Optical Absorption by Charge-Transfer Molecules.

Area of Science:

• Theoretical Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Charge-transfer (CT) molecules are crucial in various chemical and biological processes.
• Accurate theoretical models are needed to understand radiation absorption by CT molecules, especially those with delocalized electronic density.
• Existing models often struggle to consistently incorporate vibronic coupling and medium polarization effects.

Purpose of the Study:

• To develop a novel analytical formalism for calculating radiation absorption in charge-transfer molecules.
• To consistently incorporate vibronic coupling to quantum intramolecular vibrations and electrostatic interactions with a polarizable medium.
• To provide a theoretical framework applicable to both localized diabatic and delocalized adiabatic electronic states.

Main Methods:

• Development of a basis-invariant analytical formalism for radiation absorption calculations.
• Consistent incorporation of vibronic coupling and polarizable medium interactions.
• Derivation of analytical formulas for CT absorption bands and spectral moments.

Main Results:

• A new definition for the Huang-Rhys factor is introduced to account for electronic delocalization.
• Basis-invariant reorganization energy is identified as key for observable spectroscopic parameters.
• Analytical formulas connect molecular properties to spectroscopic observables like absorption bands and spectral moments.

Conclusions:

• The developed theory provides a robust framework for understanding and predicting radiation absorption in charge-transfer molecules.
• The formalism accurately describes the influence of electronic delocalization and environmental interactions on spectroscopic properties.
• The theory's validity is demonstrated through successful application to experimental data for optical absorption and emission transitions.