Dimethylamine substituted bisbenzocoumarins: solvatochromic, mechanochromic and acidochromic properties

Abstract

Stimuli-responsive luminescent materials have attracted considerable attention in recent years because of their potential application in various fields. In this work, dimethylamine substituted bisbenzocoumarin (DB-Cn) derivatives are synthesized and their optical properties are investigated. These molecules show solvatochromic and mechanochromic properties. Powder wide-angle X-ray diffraction and differential scanning calorimetry curves reveal that the initial crystalline states are transformed to amorphous states under various external stimuli. Single crystal X-ray analysis of DB-C2 reveals that the destruction of the crystal conformation and the changes of intermolecular π–π stacking interactions could be responsible for the red-shifted emission. Further investigation revealed that DB-C2 showed acidochromic properties and could be utilized as a security ink. The control ¹H NMR experiment reveals that the protonation of the aromatic amines is essential for the acidochromic properties. This work provides information on the mechanism study of stimuli-responsive luminescence properties of binaphthalene-type luminescent materials and expands the potential application of these materials.