Computational study on 8-quinolinolato-alkali, an electron transporting material for OLED devices

Abstract

Organic light-emitting diodes (OLEDs) materials have occupied significance in device applications due to their lightweight, thin, quick switching speed, flexible, easy to fabricate and low-cost features. The 8-quinolinolato-lithium (Liq) is commonly used as an electron injector in the layer of OLEDs. Herein, we study 8-quinolinolato-sodium (Naq) and 8-quinolinolato-potassium (Kq) and compare them with Liq using density functional theory approach. We analyze the molecular structure of 8-quinolinolate-alkali (Mq) for M=Li, Na and K and notice that the structure of Mq remains planar for all the three substitutions. The increased dipole moments of Mq with the change of substitution (M) suggest that its enhanced solubility in polar solvents, which tends to reduce the electron injection barrier. Furthermore, the higher polarizability of Naq and Kq indicates that the molecule is chemically more reactive than Liq and therefore, is expected to respond quickly when the field is applied. Moreover, the electron affinities of Mq increase with the substitution of Na and K, which is also desirable for improved electron transport behavior. However, the reorganization energy of Naq and Kq is slightly higher than that of Liq, which is not desirable for the transport of charge carriers in OLED devices. Therefore, the findings of this study demand further assessment for the application of Naq and Kq instead of Liq in OLED devices.