Structural effects on the optoelectronic properties of thermally activated delayed fluorescence materials: a computational approach

Date

2024-9-06

Author

Daştemir, Murat

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

91
views

88
downloads

Cite This

In this study, the effect of molecular structures on the thermally activated delayed fluorescence (TADF) mechanism was investigated. The research involved theoretical calculations on molecules that have demonstrated TADF properties experimentally, as well as their derivatives that may exhibit similar optoelectronic characteristics. Using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT), the ground state (S0), and excited states (S1 and T1) geometries of the molecules were determined. Key parameters, including the vertical and adiabatic singlet-triplet band gap (ΔEST), reorganization energy (λ), and spin-orbit coupling matrix elements (SOCME) were obtained. Reverse intersystem crossing (RISC) rate constants (kRISC) were derived using Fermi's Golden Rule and semiclassical Marcus theory with Franck-Condon approximation. The results show that in a D-A-D type symmetric molecule, replacing one symmetric donor with a stronger donor decreases the S1 and T1 transition energies. When the donor strengths differ significantly, the effect of the stronger donor to lower the S1 transition energy was found to be greater than the effect to lower the T1 transition energy, resulting in lower vertical ΔEST values. Conversely, replacing a donor with a weaker one in symmetric D-A-D structures increases both S1 and T1 transition energies without significantly changing ΔEST. Notably, incorporating a relatively weaker donor containing a heavy atom, as in PTZ, enhances the SOCME value, leading to higher RISC rate constants. Thus, using a relatively weaker donor with a heavy atom in asymmetric D-A-D* type molecules is identified as a promising strategy for developing efficient TADF molecules.

Subject Keywords

Thermally Activated Delayed Fluorescence, Density Functional Theory, Reverse Intersystem Crossing, Reorganization Energy, Spin-Orbit Coupling

URI

https://hdl.handle.net/11511/111390

Collections

Graduate School of Natural and Applied Sciences, Thesis