Circularly Polarized Organic Long-Persistent Luminescence from Chiral Binaphthyl Guests

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Organic long-persistent luminescence (OLPL) and circularly polarized luminescence (CPL) are advanced optical phenomena with diverse applications.
• Developing materials that combine both OLPL and CPL properties presents significant challenges.
• Chiral molecules are crucial for achieving CPL, but integrating them into OLPL systems requires careful molecular design.

Purpose of the Study:

• To achieve the first organic long-persistent luminescence (OLPL) materials exhibiting circularly polarized luminescence (CPL) characteristics.
• To design and synthesize novel axially chiral molecules as guest dopants for OLPL matrices.
• To investigate the photophysical properties and potential applications of these new CPL-OLPL systems.

Main Methods:

• Design and synthesis of two pairs of axially chiral molecules ((R/S)-BINAC guests) with specific structural features (unlocked chiral binaphthyl backbones, phenyl-carbazole moieties).
• Doping these chiral guests into a poly(ethylene glycol terephthalate) (PET) matrix to form CPL-OLPL systems.
• Characterization of luminescence properties, including dissymmetry factor (g_lum), phosphorescence efficiency (Φp), and luminescence lifetime.
• Extension of OLPL characteristics into the near-infrared (NIR) region using Förster resonance energy transfer (FRET) with an NIR dye.

Main Results:

• Successfully created the first CPL-OLPL systems by doping chiral (R/S)-BINAC molecules into a PET matrix.
• The designed chiral guests exhibited high intersystem crossing (ISC) efficiencies and suitable triplet energy levels to prevent quenching.
• The resulting CPL-OLPL systems demonstrated a dissymmetry factor (g_lum) of 10^-3, a high phosphorescence efficiency (Φp) of 12.8%, and an exceptionally long lifetime of over 4000 seconds (>1 hour).
• The OLPL properties were successfully extended to the NIR region via FRET.

Conclusions:

• The study presents the first successful examples of organic long-persistent luminescence (OLPL) materials with circularly polarized luminescence (CPL) characteristics.
• Careful molecular design of chiral guests, like the (R/S)-BINAC derivatives, is a viable strategy for developing advanced CPL-OLPL systems.
• These novel materials offer potential for expanded applications in areas requiring both long-lasting and circularly polarized light emission, including advanced displays, sensors, and anticounterfeiting technologies.