Theoretical Study on Selective Isotope Substitution Boosting High-Performance Circularly Polarized Delayed...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Isotope effect is a novel strategy for enhancing organic light-emitting diode (OLED) performance.
• A theoretical framework is needed to understand how isotopic engineering impacts circularly polarized thermally activated delayed fluorescence (CP-TADF) emitters.
• Understanding the relationship between isotopic substitution and CP-TADF properties is crucial for designing efficient optoelectronic devices.

Purpose of the Study:

• To investigate the impact of isotopic substitution on the performance of CP-TADF emitters.
• To elucidate the theoretical mechanisms behind isotope-induced enhancements in CP-TADF properties.
• To provide insights for the rational design of advanced circularly polarized luminescence (CPL) optoelectronic materials.

Main Methods:

• Design and synthesis of four isotopically substituted isomers based on resonance Raman (rR) spectroscopic analysis.
• Theoretical calculations within the Herzberg-Teller (HT) limit to determine excited-state properties.
• Analysis of circularly polarized luminescence (CPL) rates (kCPL), CPL dissymmetry factors (gCPL), and nonradiative internal conversion rates (kIC).

Main Results:

• All isotopic isomers showed a 3-orders-of-magnitude enhancement in kCPL rates compared to the Franck-Condon (FC) approximation.
• Donor-acceptor substituted isomers Czp-DiKTa-18O/D and Czp-DiKTa-D exhibited significantly enhanced gCPL factors (1.96 × 10-1 and 1.21 × 10-1, respectively).
• Isotopic substitution suppressed kIC rates, leading to substantially improved delayed circularly polarized quantum yields (ΦDCPL) for Czp-DiKTa-18O/D (93%) and Czp-DiKTa-D (91%).

Conclusions:

• Selective isotope substitution is a highly effective strategy for simultaneously enhancing kCPL, gCPL, and ΦDCPL in CP-TADF emitters.
• The study provides valuable theoretical insights into the mechanisms driving isotope-induced performance improvements.
• These findings pave the way for the rational design of next-generation CPL optoelectronic materials with superior efficiency.