Temperature-Dependent Mechanochromic Behavior of Mechanoresponsive Luminescent Compounds

Mechanoresponsive luminescent (MRL) compounds change their emission color upon mechanical treatment. Hundreds of MRL compounds have been studied, but their mechanically triggered response at elevated temperature has remained virtually unexplored. Here, we demonstrate that the temperature can have a significant influence on the mechanically induced response of MRL compounds. The photoluminescence of a new cyano-substituted oligo(p-phenylenevinylene) derivative was shown to exhibit a significant red-shift when ground at ambient temperature, whereas the same treatment at 100 °C leads to a hypsochromic shift. The behavior at ambient is caused by a mechanically induced phase transition from a crystalline to an amorphous solid in which the dye molecules form excimers, whereas at elevated temperature the hypsochromic shift is ascribed to a crystalline–crystalline phase transition. Such temperature-dependent MRL behavior was not previously observed, but it appears to be a general effect that is useful for sophisticated mechano-sensing materials and devices.