Chiral luminescent lanthanide complexes: bridging technological and biological frontiers

The increasing applications of trivalent lanthanide complexes can be attributed to the distinctive characteristics of f-f transitions. These include extended emission excited state lifetimes, well-defined and easily distinguishable emission bands, and a significant shift between absorbed and emitted radiation. Circularly Polarized Luminescence (CPL) is a chiroptical phenomenon which is gaining increasing interest thanks to the broad range of possible technological and biological applications. In this scenario, as the emission of CP light by trivalent lanthanide ions is an efficient phenomenon, luminescent lanthanide complexes play a pivotal role. From a technological perspective, these elements could logically be applied in displays, where polarised light prevents ambient light reflection, leading to high-contrast 3D images and true black. From a biological standpoint, as for the lanthanide complexes exhibiting two-photon (2P) excitation, advancing 2P-CPL microscopy experiments can be exploited for fundamental investigations into chiral interactions within chemistry and molecular biology. The objectives of this PhD project have been the synthesis and characterisation of chiral enantiomeric complexes of Ln(III) containing the chiral fragment 1,2-trans-diaminecyclohexane (DACH) for technological applications [Ln=Eu(III) and Tb(III)] and for biological applications [Ln=Sm(III), Eu(III), Yb(III) and Nd(III)]. With this aim, as for the design of Ln(III)-based luminescent complexes, it is important to take into account several requirements, such as high thermodynamic stability and kinetic inertness. Furthermore, apart from a suitable chromophoric ligand (antenna) capable of protecting the lanthanide ion from the intrusion of solvent (water) molecules and sensitising its luminescence, one additional important feature of the ligand is to ensure a suitable excitation wavelength to the system. This particularly applies when the complex is designed for biological applications. Often, to excite the antenna, UV light is used, but in the biological field this represents a drawback, since this radiation is hazardous for cells and possesses a small penetration depth in tissues. An elegant solution to overcome this problem is the use of near-infrared light as excitation source. To summarize, this thesis is focused on two primary aspects: i) the development of innovative heteroleptic complexes combining β-diketonates derivatives and chiral ligands to generate optical materials able to efficiently emit CPL and ii) the exploration of novel bioprobes with an excitation wavelength extended to the Visible-NIR spectral windows.