Linking Emission Bandwidth to Charge-Resonance Character in B/O-Based Multiple-Resonance Emitters

Area of Science:

• Materials Science
• Organic Electronics
• Computational Chemistry

Background:

• High-color-purity organic light-emitting diodes (OLEDs) require narrowband emission.
• Predicting emission full width at half-maximum (fwhm) from molecular structure is challenging.
• Multiple-resonance (MR) emitters offer potential for improved OLED performance.

Purpose of the Study:

• To develop a rapid prediction method for emission fwhm in MR emitters.
• To introduce an effective descriptor for charge-resonance balance (c_eff²).
• To establish a computationally economical approach for assessing spectral narrowing.

Main Methods:

• Adaptation of the cyanine limit two-state framework.
• Calculation of c_eff² from state and transition dipole moments at Franck-Condon geometry.
• Correlation analysis of c_eff² with experimental fwhm in different solvent polarities.

Main Results:

• A strong inverse linear correlation (R² = 0.997) was found between $\sqrt{c_{eff}^2}$ and experimental fwhm for DOBNA derivatives in dichloromethane.
• The negative trend was retained in toluene (R² = 0.925), though more scattered due to solvent polarity.
• Excitation-induced dipolar reorganization magnitude, not just transition dipole moment, governs fwhm variation.

Conclusions:

• c_eff² is a physically interpretable and computationally economical descriptor for spectral narrowing in DOBNA-based MR emitters.
• The descriptor facilitates rapid prediction of fwhm, crucial for designing high-color-purity OLEDs.
• This work advances the understanding of structure-property relationships in organic electronic materials.