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Updated: Sep 19, 2025
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Published on: December 27, 2018
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Aggregation Induced Effects on the Nonradiative Recombination Dynamics of Inverted Singlet-Triplet Heptazine-Based
Laure de Thieulloy1, Robson S Oliboni2, Piotr de Silva1
1Department of Energy Conversion and Storage, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.
The Journal of Physical Chemistry. A
|June 4, 2025
Summary
Heptazine molecules relax quickly, but melem aggregation suppresses this by forming intermolecular charge transfer and preventing ring deformation. This aggregation enhances photoluminescence and offers insights into organic solar cells.
Area of Science:
- Photochemistry
- Materials Science
- Computational Chemistry
Background:
- Heptazine derivatives like melem and melon show potential in photocatalysis and optoelectronics due to thermally activated delayed fluorescence (TADF).
- Insolubility and chemical inertness of these compounds limit understanding of their photorelaxation dynamics.
- Nonradiative pathways significantly influence the photophysical properties of organic optoelectronic materials.
Purpose of the Study:
- To investigate the excited-state nonadiabatic dynamics of heptazine-based molecules and aggregates.
- To elucidate the role of nonradiative decay pathways in the photorelaxation of heptazine derivatives.
- To understand how aggregation affects the photophysical properties of melem.
Main Methods:
- First excited-state nonadiabatic simulations of heptazine and melem molecules and aggregates.
- Analysis of photorelaxation dynamics, including conical intersections and internal conversion.
- Investigating the impact of hydrogen bonding and molecular packing on photophysical processes.
Main Results:
- Isolated heptazine and melem molecules undergo rapid ground-state return (<1 ps) via conical intersections after photoexcitation.
- Melem aggregation significantly suppresses nonradiative photorelaxation.
- Aggregation-induced suppression is attributed to intermolecular charge transfer and restricted molecular deformation, reducing conical intersection formation.
Conclusions:
- Melem aggregation enhances photoluminescence quantum yield through aggregation-induced emission (AIE), beyond its TADF properties.
- Understanding these nonradiative mechanisms is crucial for designing efficient organic solar cells.
- This study provides fundamental insights into the photorelaxation dynamics of heptazine-based materials.
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