Force Fields for Macromolecular Assemblies Containing Diketopyrrolopyrrole and Thiophene

Area of Science:

• Materials Science
• Computational Chemistry
• Organic Electronics

Background:

• Conjugated polymers and molecular crystals containing diketopyrrolopyrrole, thiophene, and thieno[3,2-b]thiophene units exhibit low band gaps, leading to high photovoltaic device efficiency.
• Accurate computational modeling is crucial for understanding the structure-property relationships governing the performance of these materials.

Purpose of the Study:

• To develop and validate new, systematically parametrized force fields for large conjugated systems, including polymers and molecular crystals.
• To investigate the structural, dynamic, and electronic properties of these materials and their building blocks.
• To assess the suitability of the new force fields for electronic property calculations.

Main Methods:

• A force-matching procedure was employed to parametrize new force fields for conjugated systems.
• Computational modeling included equilibrium structure, force, and energy calculations for chromophore building blocks.
• Classical and ab initio molecular dynamics simulations were performed, coupled with time-dependent density functional theory (TDDFT) for electronic property analysis.

Main Results:

• The new force fields accurately reproduce equilibrium structures, forces, and energies of chromophores compared to reference electronic structure methods.
• Simulations revealed high planarity and π-π stacking in polymers and crystals, promoting charge transport.
• Analysis showed negligible fluctuations in the density of states for conducting polymers and identified low-frequency vibrations modulating excitonic coupling in molecular crystals.

Conclusions:

• The developed force fields provide a reliable method for studying large conjugated systems.
• The findings elucidate the molecular-level origins of high efficiency in these photovoltaic materials.
• This approach enables direct investigation of structure-property relationships for designing advanced organic electronic materials.