Intramolecular Long-Range Charge-Transfer Emission in Donor-Bridge-Acceptor Systems

Area of Science:

• Photochemistry and Photophysics
• Supramolecular Chemistry
• Materials Science

Background:

• Charge recombination typically occurs nonradiatively, limiting energy transfer efficiency in molecular systems.
• Achieving efficient radiative charge recombination, especially over long distances, is a significant challenge in molecular design.

Purpose of the Study:

• To rationally design and synthesize donor-bridge-acceptor molecules capable of long-range intramolecular charge-transfer (CT) emission.
• To investigate the mechanisms and characteristics of this long-range CT emission, including its enhancement and spectral properties.
• To explore the potential applications of this phenomenon in molecular electronics and biomedical imaging.

Main Methods:

• Synthesis of novel donor-bridge-acceptor molecules with conjugated bridges.
• Spectroscopic characterization, including steady-state and time-resolved techniques (femtosecond transient absorption spectroscopy).
• Analysis of solvent dependence, temperature sensitivity, and emission polarization patterns to confirm CT emission identity.

Main Results:

• Demonstrated intramolecular charge-transfer (CT) emission through conjugated bridges up to 24 Å.
• Observed enhanced emission intensity via intensity borrowing, extending into the near-infrared (NIR) region.
• Confirmed efficient recombination fluorescence attributed to large excited-state electronic couplings and small energy gaps.

Conclusions:

• Successfully achieved unprecedented long-range intramolecular CT emission through rational molecular design.
• Established the definitive characteristics of this CT emission using multiple spectroscopic methods.
• Opened new avenues for utilizing long-range CT emission in molecular electronics and as biomedical imaging probes.