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Molecular design of novel luminescent complexes based on hybrid phosphine ligands for chemo- and biosensing applications

Subject Area Inorganic Molecular Chemistry - Synthesis and Characterisation
Term from 2019 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 405832919
 
Final Report Year 2024

Final Report Abstract

Luminescent metal complexes have attracted increasing attention over the last few decades for widespread applications, such as in photochemistry, organic optoelectronics, and in the development of luminescent sensors. In contrast to organic fluorophores, which are singlet emitters, transition metal complexes display triplet emission due to spin–orbit coupling, which leads to efficient singlet–triplet state mixing and enhancement of phosphorescence. The properties of the excited states depend on the metal centre and the ligands, and thus, the photophysical properties (such as emission wavelength, lifetime, and intensity) can be modified for specific applications. This joint project aimed to provide access to novel luminescent systems based on the class of multidonor hybrid phosphorus-containing heterocycles, namely cyclic aminomethylphosphines, and their transition metal complexes with AuI, CuI, and PtII for applications in biosensing and bioimaging. Cyclic aminomethylphosphines are of interest because they are not only structure-forming ligands, but can also be functionalised easily with luminescent and sensing moieties with retention of the coordinating framework. A library of 1,5-diaza-3,7-diphosphacyclooctane ligands with different physical and stereoelectronic properties has been synthesised by condensation reaction of primary heteroaryl phosphines with formaldehyde and subsequent ring formation through addition of primary amines. Chromophoric heteroaromatic substituents at phosphorus and nitrogen provide luminescence properties and additional binding sites for heterometallic assemblies. A wide range of mono- and dinuclear complexes of copper(I), gold(I) and platinum(II) with 1,5- diaza-3,7-diphosphacyclooctane ligands containing heteroaryl substituents at phosphorus and aryl or alkylaryl substituents at nitrogen were obtained and fully characterised in solution and the solid state. Cationic complexes of copper(I) and dinuclear complexes of gold(I) proved to be the most promising candidates in terms of creating sensors capable of responding to external factors. Especially the gold(I) complexes can form colloidal nanoparticles, which makes them attractive for biological applications. The gold(I) complex with 1,5-bis(p-tolyl)-3,7-bis(pyridin-2-yl)-1,5-diaza-3,7-diphosphacyclooctane as ligand ([AuCl)2L]) forms core-shell type nanoparticles with polyethyleneimine (PEI) in aqueous solution which could be employed for cell staining (bioimaging).

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