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

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 π-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 ππ* 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 π-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 ππ* 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.

Enhanced Li+ charge storage in naphthalene diimide/vanadium pentoxide intercalates.

N,N'-Bis(4-aminophenyl)-1,4,5,8-naphthalene diimide (NDI-ph) was intercalated into lamellar vanadium pentoxide (V2O5) in different amounts to prepare hybrid intercalates. The presence of the imide supports the material's ability to form lithium salts with the structural stabilization of the oxide matrix. This effect is remarkable in charge/discharge cycles in terms of Li+ uptake and discharge by the lamellar intercalates, as we could double the ion uptake capacity (1.27 Li+ per V2O5 unit vs. 0.66 for pure V2O5), enhance the chemical reversibility and double the specific charge capacity (188 mA h g-1 vs. 98 mA h g-1 for pure V2O5) with very small amounts of this imide. This is the first paper dealing with naphthalene diimide intercalates in vanadium pentoxide xerogel for Li+ storage.