Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll‐Off

Abstract

In this work, we present how a small change in molecular structure can affect the electrochemical stability of organic compounds. A new electron donor–acceptor–donor–acceptor (D–A–D–A) macrocyclic π‐conjugated compound ( t BuMC ) comprising of dibenzophenazine as As and N,N‐ bis( t ‐butylphenyl) ‐p ‐phenylenediamines as Ds has been synthesized. The photophysical investigation uncovered that t BuMC showed thermally activated delayed fluorescence and that the organic light‐emitting diodes (OLEDs) fabricated with t BuMC as the emitter achieved high external quantum efficiency (EQEs) of ca. 10%. However, the OLED with t BuMC showed a slightly lower EQE than that of the OLED with MC (11.6%) and showed greater EQE roll‐off. Comparative studies on electrochemical properties of t BuMC , MC , and a linear analogue ( Linear ) revealed the introduction of t ‐Bu groups in the D–A–D–A scaffold causes a significant change in redox behaviour. Full electrochemical and spectroelectrochemical studies gave clues to understand how the steric hindering group is affecting the charge distribution in the new molecules which results in a significant difference in the OLED roll‐off. The electrochemical investigations together with UV‐Vis‐NIR and EPR analyses supported by quantum chemical theoretical calculations were performed, which provided us insights on the effect of structural modification on the redox properties of the D–A–D–A scaffold.