Temperature dependent NIR emitting lanthanide-PMO/silica hybrid materials

Abstract

Two materials – a mesoporous silica (MS) and a periodic mesoporous organosilica (PMO) functionalized with dipyridyl-pyridazine (dppz) units were grafted with near-infrared (NIR) emitting lanthanide (Nd³⁺, Er³⁺, Yb³⁺) complexes in an attempt to obtain hybrid NIR emitting materials. The parent materials: dppz-vSilica and dppz-ePMO were prepared by a hetero Diels–Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) and the double bonds of either ethenylene-bridged PMO (ePMO) or vinyl-silica (vSilica) and subsequent oxidation. The dppz-vSilica is reported here for the first time. The prepared lanthanide-PMO/silica hybrid materials were studied in depth for their luminescence properties at room temperature and chosen Nd³⁺ and Yb³⁺ samples also at low temperature (as low as 10 K). We show that both the dppz-vSilica and dppz-ePMO materials can be used as “platforms” for obtaining porous materials showing NIR luminescence. To obtain NIR emission these materials can be excited either in the UV or Vis region (into the π → π* transitions of the ligands or directly into the f–f transitions of the Ln³⁺ ions). More interestingly, when functionalized with Nd³⁺ or Yb³⁺ β-diketonate complexes these materials showed interesting luminescence properties over a wide temperature range (10–360 K). The Yb³⁺ materials were investigated for their potential use as ratiometric temperature sensors.