Time-Dependent Structure Assessment of Conjugated Polymer Aggregates in Solution by Single-Molecule Fluorescence...

Area of Science:

• Materials Science
• Polymer Chemistry
• Spectroscopy

Background:

• Understanding aggregation kinetics of n-type polymers is crucial for controlling ink properties.
• Favorable aggregation impacts shelf life, printability, and thin-film performance of conjugated polymers.

Purpose of the Study:

• To characterize the in situ aggregation kinetics of n-type copolymers.
• To identify and analyze subcategories of aggregates using advanced spectroscopy.

Main Methods:

• Ensemble absorbance and fluorescence spectroscopy for spectral characterization.
• Single-molecule fluorescence spectroscopy, specifically a diffusion-based single-molecule burst method.
• Polarization-sensitive single-molecule fluorescence spectroscopy and spectral decomposition.

Main Results:

• P-(EO-NDIT2) copolymers self-assemble into nano- to micrometer-sized aggregates over weeks to months.
• Aggregates were categorized into small (Rh ≈ 60 nm) and large (Rh ≈ 300 nm) sizes.
• Increased aggregate size correlated with enhanced fluorescence brightness, red-shifted emission, and greater internal order.

Conclusions:

• Single-molecule spectroscopy provides detailed insights into polymer aggregate formation and evolution.
• Aggregate size influences optical and structural properties, potentially due to crystalline domain alignment and backbone planarization.
• Controlling aggregation kinetics is vital for optimizing n-type polymer applications.