Design and synthesis of phenothiazine functionalized mechanochromic materials

Abstract

The phenomena in which a fluorescent compound changes its fluorescence colour in response to an external mechanical force such as scratching, grinding, rubbing, or shearing is called as mechanochromism. The mechanochromically active compounds are frequently used in a variety of optoelectronic devices such as light emitting diodes (LEDs), non-linear optics (NLO), pressure and strain sensors, deformation detectors, data storage devices and fluorescent tags. A compound must have intense emission in the solid state in order to exhibit mechanochromism. Most of the conventional fluorophores such as quinine sulphate, fluorescein, rhodamine and perylene show strong emission in the solution state but are non-emissive in the solid state. This is due to the enhanced π-π stacking interactions in the solid state which favours non-radiative decay channels for the dissipation of excited state energy. The solid state emission of such fluorophores could be improved by the aggregation induced emission (AIE) mechanism, in which the employment of several non-planar moieties containing rotatable aromatic rings allows the non-emissive materials to become emissive when aggregated. The introduction of AIE active luminogens in conventional organic fluorophores that are usually non-emissive in the solid-state has proved to be a promising technique for furnishing materials with efficient emission in the solid state.