Aggregation Suppresses Internal Conversion and Enhances Triplet Yield in π-Rich Natural Dyes by Vibronic Coupling Control: A Case Study of Hypericin Supramolecular Assembly
Year: 2025
Type: article
Abstract: Hypericin, a naturally occurring anthraquinone dye, displays unusually high triplet quantum yields despite its weak spin–orbit coupling and strong propensity to aggregate in solution—an apparent contradiction to conventional photophysical models. Using quantum chemical calculations and long-timescale molecular dynamics simulations, we show that supramolecular aggregation, particularly dimer formation, profoundly alters excited-state dynamics. Aggregation suppresses internal conversion by reducing nonadiabatic coupling and damping low-frequency vibrational modes, thereby prolonging excited-state lifetimes. Concurrently, excitonic interactions and energetic reordering of excited states increase the density of accessible triplet levels, enabling efficient intersystem crossing through energetically favorable pathways—even in the absence of enhanced spin–orbit coupling. These findings reconcile previously unexplained discrepancies between theoretical predictions and experimental observations for hypericin, and provide a broadly applicable mechanistic framework for enhancing triplet generation in heavy-atom-free photosensitizers through supramolecular design.
Source: Journal of Natural Products
Author: Maciej Spiegel
Institution: Wroclaw Medical University
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4417439508