Tuning the twist angle of thermally activated delayed fluorescence molecules via a dendronization strategy: high-efficiency solution-processed non-doped OLEDs

Abstract

Two thermally activated delayed fluorescence dendrimers, named 2CzSO and 3CzSO, are designed and synthesized via dendronizing 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzo[b,d]thiophene-5,5-dioxide (1CzSO). By the dendronization strategy, two emitters acquire larger twist angles between electron donor and acceptor units compared with 1CzSO, resulting in a sequence of energy gaps between the lowest singlet and triplet states (ΔE_ST): 0.08 eV (3CzSO) < 0.12 eV (2CzSO) < 0.35 eV (1CzSO), and the order of DF lifetimes (τ_DF): 8.3 μs (3CzSO) < 14.2 μs (2CzSO) < 230 μs (1CzSO). Consequently, the non-doped solution-processed organic light-emitting device based on 2CzSO achieves a maximum external quantum efficiency of 10.7%, which is close to the highest values for non-doped solution-processed fluorescent OLEDs.