High-contrast luminescence dependent on polymorphism and mechanochromism of AIE-active (4-(phenothiazin-10-yl)phenyl)(pyren-1-yl)methanone

Robust mechanochromic luminescent materials are highly in demand for high-tech applications, such as mechanosensors and data recording. In this work, a new luminogen (4-(phenothiazin-10-yl)phenyl)(pyren-1-yl)methanone (Py-BP-PTZ) is synthesized and characterized, and its crystal structure and photophysical properties are investigated. Py-BP-PTZ exhibits apparent aggregation-induced emission, and polymorphism and mechanochromism properties. Two kinds of crystals with sky blue (463 nm) and green (557 nm) photoluminescence (PL), respectively, are obtained. And the sky blue PL is progressively red-shifted to orange PL (592 nm) along with the PL intensity change when the crystal is compressed under gradually strengthened external pressure. When the external pressure is released, the original sky blue PL and a new PL peak (582 nm) are recorded. Similar mechanochromic luminescence behaviors under altered external pressures are also found for the pristine solid of Py-BP-PTZ, with the PL change between sky blue (463 nm) and orange red (627 nm). In addition, the solid of Py-BP-PTZ shows reversible PL changes between sky blue (463 nm) and yellow (556 nm) by repeated grinding and solvent fuming. These interesting mechanochromic luminescence behaviors are rationalized to be caused by the changes in molecular conformations, intermolecular interactions, molecular packing patterns and aggregate morphologies. This new mechanochromic luminogen and understanding of the relevant mechanism should be useful for further development and application of new mechanochromic luminescent materials.