Aggregation-induced and stimuli-responsive emission modulation in pyridyl-imidazole compounds connected to naphthalene, anthracene and pyrene motifs for the design of sensors and switches

Abstract

A new category of pyridyl-imidazole-based compounds connected to naphthalene, anthracene and pyrene motifs is synthesized and thoroughly characterized. A detailed investigation of their photophysical properties is conducted in a wide range of solvents. They display both aggregation-caused quenching (ACQ) and aggregation-induced enhanced emission (AIEE) in appropriate solvent and non-solvent mixtures, as evidenced by a shift in the emission maximum and the outcomes of dynamic light scattering (DLS) and scanning electron microscopic (SEM) measurements. Acid-, anion- and temperature-induced modulation of the spectral properties of the compounds are thoroughly explored via multiple optical tools and spectroscopic techniques. The compounds function as selective sensors for anions (F⁻ and CN⁻). Interestingly, the compounds also act as deep blue and single component white light emitters under the cumulative influence of specific solvents and temperatures. Computational studies involving density functional theory (DFT) and time-dependent (TD)-DFT are also performed to visualize the electronic structures of the compounds and assign the spectral bands appropriately.