Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X

Salthouse, Rebecca J.; Pander, Piotr; Yufit, Dmitry S.; Dias, Fernando B.; Williams, J.A. Gareth

Abstract

We present a study of aggregate excited states formed by complexes of the type Pt(N^C^N)X, where N^C^N represents a tridentate cyclometallating ligand, and X = SCN or I. These materials display near-infrared (NIR) photoluminescence in film and electroluminescence in NIR OLEDs with λmaxEL = 720–944 nm. We demonstrate that the use of X = SCN or I modulates aggregate formation compared to the parent complexes where X = Cl. While the identity of the monodentate ligand affects the energy of Pt–Pt excimers in solution in only a subtle way, it strongly influences aggregation in film. Detailed calculations on aggregates of different sizes support the experimental conclusions from steady-state and time-resolved luminescence studies at variable temperatures. The use of X = I appears to limit aggregation to the formation of dimers, while X = SCN promotes the formation of larger aggregates, such as tetramers and pentamers, leading in turn to NIR photo- and electroluminescence > 850 nm. A possible explanation for the contrasting influence of the monodentate ligands is the lesser steric hindrance associated with the SCN group compared to the bulkier I ligand. By exploiting the propensity of the SCN complexes to form extended aggregates, we have prepared an NIR-emitting OLED that shows very long wavelength electroluminescence, with λmaxEL = 944 nm and a maximum EQE = 0.3 ± 0.1%. Such data appear to be unprecedented for a device relying on a Pt(II) complex aggregate as the emitter.

Citation

Salthouse, R. J., Pander, P., Yufit, D. S., Dias, F. B., & Williams, J. G. (2022). Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X. Chemical Science, 13(45), 13600-13610. https://doi.org/10.1039/d2sc05023d

• Journal Article Type: Article
• Acceptance Date: Oct 24, 2022
• Online Publication Date: Nov 11, 2022
• Publication Date: 2022
• Deposit Date: Feb 20, 2023
• Publicly Available Date: Feb 20, 2023
• Journal: Chemical Science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 13
• Issue: 45
• Pages: 13600-13610
• DOI: https://doi.org/10.1039/d2sc05023d
• Public URL: https://durham-repository.worktribe.com/output/1181615