Spontaneous Self-Assembly of a 1,8-Naphthyridine into Diverse Crystalline 1D Nanostructures: Implications on the Stimuli-Responsive Luminescent Behaviour

The previously reported organic solid-state fluorophore 7-(3,4-dimethoxyphenyl)-2-ethoxy-4-phenyl-1,8-naphthyridine-3-carbonitrile 1 was found to spontaneously self-organize into diverse 1D crystalline nanostructures by choosing appropriate liquid phase self-assembly conditions. Experimental results, as well as DFT quantum calculations (at the M06-2X/6-31+G(d) level), shed light on the aggregation mechanism. This was found in good agreement with molecules being primarily joined together through intermolecular alignment caused by electrostatic interactions, as well as minimization of the steric repulsions. This alignment provokes the preferential growth of the crystalline materials into 1D aggregates, as well as the observed fluorescence of the material in the solid state. Luminescent nanowires, nanodendrons, and nanodendrimers, obtained following this spontaneous liquid phase self-assembly, have shown a versatile fluorescent behavior. Here, the obtained nanostructured materials showed a blue-shifted emission compared to the previously reported polycrystalline or single crystalline samples of 1 (Pbca), together with thermo- and acido-fluorochromism, plus piezochromic aggregation-induced emission.