Highly efficient T-shaped deep-red thermally activated delayed fluorescence emitters: substitution position effect.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Achieving efficient deep-red thermally activated delayed fluorescence (TADF) emitters in the solid state remains a significant challenge.
• Modulating molecular structure is crucial for optimizing luminescence and charge transfer properties of TADF materials.
• Understanding structure-property relationships is key for developing advanced organic electronic devices.

Purpose of the Study:

• To theoretically investigate the solid-state light-emitting properties of a T-shaped molecule (pTPA-DPPZ).
• To compare the properties of pTPA-DPPZ with a Y-shaped analogue (oTPA-DPPZ).
• To elucidate the relationship between molecular structure and luminescence/charge transport in deep-red TADF emitters.

Main Methods:

• Combined quantum mechanics/molecular mechanics (QM/MM) method for electronic structure calculations.
• Thermal vibration correlation function (TVCF) theory to analyze excited-state properties.
• Kinetic Monte Carlo simulations for charge transport property assessment.

Main Results:

• pTPA-DPPZ exhibits a reduced HOMO-LUMO energy gap and red-shifted emission compared to oTPA-DPPZ.
• Enhanced transition dipole moment, increased radiative rate, and suppressed non-radiative energy loss in pTPA-DPPZ due to its molecular stacking.
• Superior TADF emission in pTPA-DPPZ, attributed to a larger spin-orbit coupling and smaller T2-S1 energy gap (0.1 eV); improved electron and hole mobilities due to close packing.

Conclusions:

• The T-shaped molecular design of pTPA-DPPZ effectively enhances luminescence and charge transport properties in the solid state.
• Suppression of molecular vibrations and optimized packing in pTPA-DPPZ are critical for reducing non-radiative decay and improving charge mobility.
• This study provides valuable insights for designing efficient non-doped deep-red TADF devices using T-shaped molecular architectures.