Anh Thy BUI

Univ. Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255, F-33400 Talence, France

Email address: anh-thy.bui@u-bordeaux.fr

In fluorescent organic molecules, a variety of photophysical processes can typically be detrimental to light emission. In this presentation, we will explore how, rather than completely suppressing the population of "dark states", they can be strategically harnessed to achieve functional luminescence.

While triplet states are commonly exploited through phosphorescence, we focus on less conventional processes: triplet-triplet annihilation upconversion (TTA-UC) and thermally activated delayed fluorescence (TADF). For TTA-UC, we push the operational boundaries of this mechanism under sustainably relevant conditions (e.g., using earth-abundant Cu(I) complexes,¹ and/or aqueous solutions) and expand its application scope to include photopolymerization. ² In the case of TADF, we revisit the phenomenon of reverse energy transfer from a lanthanide(III) ion to an organic chromophore. Though typically avoided due to its efficiency in deactivating the metal center, we re-examine this process at a fundamental level. Our work reveals how back-energy transfer can not only be exploited in sensing applications, but also used to uncover novel photophysical behaviors. Through excited-state engineering, we approach the problem from the perspective of the organic dye, uncovering hybrid TADF emission that defies conventional models. This discovery paves the way for original molecules that could address key challenges in TADF materials, with potential implications for next-generation OLEDs.³

In the last part of the presentation, we will highlight the potential of BODIPY derivatives with free torsional movements, often termed “fluorescent molecular rotors”, with a particular focus on molecules that we have engineered to probe low microviscosities. These fluorophores undergo a mechanism involving conical intersections that efficiently deactivate the excited state. However, access to these quenching pathways can be restricted in constrained environments, rendering them particularly effective for studying complex fluid properties in confined systems, such as those encountered in industrial or biological contexts.⁴

References

¹ R Fayad, AT Bui, SG Shepard, FN Castellano*, ACS Appl. Energy Mater. 2020, 3, 12557.

² N Awwad, AT Bui,  EO Danilov, FN Castellano*, Chem 2020, 6, 3071.

³ Emergence@INC 2026 Project “ECLAT”, https://www.inc.cnrs.fr/fr/personne/anh-thy-bui

⁴ M Chi, AT Bui, P Lidon,* Y Medina-Gonzalez*, 2026, in peer review https://doi.org/10.48550/arXiv.2601.15967