Supramolecular aggregation properties of naphthalimide-decorated imino-Naphthol and imino-naphthalene based on fluorescent materials

Abstract

Two kinds of 1,8-naphthalimide derivatives 18 and 18OH were synthesized and their properties were explored in solution, gel and crystal. The 18 and 18OH exhibited different emission properties in different solvents. With the solvent change from non-polar toluene to polar DMSO, the emission colors were transformed from green to yellow or red. Both compounds could form gels in the certain solvent. Particularly, the xerogels of 18 were observed to form sheet, fiber and spherical microstructures in different solvents by scanning electron microscopy (SEM). More interestingly, 18OH showed rare five typical solvatochromic properties in the presence of multiple acted groups, and produced a tunable fluorescence between 572 and 624 nm (Φf =1.4 to 39.8%). According to the single crystal structural analysis, the supra-molecular interactions (π···π, H-bonding, and CH···π) observed in the five crystal rigidified the fluorophores and enhanced the solid-state fluorescence. To further figure out how the solvent influenced the intermolecular interaction, the density functional theory (DFT) calculations were utilized to explore the electronic and structural properties of these solvatochromic transformations in ground and excited state. Furthermore, The xerogels of the two compounds had the reversible mechanofluorochromic (MFC) behavior. Through grinding and fuming, the fluorescence of xerogels could be reversibly changed between yellow and orange. Lastly, the gels of two compounds could be regenerated by different responsive behaviors under the circulating stimulation of TEA and TFA.