Through-space charge-transfer emitters featuring high radiative decay rates for efficient organic light-emitting diodes

Abstract

Through-space charge-transfer (TSCT) emitters with high radiative decay rates are very important for their use in electroluminescent devices but have rarely been reported. Here, three TSCT emitters 1–3 with high radiative decay rates of over 107 s−1 are developed by using 4-methyl-9H-xanthene (MeXT) as the rigid linker, 10-phenyldihydroacridine (PhDMAC) as the donor, and 2,4,6-triphenyltriazine (1), 2,4,6-triphenylpyrimidine (2) and 2,4-di-tert-butyl-6-phenyl-1,3,5-triazine (3) as the acceptors. Single-crystal structures and theoretical calculations reveal that the donor fixed by the spiro-structure in MeXT and the acceptor located nearby the donor are arranged into a very close, cofacial packing with strong through-space electronic interactions, which promotes TSCT and the radiative decay of charge-transfer state. In degassed toluene solution, 1–3 show blue emission centered at 479, 458 and 455 nm, respectively, and afford high radiative decay rates (kr,s) of up to 1.6 × 107 s−1, which are the highest for TSCT emitters reported so far. In the doped films, 1–3 show high kr,s values of up to 1.3 × 107 s−1 and high photoluminescent efficiencies (ΦPL) of up to 0.95. Organic light-emitting diodes using 1–3 as the emitters afford blue emission with high external quantum efficiencies of up to 22.6%. The work reveals that TSCT emitters with similar emission characteristics (high ΦPL and high kr,s) to through-bond charge-transfer emitters are achievable by arranging the donor and acceptor units into a very close, cofacial packing.