The coordinated tunning optical, electrical and thermal properties of spiro-configured phenyl acridophopsphine oxide and sulfide for host materials

Two spiro-configured phenyl acridophopsphine-based oxide and sulfide host materials, named 5-phenyl-5H-spiro[acridophosphine- 10,9′-fluorene]-5-oxide (PSAFO) and 5-phenyl-5H-spiro [acridopho-sphine-10,9′-fluorene]5-sulfide (PSAFS), were synthesized by convenient method. The lowest unoccupied molecular orbital (LUMO) energy level and electron mobility could be decreased and improved as the S-atom replaced O-atom, respectively. Then, the electron injecting/transporting ability of PSAFS is expected to be enhanced. Moreover, the S-atom would provide PSAFS with better electron-donating capability and heavier molecular weight compared with that of PSAFO. Thus, a higher HOMO (the highest occupied molecular orbital) energy level and thermal stability can be achieved due to the shallower onset of oxidation potential and increased molecular weight. Consequently, a narrower energy gap between HOMO and LUMO of PSAFS would be obtained, and its thermal stability could be improved, which is beneficial to constructing high performance device. Although the frontier molecular orbitals and thermal stability were finely controlled by molecular modification, the high triplet (T1) energy level was still retained due to the limited π-conjugation. With the high T1, HOMO and LUMO energy levels of 2.83/2.82, −6.19/-5.66 and −2.12/-2.19 eV, PSAFO and PSAFS based blue TADF OLEDs with low driving voltages of 2.9/3.1 V and maximum EQEs of 12.4/13.8% are successfully realized.