Reversible mechanofluorochromism by simple phenyl and mesitylene appended solid state emitters via crystal to amorphous transitions

Abstract

Developing a variety of organic compounds with bright solid-state emission is highly advantageous, provided they exhibit stimuli-responsive properties. Such ‘smart’ materials offer a remarkable role in sensing, digital machinery, material science, and the biomedical field. Taking this into account, two phenothiazines (PT) appended vinyl-linked aryl unit (mesitylene/phenyl) two based D–π–A structures have been synthesized. The derivatives have exhibited remarkable luminescence characteristics in a diverse set of solvents due to the twisted intramolecular charge transfer (TICT) state and aggregation-induced emission enhancement properties. Surprisingly, between them, only the mesitylene derivative displays significant and highly reversible mechanofluorochromic (MFC) activity by exhibiting an emission shift from sky blue (467 nm) to cyan (482 nm). The mechanistic insight obtained from P-XRD analysis suggests crystal to amorphous transition causes bathochromic shift upon grinding. SEM analysis reveals two discrete morphologies of the MFC compound in its pristine and ground states. Additionally, DFT and TD-DFT calculations provide insight into their electronic energy levels. Furthermore, results from the electrochemical experiment indicate that they are potential candidates for developing optoelectronic devices.