Schiff Base-bridged TPE-Rhodamine Dyad: Facile Synthesis, Distinct Response to Shearing and Hydrostatic Pressure, Sequential Multicolored Acidichromism

In this article, we report a newly designed TPE-rhodamine dyad bridged by Schiff base structure, which can be synthesized facilely and achieves AIEE, distinct response to shearing and hydrostatic pressure and intriguing sequential multicolored acidichromism, owing to the imine group and spiro-lactam structure. RhB=TPE displayed AIEE property in THF/H2O system, due to water-induced aggregation and aggregation-suppressed nonradiative relaxation ways of the excited states. The single crystal of RhB=TPE was obtained and the complex intermolecular interactions were analyzed. RhB=TPE showed distinct response to anisotropic shearing force and isotropic hydrostatic pressure. By shearing, the crystal powder underwent the emission color switch from blue (440 nm) to green (475 nm) and further to reddish (580 nm), which were ascribed to the LE emission, HLCT emission and ring-open species of rhodamine lactam respectively. When subjected to hydrostatic pressure, the single crystal displayed color change from blue to green and to dark, because of the pressure-induced separation of HLCT and further emission quenching. More interestingly, RhB=TPE realized high-contrast sequential color switch from blue to yellow and further to reddish by fuming with TFA. The protonation of imine and rhodamine played the key role in the multicolored change. To the best of our knowledge, RhB=TPE is a rare dyad that achieves sequential multicolored switch by external force and acid, respectively. This study may contribute to develop multistimuli-responsive fluorescent switch with multicolored change.