Efficient near-infrared emission benefits from slowing down the internal conversion process.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Developing organic deep-red (DR) and near-infrared (NIR) emitters with high photoluminescence quantum yield (PLQY) is challenging due to significant non-radiative decay (k_nr).
• Efficient electroluminescence in organic light-emitting diodes (OLEDs) requires minimizing energy loss pathways.

Purpose of the Study:

• To design and synthesize novel organic emitters with high PLQY for DR/NIR applications.
• To investigate the structure-property relationships governing efficient light emission in organic materials.
• To demonstrate the potential of molecular rigidity in enhancing exciton utilization efficiency (EUE) and electroluminescence.

Main Methods:

• Synthesis of TPANZPyPI and TPANZ3PI organic emitters.
• Photoluminescence quantum yield (PLQY) measurements.
• Theoretical calculations (e.g., internal conversion rates).
• Fabrication and characterization of non-doped and doped OLED devices.

Main Results:

• TPANZPyPI film achieved a high PLQY of 46.5% at 699 nm.
• Theoretical analysis revealed a small S1 to S0 internal conversion (IC) rate in TPANZPyPI, contributing to high NIR emission PLQY.
• TPANZPyPI's rigid structure suppressed the T2 to T1 IC process, improving exciton utilization efficiency (EUE).
• Non-doped OLEDs with TPANZPyPI showed NIR emission (4.6% max external quantum efficiency (EQEmax) @ 684 nm).
• Doped OLEDs exhibited DR emission (6.9% EQEmax @ 666 nm), among the highest for hybridized local charge transfer state materials >640 nm.

Conclusions:

• Increased molecular rigidity effectively suppresses excited state IC processes, in addition to S1 to S0 IC.
• This strategy leads to efficient electroluminescence in DR/NIR organic emitters.
• The developed emitters represent significant advancements for OLED applications requiring efficient red and near-infrared light emission.