Mesoscopic quantum emitters from deterministic aggregates of conjugated polymers.

Area of Science:

• Photophysics
• Materials Science
• Supramolecular Chemistry

Background:

• Fluorescence relies on discrete molecular entities emitting single photons.
• Understanding the size limits of molecular emitters is crucial for quantum applications.
• Conjugated polymers offer tunable optical properties for constructing molecular aggregates.

Purpose of the Study:

• To investigate the optical properties of growing deterministic aggregates from single conjugated polymer chains.
• To determine how large molecular objects can become while retaining single quantum emitter behavior.
• To differentiate between coherent and incoherent coupling mechanisms in polymer aggregates.

Main Methods:

• Fabrication of deterministic aggregates from single conjugated polymer chains.
• Spectroscopic analysis (fluorescence spectroscopy, lifetime measurements) to probe energy transfer and coupling.
• Mesoscale characterization of aggregate properties and comparison with isolated chains and bulk films.

Main Results:

• Aggregates with dozens of polymer chains function as single quantum emitters.
• Excitation energy transfer (EET) enhances brightness via increased absorption cross-section.
• Coherent coupling leads to a 10-fold increase in excited-state lifetime and spectral red shift.
• Incoherent Förster Resonance Energy Transfer (FRET) causes exciton quenching and blinking in larger aggregates.

Conclusions:

• Deterministic polymer aggregates maintain single quantum emitter characteristics up to a significant size.
• Coherent and incoherent coupling mechanisms have distinct spectroscopic signatures.
• Mesoscale studies reveal intermolecular interactions not observable in isolated chains or disordered bulk films.