An In-Depth Quantum Chemical Investigation of INVEST TADF Dyes.

Area of Science:

• Organic electronics
• Photophysics
• Computational chemistry

Background:

• Designing organic emitters with inverted singlet-triplet (INVEST) gaps is key for efficient triplet harvesting in optoelectronics.
• Predicting the INVEST phenomenon requires reliable descriptors, which are currently scarce.

Purpose of the Study:

• To introduce and validate a new wave function-based descriptor, Qat, for predicting singlet-triplet inversion.
• To enable efficient screening of organic materials for optoelectronic applications.

Main Methods:

• Developed Qat descriptor from the transition density matrix to quantify short-range charge transfer and atomic-site charge localization.
• Performed systematic computational studies on N-triangulenes, extended π-systems, and nonalternant hydrocarbons.
• Calculated fluorescence (kf), intersystem crossing (kISC), and reverse intersystem crossing (kRISC) rate constants for INVEST dyes.

Main Results:

• Qat correlates with negative singlet-triplet gaps calculated at the SCS-CC2 level and shows similar trends at the TDA-DFT level.
• The Qat descriptor provides a reliable and universal metric for predicting INVEST, enabling cost-effective screening.
• INVEST dyes exhibit larger kRISC than kISC, with several exceeding 10^6 s^-1, indicating potential for efficient delayed fluorescence.
• Herzberg-Teller effects were found to dominate spin conversion processes in the studied INVEST dyes.

Conclusions:

• Qat is a versatile tool for INVEST design, bypassing the need for high-level correlated methods.
• The descriptor offers insights into the electronic structure-inversion relationship in organic emitters.
• This work advances the theoretical understanding of excited-state dynamics in INVEST systems and aids in designing efficient organic emitters.