinate complex, namely Si(O1NO2)2, in high yield. While the emission profile of the proligand - arising from an excited-state intramolecular proton transfer (ESIPT) mechanism - appears featureless and broad, the Si(IV) complex exhibits enhanced photoluminescence in the violet-to-deep-blue region, with a quantum yield of up to 32% in spin-coated thin films. A comprehensive study, combining photophysical methods and (time-dependent) density functional theory (TD-DFT) calculations, has rationalized the emissive behavior of this complex. Due to the non-symmetrical nature of the ligand, the homoleptic Si complex is obtained as a racemate of two Δ/Λ enantiomers that were separated by chiral chromatography and characterized by electronic circular dichroism (ECD). Subsequent TD-DFT calculations enabled the modelling of the ECD spectra and the assignment of the absolute configuration of the resolved enantiomers.