The 8‐Hydroxyquinolinium Cation as a Lead Structure for Efficient Color‐Tunable Ionic Small Molecule Emitting Materials. Issue 3 (3rd February 2023)

• Record Type: Journal Article
• Authors: Adranno, Brando; Renier, Olivier; Bousrez, Guillaume; Paterlini, Veronica; Baryshnikov, Glib V.; Smetana, Volodymyr; Tang, Shi; Ågren, Hans; Metlen, Andreas; Edman, Ludvig; Mudring, Anja-Verena; Rogers, Robin D.
• Is Part Of: Advanced photonics research. Volume 4:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-03
• Subjects: crystal engineering -- organic lighting -- photoluminescence -- secondary bonding interactions; Photonics -- Periodicals; 621.36505
• DOI: 10.1002/adpr.202200279
• Languages: English
• ISSNs: 2699-9293

Abstract

Abstract : Albeit tris(8‐hydroxyquinolinato) aluminum (Alq3 ) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand‐centered states, the use of metal‐free 8‐hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8‐hydroxyquinolinium cations into a solid rigid network with appropriate counter‐anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π ‐stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue‐green (488 nm). Time‐dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long‐lived S 1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C. Abstract : Synthesis of small molecules by a combination of 8‐hydroxyquinolinium and its 2‐ and 5‐methyl derivatives with bis(trifluoromethanesulfonyl)imide leads to easily accessible blue‐light ionic emitters. The hydrogen bond network and π‐stacking are recognized as the main reasons for the crystallization‐induced enhanced luminescence. High quantum yields (QYs) and long‐living excited states suggest they are excellent candidates for application in light‐emitting devices.