Synthesis and Photophysical Properties of TADF Compounds with Planarized Boron-Carbonyl Hybrid Acceptors

Abstract

Thermally activated delayed fluorescence (TADF) with a fast reverse intersystem crossing (RISC) gives a great challenge to attain a high efficiency in OLED device performances. Since it has been demonstrated that strong spin orbit coupling (SOC) could facilitate a fast RISC, we designed and synthesized a series of boron-carbonyl hybrid compounds comprising 10H-phenoxazine as a fixed donors connected with different acceptors, boranthracenone (PXZBAO), boratetracenone (PXZBTO), and borapentacenone (PXZBPO). All compounds have small singlet-triplet energy splitting (EST < 0.1 eV), very short-lived delayed fluorescence lifetime (d < 2 μs), and high kRISC of ca. 106 s−1, which supported the strong and efficient TADF properties. In particular, the compounds exhibited blue-shifted emission wavelength (PL = 619574 nm) and (PL = 609568 nm) in both toluene and host film respectively by the addition of the naphthyl group in the boron acceptors. This finding suggests that the 3nπ* from boron-carbonyl units was gradually changed to 3ππ* as the number of the naphthyl ring increased. Likewise, the role of 3nπ* from boron-carbonyl unit lies on the T2 level inducing strong SOC with the 1CT (S1) state so that the fast RISC could be accelerated. The details of synthesis, characterization, photophysical properties and theoretical studies will be discussed.