Binuclear Iridium(III) Complexes for White-Emitting OLEDs

Project Information

Lefko-Phos

Grant agreement ID: 842633

DOI

10.3030/842633

Project closed

EC signature date 12 April 2019

Start date 15 February 2020

End date 14 February 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 171 473,28

EU contribution

€ 171 473,28

Coordinated by

CONSIGLIO NAZIONALE DELLE RICERCHE
Italy

Periodic Reporting for period 1 - Lefko-Phos (Binuclear Iridium(III) Complexes for White-Emitting OLEDs)

Reporting period: 2020-02-15 to 2022-02-14

Summary of the context and overall objectives of the project

The main objective of Lefko-Phoς is the development of photoactive materials emitting white light with high efficiency and high thermal, photochemical and electrochemical stability. Such materials are designed to be used in white-emitting OLEDs (WOLEDs).

Current WOLED technology (for lighting or displays) requires the use of multiple luminophores in a single device by using (i) three different red-green-blue emitters or (ii) two-colour combination of blue-orange emissive materials. However, these strategies often do not work properly, because the final materials delivered imbalanced white-light emission, low efficiency and colour instability, due to the different stability over time of each single emitter. Moreover, the manufacturing process of WOLEDs becomes more complicated due to the incorporation of multiple emissive layers or a single emissive layer with multiple dopants.

To overcome these drawbacks, Lefko-Phoς attempts to generate white-light emission from a single-component material. The target emitters are binuclear cyclometalated iridium(III) complexes, whose emitting units are linked by a non-conjugated bridging ligand.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first target of Lefko-Phoς was the creation of a library of unconjugated bridging ligands based on oxadiazole spacers. Two main types of bridges were explored: (1) a linear one with a central para-phenylene moiety and (2) a bent one with a meta substitution. The two terminal groups of the bridge were subsequently equipped with structurally different ancillary-ligand moieties capable of chelating an iridium(III) ion. Several cyclometalating ligands were also explored to tune the emission properties of the two uncoupled iridium-based centers for obtaining truly complementary emission colors.

All the synthesized complexes were structurally characterized by NMR and X-ray diffraction techniques. The electronic and optical properties of such materials were investigated by electrochemical methods and by UV-visible absorption and emission spectroscopy, using both steady-state and time-resolved techniques. All the experimental findings were properly rationalized with the help of computational modeling, using density-functional theory. The most promising emitters are currently tested as single-molecule emitting materials in white-emitting OLEDs (WOLEDs).

The outcomes of the project have been presented at two national and international conferences. At least two peer-reviewed scientific publications will be shortly submitted to prove the efficacy of the Lefko-Phoς approach for the fabrication of single-molecule WOLEDs.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Lefko-Phoς shed light on the relatively unexplored field of heteroleptic binuclear iridium(III) complexes contributing to the understanding of both the stereochemistry of these compounds and the energy-transfer processes occurring within these photoactive arrays.

The scientific knowledge produced by Lefko-Phoς will contribute to evaluate the feasibility of using white-emitting single-molecule active materials for the industrial productions of WOLEDs. This action can contribute to achieve the ambitious targets the European Union set in its amended Energy Efficiency Directive 2018/2002.

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