Piezochromic Carbon Dots with Two‐photon Fluorescence

Piezochromic materials, which show color changes resulting from mechanical grinding or external pressure, can be used as mechanosensors, indicators of mechano‐history, security papers, optoelectronic devices, and data storage systems. A class of piezochromic materials with unprecedented two‐photon absorptive and yellow emissive carbon dots (CDs) was developed for the first time. Applied pressure from 0–22.84 GPa caused a noticeable color change in the luminescence of yellow emissive CDs, shifting from yellow (557 nm) to blue‐green (491 nm). Moreover, first‐principles calculations support transformation of the sp 2 domains into sp 3 ‐hybridized domains under high pressure. The structured CDs generated were captured by quenching the high‐pressure phase to ambient conditions, thus greatly increasing the choice of materials available for a variety of applications.