Resonant Raman spectra of diindenoperylene thin films

Area of Science:

• Physical Chemistry
• Spectroscopy
• Materials Science

Background:

• Diindenoperylene (DIP) is a polycyclic aromatic hydrocarbon with potential applications in organic electronics.
• Understanding the excited-state properties of DIP is crucial for optimizing its performance in devices.
• Raman spectroscopy is a powerful tool for probing molecular vibrations and electronic structures.

Purpose of the Study:

• To interpret resonant and preresonant Raman spectra of diindenoperylene (DIP) thin films.
• To determine the most reliable method for calculating excited-state geometries of DIP.
• To assign observed Raman peaks and analyze Raman excitation profiles.

Main Methods:

• Density Functional Theory (DFT) calculations, including time-dependent DFT and constrained DFT.
• Analysis of resonant and preresonant Raman spectra of DIP thin films.
• Comparison of calculated excited-state geometries with experimental absorption spectra.
• Raman excitation profile analysis considering the frequency dependence of the dielectric tensor.

Main Results:

• Constrained DFT calculations provide a more reliable deformation pattern for excited DIP molecules compared to time-dependent DFT.
• Most observed Raman peaks were assigned to calculated A(g)-symmetric breathing modes and their combinations.
• Raman cross sections derived from excitation profile analysis showed good agreement with observed relative intensities in both resonant and preresonant cases.

Conclusions:

• Constrained DFT is a suitable method for predicting excited-state geometries of DIP relevant to its Raman spectra.
• The study successfully assigns Raman spectral features to specific molecular vibrations of DIP.
• The findings contribute to a deeper understanding of the photophysical properties of DIP for potential applications.