Pyridine-, Pyrimidine-, and Triazine-Based Thermally Activated Delayed Fluorescence Emitters

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials are crucial for efficient organic light-emitting diodes (OLEDs).
• Tuning the electronic properties of TADF emitters is key to achieving desired emission colors and efficiencies.
• The number of nitrogen atoms in electron acceptor units can significantly influence the photophysical properties of TADF molecules.

Purpose of the Study:

• To design and investigate novel TADF materials incorporating pyridine, pyrimidine, and triazine as electron acceptors and carbazole as an electron donor.
• To explore the effect of varying the number of nitrogen atoms in the acceptor units on the electronic and optical properties.
• To evaluate the suitability of these novel materials for blue organic light-emitting diode (OLED) applications.

Main Methods:

• Computational design of novel TADF materials: TmCzPd, TmCzPm, and TmCzTrz.
• Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) calculations were employed.
• Analysis of electron distribution (HOMO, LUMO) and excited state energies (S1, T1) to determine energy differences (ΔEST).

Main Results:

• Calculated smaller energy differences (ΔEST) between singlet (S1) and triplet (T1) excited states for TmCzPm (0.200 eV) and TmCzTrz (0.186 eV) compared to TmCzPd (0.395 eV).
• TmCzPm exhibited a suitable emission wavelength of 473.1 nm with significant oscillator strength.
• The reduced ΔEST values indicate efficient reverse intersystem crossing (RISC) for TADF operation.

Conclusions:

• The number of nitrogen atoms in the electron acceptor unit plays a critical role in tuning the photophysical properties of TADF materials.
• TmCzPm demonstrates significant potential as an efficient blue OLED emitter due to its small ΔEST and favorable emission characteristics.
• These findings provide valuable insights for the rational design of high-performance TADF materials for next-generation displays and lighting.