Abstract
A series of phosphonate ester supported lanthanide complexes bearing functionalities for subsequent immobilisation on semiconductor surfaces are prepared. Six phosphonate ester ligands (L1-L6) with varying aromatic residues are synthesised. Subsequent complexation with lanthanide chloride or -nitrate precursors (Ln = La, Nd, Dy, Er) affords the corresponding mono- or dimeric lanthanide model complexes [LnX3(L1-L3 or L5-L6)3]n (X = NO3, Cl; n = 1 (Nd, Dy, Er), 2 (La, Nd)) or [LnCl2Br(L4-Br)2(L4-Cl)]n (n = 1 (Nd, Dy, Er), 2 (La, Nd)) (1-32). All compounds are thoroughly characterised, and their luminescence properties are investigated in the visible and NIR spectral regions, where applicable.
Highlights
Lanthanide ions already find widespread application in lighting, sensing and display technologies, due to their outstanding photoluminescence properties.1–3Bis-phosphonic acid ester ligands have already been successfully shown to be versatile building blocks in transition metal organic frameworks (MOFs).4 In contrast to their carboxylic acid congeners, the key advantage of phosphonate esters originates from their lower vibrational frequencies resulting in reduced non-emissive excited state quenching and enhanced quantum yields.5 In case of lanthanide-based coordination polymers complexes with improved luminescence properties have been obtained.6 Our group has focussed on this topic during the last years preparing a variety of efficiently luminescent lanthanide based MOFs.7–9 different poly-fluoroaryl substituted mono-10,11 and bis-phosphanes,12 and phosphinic acids13 with enhanced rigidity have been prepared and investigated in terms of reactivity and coordination behaviour
To obtain distinct molecular lanthanide complexes with enhanced excited state lifetimes in the context of a future attachment to semiconductor surfaces, our research focusses on preparation of aryl-substituted mono phosphonate ester ligands
To obtain a ligand with increased bulkiness and antenna effect, anthracenebased L3 is prepared in a two-step synthesis starting with a modified double bromination reaction of 9-(hydroxymethyl) anthracene
Summary
Lanthanide ions already find widespread application in lighting, sensing and display technologies, due to their outstanding photoluminescence properties.1–3Bis-phosphonic acid ester ligands have already been successfully shown to be versatile building blocks in transition metal organic frameworks (MOFs).4 In contrast to their carboxylic acid congeners, the key advantage of phosphonate esters originates from their lower vibrational frequencies resulting in reduced non-emissive excited state quenching and enhanced quantum yields.5 In case of lanthanide-based coordination polymers complexes with improved luminescence properties have been obtained.6 Our group has focussed on this topic during the last years preparing a variety of efficiently luminescent lanthanide based MOFs.7–9 different poly-fluoroaryl substituted mono-10,11 and bis-phosphanes,12 and phosphinic acids13 with enhanced rigidity have been prepared and investigated in terms of reactivity and coordination behaviour. With the desired phosphonate ester ligands L1–L6 in hand, synthesis of derived lanthanide complexes (Ln = La, Nd, Dy, Er) is performed in EtOH starting from [LnX3(H2O)6] precursors (Scheme 3, vide infra).
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