Chemical Tailoring Assisted non-TADF to TADF Switching in Carbazole-Benzophenone Emitter - An In-silico Investigation

Organic light-emitting diodes (OLEDs) have become one of the most popular lighting technologies since they offer several advantages over conventional devices. In carbazole-benzophenone (CzBP) OLED devices, the polymeric form of the compound is previously reported to be Thermally Activated Delayed Fluorescence (TADF)-active (Delta E-ST approximate to 0.12 eV), while the monomer (CzBP) (Delta E-ST approximate to 0.39 eV) does not. The present study examines the effect of chemical tailoring on the optical and photophysical properties of CzBP using DFT and TDDFT methods. The introduction of a single -NO2 group or di-substitution (-NO2, -COOH or -CN) in the selected LUMO region of the reference CzBP monomer significantly reduces Delta E-ST approximate to 0.01 eV, projecting these systems as potential TADF-active emitters. Furthermore, the chemical modification of CzBP-LUMO alters the two-step TADF mechanism (T-1 -> T-2 -> S-1) in CzBP (E-S1 > E-T2 > E-T1) to the Direct Singlet Harvesting (T-1 -> S-1) mechanism (E-T2 > E-S1 > E-T1), which has recently been identified in the fourth-generation OLED materials.

Automated summary

This study investigates the effect of chemical tailoring on the optical and photophysical properties of CzBP and finds that the introduction of a single -NO2 group or di-substitution can make it a potential TADF-active emitter. The study also reveals the change in the TADF mechanism due to the chemical modification of CzBP-LUMO.