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Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional π-conjugate Systems

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Excited-State Absorption Drives Low-Energy Optical Limiting in Oligothiophenes.

Mustapha Driouech^1,2, Michele Guerrini², Caterina Cocchi^1,2,3

¹Friedrich-Schiller Universität Jena, Institute for Condensed Matter Theory and Optics, 07743 Jena, Germany.

The Journal of Physical Chemistry Letters

|November 6, 2025

Summary

This study reveals excited-state absorption (ESA) as the key mechanism for optical limiting (OL) in thiophene oligomers. Understanding ESA in these organic semiconductors is crucial for developing advanced materials for radiation protection.

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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

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Published on: May 27, 2020

Area of Science:

Materials Science
Quantum Chemistry
Optics

Background:

Optical limiting (OL) protects against intense radiation by managing nonlinear optical properties.
Understanding nonlinear optical responses is vital for material design.
Thiophene oligomers are key components in organic semiconductors.

Purpose of the Study:

Investigate the optical limiting mechanisms in thiophene oligomers.
Determine the role of excited-state absorption (ESA) in OL.
Provide insights for designing novel organic semiconductors with enhanced nonlinear optical characteristics.

Main Methods:

Utilized ab initio real-time time-dependent density-functional theory (TD-DFT).
Analyzed absorption spectra under intense broadband radiation.
Studied population dynamics by exciting oligothiophenes to specific excited states.

Main Results:

Observed significant growth in absorption cross-section below linear excitation onset under strong fields, indicating OL.
Identified excited-state absorption (ESA) in the near-infrared to visible spectrum.
Confirmed ESA as the primary mechanism driving optical limiting in these molecules.

Conclusions:

Excited-state absorption (ESA) is the dominant mechanism for optical limiting in oligothiophene-based organic semiconductors.
This research offers crucial insights for the rational design of materials with tailored nonlinear optical properties for radiation protection applications.