A donor-acceptor cage for circularly polarized TADF emission

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials are crucial for efficient organic light-emitting diodes (OLEDs).
• Achieving circularly polarized emission (CPE) in TADF emitters is challenging but desirable for advanced display and sensing applications.
• Chiral molecules offer unique photophysical properties, but their integration into efficient TADF systems is an active research area.

Purpose of the Study:

• To report the first chiral donor-acceptor (DA) cage molecule, DA-2, exhibiting efficient circularly polarized thermally activated delayed fluorescence (CP-TADF).
• To investigate the structure-property relationships governing the CP-TADF performance in the designed DA-2 molecule.
• To establish a novel design strategy for developing new chiral CP-TADF emitters.

Main Methods:

• Synthesis and characterization of the chiral donor-acceptor cage molecule DA-2.
• Photophysical measurements including photoluminescence quantum yield (PLQY) and circularly polarized luminescence (CPL) spectroscopy.
• Analysis of the energy levels, specifically the singlet-triplet energy gap (ΔE_ST), and transition dipole moments to understand the mechanism of CP-TADF.

Main Results:

• DA-2 demonstrated efficient CP-TADF with |g_lum| values up to 2.1 × 10^-3 and a photoluminescence quantum yield (PLQY) of 32%.
• A small singlet-triplet energy gap (ΔE_ST) of 0.051 eV was achieved, facilitating efficient reverse intersystem crossing.
• Quasi-parallel alignment (θ = 6°) of transition electric and magnetic dipole moments, arising from through-space charge transfer, was observed, crucial for CP-TADF.

Conclusions:

• The chiral DA-2 cage represents the first example of an efficient CP-TADF emitter based on a donor-acceptor cage architecture.
• The through-space charge transfer interaction in the quasi-parallel D-A configuration is a viable strategy for achieving high-performance CP-TADF.
• This work provides a novel design paradigm for the development of next-generation chiral light-emitting materials.