Through versus cross electron delocalization in polytriacetylene oligomers: a computational analysis

Area of Science:

• Theoretical Chemistry
• Materials Science
• Organic Electronics

Background:

• Polytriacetylenes (PTAs) and iso-polytriacetylenes (iso-PTAs) are conjugated polymers with distinct pi-electron systems.
• Understanding conjugation pathways is crucial for designing novel electronic materials.

Purpose of the Study:

• To systematically investigate and compare the molecular and electronic properties of PTA and iso-PTA oligomers.
• To analyze the impact of through- versus cross-conjugation on electronic structure and properties.
• To explore the behavior of these oligomers in neutral, anionic, and cationic states.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Computation of molecular geometries, electron affinities, ionization potentials, and excitation energies.
• Analysis of nonlinear optical properties for oligomers up to the nonamer.

Main Results:

• Iso-PTA oligomers exhibit constant bond lengths in neutral states, with energy gap reduction due to correlation.
• Frontier orbitals in iso-PTAs delocalize along the backbone, indicating cross-conjugation effects.
• Oxidation or reduction of iso-PTAs significantly alters bond lengths and activates cross-linked pi-delocalization.
• Effective conjugation length is observable-dependent.

Conclusions:

• Pi-delocalization can extend through cross-linked carbon atoms in iso-PTA systems.
• Charge state plays a critical role in enabling cross-conjugation in iso-PTA oligomers.
• The study provides insights into structure-property relationships for conjugated organic materials.