Quantum chemical characterization and design of homoleptic Ir(III) complexes employing triphenylamine-featured thiazole-based ligand for efficient phosphors in OLEDs

The electronic structures and photophysical properties of a series of homoleptic Ir(III) complexes with triphenylamine-featured thiazole (1: fac-tris(2-phenylthiazole)iridium(III)) and benzothiazole (2: fac-tris[6-(1-naphthalenylphenylamino)-2-phenylbenzothiazole]iridium(III)) based ligands are investigated using the density functional method. By introducing the diphenylamine unit at 2-, 3- and 4-position of the phenyl ring in (C^N) ligands, 1a–1c (1a: fac-tris[2-(2-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1b: fac-tris[2-(3-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1c: fac-tris[2-(4-(N,N-diphenylamino)phenyl)thiazole]iridium(III)) and 2a–2c (2a: fac-tris[6-(1-naphthalenylphenylamino)-2-(2-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2b: fac-tris[6-(1-naphthalenylphenylamino)-2-(3-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2c: fac-tris[6-(1-naphthalenylphenylamino)-2-(4-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III)) are studied to get insight into the influence of different ligation positions of diphenylamine unit on the photophysical properties. The calculated results showed that the incorporation of diphenylamine unit into (C^N) ligands is beneficial to raise the HOMO levels, reducing the barrier height for hole injection and enhancing the balance of charge-transfer process. In addition, a remarkable color tuning could also be realized by altering the ligation positions of the diphenylamine units. A 82–132 nm blue shift is found for the thiazole-based 1a–1c compared with 1, while a relatively small red shift (7–35 nm) is observed on the emissions of benzothiazole-based 2a and 2c compared with 2. Meanwhile, a qualitative analysis on the parameters that would affect the quantum yields (ΦPL) of the studied complexes has also been presented.