Exciplex emissions derived from exceptionally long-distance donor and acceptor molecules

Area of Science:

• Organic electronics
• Photophysics
• Materials science

Background:

• Intermolecular electron-hole coupling is crucial for organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs).
• Typically, this coupling occurs over short distances (a few nanometers) between donor and acceptor molecules in excited states.

Purpose of the Study:

• To investigate and demonstrate exceptionally long-distance intermolecular electron-hole coupling.
• To characterize exciplex emissions in organic semiconductor films with a significant spacer layer.

Main Methods:

• Fabrication of donor/spacer (∼70 nm)/acceptor stacked films.
• Analysis of low-energy band emission spectra.
• Delayed transient photoluminescence (PL) and electroluminescence (EL) decay measurements.
• Photoluminescence quenching studies using oxygen.

Main Results:

• Observation of a distinct low-energy band emission, not attributable to individual components.
• Emission energy correlated with the highest occupied molecular orbital (HOMO) of the donor and lowest unoccupied molecular orbital (LUMO) of the acceptor.
• Delayed PL and EL decays confirmed exciplex characteristics.
• Oxygen quenching of the low-energy emission further supported exciplex formation.

Conclusions:

• Exceptionally long-distance exciplex emission (∼70 nm) was achieved between donor and acceptor molecules.
• This demonstrates a novel pathway for controlling exciplex formation over unprecedented distances in organic semiconductors.
• The findings have significant implications for designing advanced organic electronic devices like OLEDs and OPVs.