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arXiv · 2412.18638

Luminescent Trityl-based Diradicaloids: A Theoretical and Experimental Assessment of Charge-Resonance in Low-Lying Excited States

Davide Mesto·Michele Orza·Brunella Bardi·Angela Punzi·Imma Ratera·Jaume Veciana·Gianluca Farinola·Anna Painelli·Francesca Terenziani·Davide Blasi·Fabrizia Negri
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Abstract

The tris(2,4,6-trichlorophenyl)methyl radical (TTM) has inspired the synthesis of several luminescent diradicals and diradicaloids, providing an extraordinary opportunity to control the nature of the low-lying excited states by fine-tuning the diradical character. However, the photophysical properties of TTM-derived diradicals remain not fully understood yet. Here we present a combined theoretical and experimental investigation on TTM-derived diradicals to elucidate the origin of their luminescence. The theoretical analysis focuses on a series of symmetric TTM-derived diradicals with singlet ground state, featuring radical moieties linked by pi-conjugated spacers of different length. The nature of the lowest excited electronic states that control their photophysical behaviour is discussed in detail. The study is complemented by a complete spectroscopic characterization of the TTM-TTM diradical, synthesized using a novel, simpler and more efficient procedure exploiting the unique reactivity of TTM. The lowest excited states of the diradicals differ qualitatively from those of TTM: two novel low-lying states emerge in the diradical, due to charge resonance (CR) between the two radical units. The lowest CR state is a dark state for symmetric diradicals. The CR nature explains the blue-shifted emission observed by increasing the distance between the radical centres as seen in TTM-ph-TTM. This insight suggests different design strategies to improve the luminescence properties of TTM-derived diradicals

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Davide Mesto, Michele Orza, Brunella Bardi, Angela Punzi, Imma Ratera, Jaume Veciana, Gianluca Farinola, Anna Painelli, Francesca Terenziani, Davide Blasi, Fabrizia Negri. 2025-01-04. Luminescent Trityl-based Diradicaloids: A Theoretical and Experimental Assessment of Charge-Resonance in Low-Lying Excited States. https://doi.org/10.1002/chem.202500749

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