Efficient light harvesting in dye-endcapped conjugated polymers probed by single molecule spectroscopy

Area of Science:

• Molecular spectroscopy
• Polymer physics
• Organic electronics

Background:

• Microscopic models of energy transfer in conjugated polymers often lack experimental validation.
• Understanding energy transfer requires single-molecule investigations to overcome ensemble averaging.
• Disorder (structural, temporal, energetic) significantly impacts energy transfer dynamics.

Purpose of the Study:

• To investigate energy transfer processes in dye-endcapped conjugated polymers at the single-molecule level.
• To resolve elementary processes of energetic relaxation in real-time.
• To elucidate the influence of molecular statistics on ensemble energy transfer efficiency.

Main Methods:

• Single molecule spectroscopy
• Real-time fluorescence measurements
• Polarization anisotropy analysis
• Temperature-dependent studies

Main Results:

• Highly efficient intramolecular energy transfer from polyindenofluorene backbone to perylene endcap observed.
• Energy transfer dynamics resolved in real-time, revealing backbone migration as rate-limiting.
• Analysis of spectral emission, polarization anisotropy, and fluorescence intermittency provided insights into chain conformation and energy transfer.
• Weak thermal activation suggests vibrational mode involvement in interchromophoric coupling.

Conclusions:

• Single-molecule statistics govern ensemble energy transfer efficiency in conjugated polymers.
• Backbone-endcap coupling is strong, but migration along the backbone limits intramolecular energy transfer.
• Findings are critical for understanding and mitigating exciton trapping on defects like fluorenone in polyfluorenes.