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

• Published in: Chemphyschem Vol. 24; no. 22; pp. e202300445 - n/a
• Main Authors: Nair, Aparna G., Das, Arathi, Chathoth, Nayana Edavan, Pratim Sarmah, Manash, Anjukandi, Padmesh
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 16-11-2023
• Subjects: Carbazole-Benzophenone Emitters; Carbazoles; Direct Singlet Harvesting mechanism; Emitters; Functional groups; Monomers; Nitrogen dioxide; Optical properties; Organic light emitting diodes; TADF; TDDFT
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.202300445

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 (ΔEST ≈0.12 eV), while the monomer (CzBP) (ΔEST≈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 ΔEST≈0.01 eV, projecting these systems as potential TADF‐active emitters. Furthermore, the chemical modification of CzBP‐LUMO alters the two‐step TADF mechanism (T1→T2→S1) in CzBP (ES₁>ET2>ET₁) to the Direct Singlet Harvesting (T1→S1) mechanism (ET2>ES₁>ET₁), which has recently been identified in the fourth‐generation OLED materials.
DFT/TDDFT calculations highlight the role of electron‐withdrawing substitutions on the benzophenone region in Carbazole‐Benzophenone (CzBP) non‐TADF emitter in making them TADF‐active.