Hyperconjugation Engineering of π-Extended Azaphosphinines for Designing Tunable Thermally Activated Delayed...

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Organic π-conjugated molecules (OCMs) are crucial for optoelectronic applications.
• Tuning OCM properties often involves heteroatom incorporation.
• Developing novel OCMs with enhanced photophysical properties is an ongoing research area.

Purpose of the Study:

• To introduce a new family of 1,4-azaphosphinines with extended σ-π hyperconjugations.
• To investigate the photophysical properties, particularly thermally activated delayed fluorescence (TADF).
• To explore the potential of σ-π hyperconjugation as a design strategy for OCMs.

Main Methods:

• Synthesis of 1,4-azaphosphinine derivatives with tunable p-centers.
• Photophysical studies including fluorescence spectroscopy and quantum yield measurements.
• Computational analysis: Orbital localization and Natural Bond Orbital (NBO) analysis.

Main Results:

• Azaphosphinines demonstrated narrow-band TADF (26-40 nm FWHM) with emission spanning UV-blue to green.
• Effective σ*-π* hyperconjugation was identified as the origin of multiple-resonance (MR) TADF.
• High photoluminescence quantum yields (PLQYs) up to 92% were achieved.
• Organic light-emitting diodes (OLEDs) fabricated with these materials showed narrow-band UV/deep-blue emission and high external quantum efficiency (EQE) up to 10.3%.

Conclusions:

• σ-π hyperconjugation is a viable strategy for inducing MR-TADF, distinct from traditional p-π conjugation.
• The developed azaphosphinines offer tunable TADF properties and high efficiencies.
• This work presents a new pathway for designing advanced OCMs for lighting and display applications.