Solvatochromism and solution pi-stacking of N-(4-pyridyl)-1,8-naphthalimide and its corresponding triruthenium coordination complex

Author(s)

Mateus, Douglas Braz Goncalves ; Batista, Ana Paula de Lima ; Souza, Samya da Silva ; Demets, Gregoire Jean-Francois ; Nikolaou, Sofia

• Document type: Journal article
• Source: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY; v. 292, p. 7-pg., 2023-02-03.

Abstract

Due to the scarcity of spectroscopic studies on metal-coordinated naphthalimides, and aiming to investigate fundamental spectroscopic aspects, we have described here the aggregates of N-(4-pyridyl)-1,8-naphthalimide (NI-py) in solution as well as solvatochromism displayed by it and by the coordination compounds [Ru3O (CH3COO)(6)(NI-py)(3)](n), n = +1 or 0. Based both on theoretical calculations and luminescence spectra, we demonstrated that in aqueous media, the NI-py pi-stacking is thermodynamically favored, suggesting a preferable conformation where the pyridine and naphthalene moieties of two NI-py molecules are parallel to each other, but are not co-planar within an individual molecule, due to steric hindrance. The NI-py pi pi* band displayed positive solvatochromism, to which the major contribution was the Catalan's SP parameter (solvent polarizability). This observation is fully consistent with the extended pi-electron cloud of the NI-py naphthalene ring. However, a secondary contribution of the SA (solvent acidity) was also observed, owing to the electron pairs available at the N-heteroatom of the pyridine rings and at the carbonyl-group oxygen atoms. Finally, the multiparametric solvent effect analysis indicated that the electronic coupling between coordinated NI-py and the metallic core is modulated by the charge of the [Ru3O(CH3COO)(6)] core, being higher for the reduced species [Ru3O (CH3COO)(6)(NI-py)](0). In addition, in this reduced species, there is no overlap between NI-py pi pi* and the [Ru3O (CH3COO)6] charge transfer (CT) transitions, leading to the observation of the dependence of the CT energy with the SdP parameter (solvent dipolarity) since the CT transition implies in a charge-separation state. (AU)

• FAPESP's process: 18/18060-3 - Use of inorganic supramolecular structures for the development of functional molecules and controlled release of bioactive species
• Grantee: Sofia Nikolaou
• Support Opportunities: Regular Research Grants
• FAPESP's process: 19/04291-6 - Spectroscopic investigation of Ruthenium complexes combined to naphthalimides: solvatochromism, luminescence and pi-stacking
• Grantee: Sâmya da Silva Souza
• Support Opportunities: Scholarships in Brazil - Master