The relationship between structure and excited-state properties in polyanilines from geminal-based methods.

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Polyanilines (PANIs) are conductive polymers with tunable properties.
• Understanding structure-property relationships is crucial for PANI applications.
• Accurate theoretical methods are needed to interpret PANI electronic and vibrational spectra.

Purpose of the Study:

• To investigate the structure-to-property relationship in polyanilines (PANIs) of varying lengths and oxidation states.
• To analyze the electronic and vibrational spectroscopy of leucoemeraldine, emeraldine, and pernigraniline tetramers and octamers.
• To assess the accuracy of Density Functional Approximations (DFAs) against high-level wavefunction methods and experimental data.

Main Methods:

• Employed various Density Functional Approximations (DFAs) for structural properties, energies, and spectra.
• Performed large-scale orbital-optimized pair-Coupled Cluster Doubles (oo-pCCD) for ground and excited states.
• Utilized Configuration Interaction Singles (CIS) for excited states and EOM-pCCD+S for detailed transition analysis, alongside quantum informational analysis.

Main Results:

• Identified charge transfer and local electronic transitions in PANIs using EOM-pCCD+S, which is not feasible with canonical molecular orbitals from DFAs.
• Demonstrated that charge transfer excitations dominate the low-lying spectra of emeraldine and pernigraniline.
• Showed that increasing polymer length alters the nature of the primary electronic transitions in PANIs.

Conclusions:

• Advanced quantum chemistry methods, particularly EOM-pCCD+S, provide deeper insights into PANI electronic structure than standard DFAs.
• The study elucidates the role of charge transfer and polymer elongation in dictating PANI spectral properties.
• Findings contribute to a better understanding of polyaniline electronic behavior for tailored material design.