Fluorosolvatochromic Behavior of 2,3-Naphthalimides Expanded by Double Fusion with Benzothiophene and Benzofuran Units

摘要

As new polycyclic aromatic hydrocarbons (PAHs) containing an imide group, we designed and synthesized 2,3-naphthalimide fused with benzothiophene 1 or benzofuran 2. 1 and 2 have a push-pull structure attributed to the imide group and the electron-donating heterocyclic moieties, indicated that 1 and 2 play as a fluorosolvatochromic dye. 1 and 2 were synthesized in 3-steps. The absorption and fluorescence spectra were measured in twelve different solvents. The absorption spectra of 1 and 2 showed a slight solvent dependence. On the other hand, a strong solvent dependence was observed in the fluorescence spectra of 1 and 2, that is, fluorosolvatochromism. The plots of the emission maximum versus the solvent polarity parameter ET(30) for 1 and 2 exhibited a good linear correlation. Multiple linear regression analysis using Catalan scale suggested that the fluorescence behavior of 1 and 2 is influenced by the acidity and dipolarity of the solvents. The changes in the dipole moment between the ground and excited states estimated by the Lippert-Mataga equation were 7.6 D for 1 and 7.2 D for 2.