Design Rule Hidden from The Eye in S/N‐Bridged Ancillary Ligands for Copper(I) Complexes Applied to Light‐Emitting Electrochemical Cells

• Published in: Advanced functional materials 2023-12, Vol.33 (50), p.n/a
• Main Authors: Giobbio, Ginevra, Cavinato, Luca M., Fresta, Elisa, Montrieul, Anaïs, Umuhire Mahoro, Gilbert, Lohier, Jean‐François, Renaud, Jean‐Luc, Linares, Mathieu, Gaillard, Sylvain, Costa, Rubén D.
• Format: Article
• Language: English
• Subjects: Coordination compounds; Copper; copper (I) complexes; Electrochemical cells; Electrochemical impedance spectroscopy; Ligands; light‐emitting electrochemical cells; Materials science; multivariate analysis; Multivariate statistical analysis; Performance enhancement; Photoluminescence; Quinoline; Statistical analysis; thermally activated delayed fluorescence; thin‐film lighting; Transition metal compounds
• ISSN: 1616-301X; 1616-3028; 1616-3028
• DOI: 10.1002/adfm.202304668

Enhancing low‐energy emitting Cu(I)‐ionic transition metal complexes (iTMCs) light‐emitting electrochemical cells (LECs) is of utmost importance towards Cu(I)‐iTMC‐based white‐emitting LECs. Here, the ancillary ligand design includes (i) extension of π‐systems and (ii) insertion of S‐bridge between heteroaromatics rings. This led to two novel heteroleptic Cu(I)‐iTMCs: 2‐(pyridin‐2‐yl‐l2‐azanyl)quinoline (CuN2) and 2‐(naphthalen‐2‐ylthio)quinoline (CuS2) as N^N and bis[(2‐diphenylphosphino)phenyl] ether as P^P, exhibiting improved photoluminescence quantum yields (ϕ) and thermally activated delayed fluorescence processes compared to their reference Cu(I)‐iTMCs: di(pyridin‐2‐yl)‐l2‐azane (CuN1) and di(pyridin‐2‐yl)sulfane (CuS1). Despite CuS2 stands out with the highest ϕ (38% vs 17 / 14 / 1% for CuN1 / CuN2 / CuS1), only CuN2‐LECs show the expected enhanced performance (0.35 cd A−1 at luminance of 117 cd m−2) compared to CuN1‐LECs (0.02 cd A−1 at6 cd m−2), while CuS2‐LECs feature low performances (0.04 cd A−1 at 10 cd m−2). This suggests that conventional chemical design rules are not effective towards enhancing device performance. Herein, nonconventional multivariate statistical analysis and electrochemical impedance spectroscopy studies allow to rationalize the mismatch between chemical design and device performance bringing to light a hidden design rule: polarizability of the ancillary ligand is key for an efficient Cu(I)‐iTMC‐LECs. All‐in‐all, this study provides fresh insights for the design of Cu‐iTMCs fueling research on sustainable ion‐based lighting sources. This study reports on the development and application of novel heteroleptic compounds in light‐emitting electrochemical cells (LECs). The compounds feature modified π‐conjugated pyridyl‐quinolyl N‐ and S‐bridged ancillary ligands, resulting in improved photophysical properties, such as red‐shifted emission and enhanced photoluminescence quantum yields. These improvements lead to LECs with promising stability and efficacy, representing 20‐fold enhancement compared to reference unsubstituted complexes.