Synthesis, Photophysical, and Electroluminescent Device Properties of Zn(II)‐Chelated Complexes Based on Functionalized Benzothiazole Derivatives

Abstract

Abstract New Zn(II)‐chelated complexes based on benzothiazole derivatives, including substituted functional groups such as methyl ( MeZn ), methoxy ( MeOZn ), or fluorenyl unit ( FuZn ), are investigated to produce white‐light emission. 2‐(2‐Hydroxyphenyl)benzothiazole derivatives in toluene and DMSO exhibit excited‐state intramolecular proton transfer (ESIPT), leading to a large Stokes shift of the fluorescence emission. However, in methanol they exhibit no ESIPT due to the intermolecular hydrogen bonding between the 2‐(2‐hydroxyphenyl)benzothiazole derivative and methanol. Their Zn(II)‐chelated complexes exhibit the absorption band red‐shifted at 500 nm in nonpolar solvent and the absorption band blue‐shifted at about 420 nm in protic solvent. In multilayer electroluminescent devices, methyl‐substituted Zn(II)‐chelated complex ( MeZn ) exhibits excellent power efficiency and fluorene‐substituted Zn(II)‐chelated complex ( FuZn ) has a high luminance efficiency (1 cd m −2 at 3.5 V, 10 400 cd m −2 at 14 V). The EL spectra of Zn(II)‐chelated complexes based on benzothiazole derivatives exhibit broad emission bands. In addition, their electron‐transport property for red–green–blue (RGB) organic light‐emitting diodes (OLEDs) is systematically studied, in comparison with that of Alq 3 . The results demonstrate the promising potential of MeZn as an electron‐transporting layer (ETL) material in preference to Alq 3 , which is widely used as an ETL material.