A three-state effective Hamiltonian for symmetric cationic diarylmethanes

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Cationic diarylmethanes, derivatives of Michler's Hydrol Blue, exhibit unique electronic properties.
• Understanding their low-energy electronic structure is crucial for designing novel dyes and materials.

Purpose of the Study:

• To analyze the low-energy electronic structure of symmetric cationic diarylmethanes.
• To investigate the impact of bridge substitution on electronic properties and charge distribution.

Main Methods:

• Employed a four-electron, three-orbital complete active space self-consistent field (CASSCF) model.
• Utilized multi-state multi-reference perturbation theory (MS-MRPT) to compute a three-state diabatic effective Hamiltonian.
• Applied an isolobal analogy to map electronic structures onto analogous diabatic states.

Main Results:

• Identified diabatic states analogous to classical resonance structures, including charge-localized and bridge-charged states.
• Observed significant variations in the bridge-charged diabatic state and Hamiltonian matrix elements across the dye series.
• Correlated these changes with an inversion of the charge carrier on the bridge, from an electron pair to a hole.

Conclusions:

• The electronic structure of these dyes can be effectively represented by analogous diabatic states.
• Bridge substitution critically influences the electronic properties, particularly the nature of charge carriers.
• Findings provide insights into structure-property relationships for cyanine dye analogues.