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Peer-reviewedCC BY-NC 3.0Chemical Science

Simulated transient absorption reveals torsion-dependent nonradiative relaxation in a near-infrared nanographene emitter

  • Royle Perez-Castillo1
  • Victor M. Freixas2
  • Hassiel Negrin-Yuvero1
  • Maxim F. Gelin3
  • Giuseppe M. Paternò4,5
  • Guglielmo Lanzani4
  • Sergei Tretiak6
  • Sebastian Fernandez-Alberti1
6 affiliations
  1. 1Departamento de Ciencia y Tecnologia, Universidad Nacional de Quilmes/CONICET B1876BXD Bernal Argentina
  2. 2Department of Chemistry and Physics and Astronomy, University of California Irvine California 92697-2025 USA
  3. 3School of Sciences, Hangzhou Dianzi University Hangzhou 310018 China
  4. 4Center for Nano Science and Technology, Istituto Italiano di Tecnologia (IIT) Via Rubattino 81 20134 Milano Italy
  5. 5Physics Department, Politecnico di Milano Piazza L. da Vinci 32 Milano 20133 Italy
  6. 6Theoretical Division, Center for Nonlinear Studies (CNLS), Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory Los Alamos NM 87545 USA
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Abstract

Functionalized nanographenes are emerging near-infrared emitters, yet the microscopic pathways underlying their ultrafast excited-state dynamics remain elusive. Here, we combine atomistic nonadiabatic simulations with transient absorption (TA) modeling to analyze the relaxation mechanisms in a donor–acceptor nanographene. We find that, during the decay of the initially populated higher-lying excited states, the transition density redistributes from the substituents to the nanographene core. This early process occurs in both fully flexible and dihedral-constrained trajectories. In contrast, relaxation into the lowest excited state is strongly torsion-dependent: freezing the donor–acceptor dihedral suppresses this nonadiabatic decay and traps population in higher-lying excited states. Decomposition of the TA signal into ground-state bleaching, stimulated emission, and excited-state absorption elucidates that access to the lowest excited state correlates with the buildup of stimulated emission in the near-infrared, while excited-state absorption remains weak in this spectral window. These results disentangle early electronic relaxation from torsion-assisted interstate decay and clarify how structural dynamics shape the spectroscopic signatures associated with efficient near-infrared emission in functionalized nanographenes. These insights provide molecular-level design principles for controlling excited-state relaxation and enhancing optical gain in near-infrared emitters.

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Cite

BibTeXRIS
BibTeX
@article{perezcastillo2026simulated,
  title = {{Simulated transient absorption reveals torsion-dependent nonradiative relaxation in a near-infrared nanographene emitter}},
  author = {Royle Perez-Castillo and Victor M. Freixas and Hassiel Negrin-Yuvero and Maxim F. Gelin and Giuseppe M. Paternò and Guglielmo Lanzani and Sergei Tretiak and Sebastian Fernandez-Alberti},
  journal = {Chemical Science},
  year = {2026},
  month = aug,
  doi = {10.1039/d6sc04459j},
  url = {https://doi.org/10.1039/d6sc04459j},
  note = {CC BY-NC 3.0},
}
RIS
TY  - JOUR
TI  - Simulated transient absorption reveals torsion-dependent nonradiative relaxation in a near-infrared nanographene emitter
AU  - Royle Perez-Castillo
AU  - Victor M. Freixas
AU  - Hassiel Negrin-Yuvero
AU  - Maxim F. Gelin
AU  - Giuseppe M. Paternò
AU  - Guglielmo Lanzani
AU  - Sergei Tretiak
AU  - Sebastian Fernandez-Alberti
PY  - 2026
DA  - 2026/08/27
JO  - Chemical Science
DO  - 10.1039/d6sc04459j
UR  - https://doi.org/10.1039/d6sc04459j
AB  - Functionalized nanographenes are emerging near-infrared emitters, yet the microscopic pathways underlying their ultrafast excited-state dynamics remain elusive. Here, we combine atomistic nonadiabatic simulations with transient absorption (TA) modeling to analyze the relaxation mechanisms in a donor–acceptor nanographene. We find that, during the decay of the initially populated higher-lying excited states, the transition density redistributes from the substituents to the nanographene core. This early process occurs in both fully flexible and dihedral-constrained trajectories. In contrast, relaxation into the lowest excited state is strongly torsion-dependent: freezing the donor–acceptor dihedral suppresses this nonadiabatic decay and traps population in higher-lying excited states. Decomposition of the TA signal into ground-state bleaching, stimulated emission, and excited-state absorption elucidates that access to the lowest excited state correlates with the buildup of stimulated emission in the near-infrared, while excited-state absorption remains weak in this spectral window. These results disentangle early electronic relaxation from torsion-assisted interstate decay and clarify how structural dynamics shape the spectroscopic signatures associated with efficient near-infrared emission in functionalized nanographenes. These insights provide molecular-level design principles for controlling excited-state relaxation and enhancing optical gain in near-infrared emitters.
SN  - 2041-6520
SN  - 2041-6539
ER  -