Chromophore Bending Controls Fluorescence Lifetime in Single Conjugated Polymer Chains

Area of Science:

• Polymer spectroscopy
• Photophysics
• Materials science

Background:

• Single-molecule spectroscopy provides detailed insights into conjugated polymers.
• Understanding the relationship between polymer structure and optical properties is crucial.

Purpose of the Study:

• To investigate how the spatial arrangement (twisting and bending) of monomer units in conjugated polymers influences their optical properties.
• To use β-phase polyfluorene as a model system to study intermonomeric coupling and its effect on optical transitions.

Main Methods:

• Single-molecule spectroscopy
• Analysis of single-photon polarization anisotropy
• Measurement of fluorescence lifetime

Main Results:

• Weak structural relaxation in the excited state leads to stochastic exciton self-trapping, reduced polarization anisotropy, and increased fluorescence lifetime, indicating π-system bending.
• Strong structural relaxation results in deterministic exciton localization, increased emission anisotropy, and decelerated fluorescence decay due to decreased exciton coherence length.

Conclusions:

• The nanoscale molecular shape of conjugated polymers significantly impacts their fundamental optical transitions.
• Single-molecule spectroscopy is a powerful tool for correlating structural dynamics with photophysical properties in polymers.