Stable Luminescent Radicals with Efficient Through-Space Charge-Transfer Emission

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Luminescent radicals with donor-radical (D-R) charge-transfer (CT) excited states are crucial for optoelectronics.
• Previous research primarily focused on through-bond charge-transfer (TBCT) mechanisms.

Purpose of the Study:

• To report the first luminescent radicals based on tris(2,4,6-trichlorophenyl)methyl radical (TTM) utilizing through-space charge-transfer (TSCT) excited states.
• To demonstrate the potential of TSCT as a design strategy for high-performance and stable luminescent radicals.

Main Methods:

• Synthesis of novel luminescent radicals: TPA-FR-TTM and CZP-FR-TTM.
• Characterization of their photophysical properties, including photoluminescence quantum efficiency (PLQE) and non-radiative decay rates.
• Investigation of electronic structures and radical stability.

Main Results:

• CZP-FR-TTM achieved a high PLQE of 64.3% and an ultralow non-radiative decay rate (1.3 × 10^6 s^-1).
• Spatial separation in TSCT minimizes electron-vibrational coupling, suppressing non-radiative decay.
• Reduced electronic coupling enhances radical stability by leading to non-Aufbau electronic structures.

Conclusions:

• Through-space charge-transfer (TSCT) is a viable and powerful strategy for developing high-performance luminescent radicals.
• This work opens new avenues for designing stable, open-shell optoelectronic materials.
• The findings challenge previous assumptions and expand the scope of radical-based optoelectronics.