Anti-concentration quenching violet-blue TADF OLEDs via indirect conformal distributions tuning in solid-state

Controlling conformation distributions is the key to manipulate material properties of multi-conformal molecules. Distinct from previous strategy with direct change or impact on the flexible groups, we tune the conformation distribution through changing peripheral groups to influence their intermolecular interactions. Two blue violet TADF emitters, namely tert-butyl substituted 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azagermine (TDBA-PAG) and cumenyl substituted 5-(2,12-bis(2-phenylpropan-2-yl)-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azagermine (TPDBA-PAG) were designed and synthesized. With the same germanium-integrated donor, the two compounds show similar emission properties in solution with calculated conformation dominantly of their quasi-axial (QA) forms (> 97%). However, TPDBA-PAG presents a lower QA ratio compared with TDBA-PAG, which endows the former with more pronounced TADF emission, higher emission efficiency and reduced concentration quenching phenomena in solid state. As a result, TPDBA-PAG performed as one of the best non-doped and doped violet-blue emitters and successfully sensitized MesB-DIDOBNA-N to achieve record high EQEmax of 24.7% at 406 nm, making significant progress in NUV OLEDs.