Chain Conformation and Exciton Delocalization in a Push-Pull Conjugated Polymer

Area of Science:

• Materials Science
• Physical Chemistry
• Polymer Science

Background:

• Linear and nonlinear optical line shapes provide insights into excitonic structure in polymer semiconductors.
• Understanding the relationship between spectral line shapes and chain conformation is key for optimizing optoelectronic properties.

Purpose of the Study:

• To investigate how spectral line shapes correlate with chain conformation in DPP-DTT, an electron push-pull copolymer.
• To explore the impact of polymer concentration on excitonic coupling and exciton coherence length.

Main Methods:

• Absorption, photoluminescence, and transient absorption spectroscopies were employed.
• Resonance Raman spectroscopy and ab initio calculations were used to deduce chain conformation.
• Viscosity measurements of polymer solutions were performed to identify gel formation concentration.

Main Results:

• Increased interchain excitonic coupling was observed above a critical polymer concentration.
• A red-shifted and line-narrowed photoluminescence spectrum indicated longer exciton coherence length.
• Changes in transient absorption spectra suggest new excited-state absorption or Stark effects.

Conclusions:

• Higher polymer concentrations lead to enhanced polymer chain order and increased exciton dispersion along the polymer backbone.
• Tuning microscopic chain conformation through concentration is a critical factor for polymer assembly in organic optoelectronics.
• This research offers insights for designing high-performance, large-area organic optoelectronic devices.