Geometrically isomeric [Ir(C^N)(C’^N’)(N’’^N’’’)]-tris-heteroleptic complexes versus [Ir(C^N)2(N’’^N’’’)]-bis-heteroleptic complex: towards High-performance near-infrared (NIR) polymer light-emitting diodes

Despite efficient NIR-OLEDs/PLEDs fabricated from [Ir(C^N)2(O^O)]/[Ir(C^N)2(N^O)]-bis-heteroleptic and few [Ir(C^N)(C’^N’)(O^O)]/[Ir(C^N)(C’^N’)(N^O)]-tris-heteroleptic iridium(III)-complexes, the problems to dissociation of N^O/O^O-ancillary units upon acid-hydrolysis or pyrolysis, together with geometrically isomeric complexity, have to be faced. Herein, a molecular design strategy to C1-symmetrical [[Ir(C^N)(C’^N’)(N’’^N’’’)]-tris-heteroleptic Ir(III)-complex (HC^N = Hiqbt, HC’^N’ = Hppy and HN’’^N’’’ = Hftrpz) is developed. The improved stability of [Ir(iqbt)(ppy)(ftrpz)] (2) is arisen from the strong HN’’^N’’’-ligand-field strength as compared to the N^O/O^O-ancillary counterparts. Meanwhile, owing to the Hftrpz-induced asymmetry, two geometrical isomers (2a and 2b) of [Ir(iqbt)(ppy)(ftrpz)] are first isolated. Noticeably, using the two isomeric NIR-phosphors [Ir(iqbt)(ppy)(ftrpz)]-a/b (2a and 2b) as the dopants, their high-performance NIR-PLEDs than that with the [Ir(iqbt)2(ftrpz)] (1) counterpart, are realized. Especially the NIR-PLED-2b, exhibits both an attractively high efficiency (ηEQEmax = 5.94%; λem = 692 nm) and almost negligible (< 5%) efficiency roll-off. And thus, this finding engenders [Ir(C^N)(C’^N’)(N’’^N’’’)]-tris-heteroleptic Ir(III)-complexes a new platform to the realization of high-performance, low-cost, large-area and scalable NIR-PLEDs.