Zinna Francesco

Supervisor: Prof. Lorenzo Di Bari

Title: Chiral lanthanide complexes as a source of circularly polarised light

Abstract: Lanthanides (III) are endowed with peculiar spectroscopic features. Their absorption and emission bands are narrow and the energies of their electronic transitions are largely independent of the coordination environment. f→f transitions are Laporte-forbidden and are associated with very weak absorption bands, but they can be conveniently observed in emission, once they reach an excited state by means of some energy transfer process. Usually this is made possible through a so-called antenna effect, which requires that the organic ligand absorbs high energy radiation and passes excitation onto the Ln(III). If the electronic levels of the donor (ligand) and the acceptor (lanthanide) match, the ligand-to-lanthanide energy transfer process can be very efficient.
Moreover chiral lanthanide complexes display often a degree of photoluminescence circular polarisation, exceeding the one of purely organic molecules (even oligomers or polymers) by 2 or 3 orders of magnitude. However, this peculiar property of Ln systems has not been fully exploited in technological applications.
The aim of this project is to synthesise new Ln complexes with high luminescence and highly polarised emission and to characterise them through optical (UV-Vis, fluorescence) and chiroptical (circular dichroism, circularly polarised luminescence) spectroscopies and paramagnetic NMR techniques.
We are also trying to employ these systems for special electronics applications. Recently, we proposed to employ chiral lanthanide complexes in organic LEDs to obtain electronic devices endowed with intrinsic highly circularly polarised emission. We succeeded to build a proof-of-concept device attaining the highest polarisation reported so far for any organic LED, and we demonstrated that lanthanides may play an important role in chiral optoelectronics and photonics.

Selected publications:
1) F. Zinna and L. Di Bari, “Lanthanide Circularly Polarized Luminescence: Bases and Applications”, Chirality, 2015, 27, 1–13.
2) F. Zinna, U. Giovanella, L. Di Bari, “Highly Circularly Polarized Electroluminescence from     a Chiral Europium Complex”, Adv. Mater., 2015, 27, 1791–1795.
3) F. Zinna, C. Resta, S. Abbate, E. Castiglioni, G. Longhi, P. Mineo, L. Di Bari, “Circularly polarized luminescence under near-UV excitation and structural elucidation of a Eu complex”, Chem. Commun., 2015, 51, 11903-11906.