Two-dimensional electronic-vibrational spectra: modeling correlated electronic and nuclear motion
1Dipartimento di Chimica, Università di Parma & INSTM UdR Parma, Parco Area delle Scienze 17/a, 43124 Parma, Italy. francesca.terenziani@unipr.it.
Physical Chemistry Chemical Physics : PCCP
|April 28, 2015
Summary
We calculated 2D electronic-vibrational (2D-EV) spectra for organic dyes, revealing that DCM dye uses a simple two-state model, while AAC dye requires a three-state model for accurate spectral representation.
Area of Science:
- Computational chemistry
- Spectroscopy
- Physical chemistry
Background:
- Understanding the electronic and vibrational properties of organic dyes is crucial for their application in various fields.
- Solvation effects significantly influence the spectroscopic behavior of dyes.
- Distinguishing between locally-excited (LE) and charge-transfer (CT) states is essential for interpreting dye photophysics.
Purpose of the Study:
- To calculate and analyze 2D electronic-vibrational (2D-EV) spectra of solvated organic dyes.
- To model the spectroscopic behavior of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and 8-(N,N-dibutylamino)-2-azachrysene (AAC).
- To resolve the long-standing debate regarding the nature of low-lying excitations in DCM.
Main Methods:
- Utilizing a reduced set of electronic diabatic states (essential states) coupled to molecular vibrations.
- Employing an effective overdamped coordinate governed by the Smoluchowski diffusion equation to simulate polar solvation.
- Calculating 2D-EV spectra and comparing them with linear absorption, fluorescence spectra, and experimental data.
Main Results:
- A minimal two-state model accurately reproduces the linear absorption and fluorescence spectra of DCM.
- The calculated 2D-EV spectra for DCM align well with recent experimental findings.
- Linear spectra of AAC indicate a complex interplay between LE and CT excitations, necessitating a three-state model.
- Calculated 2D-EV spectra for AAC exhibit distinct behavior compared to DCM, refuting a LE/CT interplay for DCM.
Conclusions:
- The simplest two-state model is sufficient to describe the spectroscopic properties of DCM.
- The experimental data for DCM do not support a LE/CT excitation interplay.
- A three-state model is required to accurately describe the spectroscopic behavior of AAC.
- This study clarifies the nature of low-lying excitations in DCM, favoring a straightforward interpretation.
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