Multi-Stimuli Responsive Donor-Acceptor Tetraphenylethylene Substituted Benzothiadiazoles

Abstract

In order to understand how the donor (D)/acceptor (A) substituents and their substitution pattern affect the solution and solid-state optical properties, a series of symmetrical and unsymmetrical TPE substituted BTDs 3-8 were designed and synthesized by the Suzuki and Stille coupling reactions. Their solvatochromic, aggregation induced emission (AIE), mechanochromic, and vapochromic properties were studied and compared. The single-crystal X-ray structures of BTDs 5 and 6 are reported. The BTDs 3-8 are highly fluorescent with the tunable emissions. The solvent dependent emission was observed in BTDs 3-8 and their Lippert-Mataga plots show a linear correlation of the Stokes shift with solvent polarity. The emission study in different tetrahydrofuran (THF):water percentages show enhanced emission in aggregates. The BTDs exhibit a reversible multi-stimuli response toward mechanical force, solvent, and heat. The detailed study using single-crystal X-ray, photophysical properties, powder X-ray diffraction, scanning electron microscopy, and theoretical calculation reveals that the planarization induced enhancement in conjugation and conversion of crystalline to amorphous state are responsible for mechanochromism and vapochromism. Our work has elucidated that this general approach can be utilized to develop a promising class of multi-stimuli responsive materials. © 2016 American Chemical Society.