Unraveling intra-aggregate structural disorder using single-molecule spectroscopy.

Area of Science:

• Molecular aggregates
• Supramolecular chemistry
• Optical spectroscopy

Background:

• Structural disorder in molecular aggregates significantly affects optical functionality.
• Ensemble measurements are insufficient for characterizing intra-aggregate structural disorder.
• Zinc-chlorin (ZnChl) nanotubular molecular aggregates exhibit spectral anomalies.

Purpose of the Study:

• To characterize intra-aggregate structural disorder in ZnChl nanotubes.
• To investigate the anomaly in linewidths between higher-energy and lower-energy absorption bands.
• To model the correlation of linewidths to understand structural variations.

Main Methods:

• Single-aggregate fluorescence excitation experiments.
• Linewidth analysis of absorption bands.
• Frenkel exciton modeling.

Main Results:

• Observed anomaly in linewidths: higher-energy bands are narrower than lower-energy bands.
• Correlation between linewidths of different bands was analyzed for individual aggregates.
• Frenkel exciton model successfully explained the observed linewidth correlations.

Conclusions:

• Small variations in molecular orientations within aggregates are the cause of the observed spectral anomalies.
• Single-aggregate spectroscopy combined with theoretical modeling is effective for probing structural disorder.
• Understanding structural disorder is crucial for controlling the optical functionality of molecular aggregates.