Tris-heteroleptic Ir(iii)-complexes With One Strong N^O-ancillary π ...

C1-Symmetrical [Ir(C^N1)(C^N2)(N^O)]-tris-heteroleptic Ir(iii)-complexes with one strong N^O-ancillary π-donor for efficient all-solution-processed near-infrared (NIR) polymer light-emitting diodes (PLEDs)†

Yan Zhang,‡a Baoweng Wang,‡a Jiaxiang Liu,a Xingqiang Lü, *a Guorui Fu,*ab Wentao Li*ab and Wai-Yeung Wong *b Author affiliations

* Corresponding authors

a School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi, China E-mail: [email protected], [email protected]

b Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China E-mail: [email protected], [email protected]

Abstract

Among reliable vacuum-deposited or solution-processed NIR-OLEDs/PLEDs doped with NIR-emitting iridium(III)-complexes, high-performance achievement of their all-solution-processed NIR-PLEDs remains a great challenge. In this study, owing to the forceful electronic perturbation achieved by incorporation of the strong π-donating N^O-ancillary ligand Hpbi, its NIR-emitting tris-heteroleptic [Ir(iqbt)(btp)(pbi)] (2) does not exhibit an augmented 3MLCT effect in comparison to the corresponding bis-heteroleptic [Ir(iqbt)2(pbi)] (1) counterpart. Nonetheless, the transition dipole (TD) effect through kr ∈ TD2 dominates, rendering the kr and the resulting ΦPL (0.36; λem = 714 nm) of 2 larger than those of 1 (ΦPL = 0.29; λem = 712 nm). Moreover, through electron injection/transport facilitated by the composite cathode Ba/Al instead of LiF/Al, better electroluminescent properties (ηMaxEQE = 3.53 (1) versus 4.24% (2) and negligible (<5%) efficiency roll-off) are realized for their all-solution-processed NIR-PLEDs. This result shows that: (i) both the 3MLCT and TD effects should be simultaneously taken into account in challenging the intrinsic low-efficiency of Ir(III)-complex-based NIR-emitters; (ii) in dependent on electron injection/transport facilitation with one specific composite cathode, high-performance and reliable all-solution-processed NIR-PLEDs especially based on [Ir(C^N1)(C^N2)(L^X)]-tris-heteroleptic Ir(III)-complexes could desirably be approached.

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