Ratiometric Piezochromism of Electrospun Polymer Films: Intermolecular Interactions for Enhanced Sensitivity and Color Difference.

Many piezochromic luminescent (PCL) dyes are known for their fluorescent switching capacity in the powdered phase, but they are usually difficult to utilize practically owing to poor mechanical properties. Herein, a nanofiber film fabricated through an electrospinning process is doped with PCL dye. The electrospun film not only reveals the mechanics of macromolecular materials, but also achieves precise, gradient pressure recognition (ratiometric PCL behavior). The PCL sensitivity and color difference of the dye in a crystalline state are calculated to be 15.7 nm GPa-1 and 149 nm, respectively. The sensitivity of an electrospun film containing 0.1 % (w/w) dye decreased to 3.6 nm GPa-1 . Moreover, the individual effects of molecular conformation and intermolecular interaction on the PCL properties have been clearly distinguished through in situ high-pressure experiments. Intermolecular interactions play a more significant role in PCL color difference and sensitivity. The film fabricated through an electrospinning process contributes to understanding of the working mechanism and real applications of piezochromic materials.

Highly Twisted Isomers of Triphenylacrylonitrile Derivatives with High Emission Efficiency and Mechanochromic Behavior.

Two novel triphenylacrylonitrile derivatives (TPAN-C2 and TPAN-C3) with highly twisted conformations have been successfully prepared by Suzuki coupling reaction. Both of them show mechanochromic (MC) fluorescent behaviour and exhibit remarkable fluorescence redshifts from sky-blue to light green upon fully grinding them. Interestingly, the ground powders recover their original states upon heating at 100 °C for 1 min or fuming with solvents vapour. Such intriguing MC properties of TPAN-C2 and TPAN-C3 are attributed to their phase transitions between crystalline and amorphous states, which are confirmed by powder X-ray diffraction (XRD) data. Moreover, the behaviour of both TPAN-C2 and TPAN-C3 indicates that the aggregation-induced emission (AIE) gives rise to rather high fluorescence quantum efficiencies (Φf ) of 0.78 and 0.97, respectively. The influences of stacking mode and molecular conformation on MC properties and the high Φf of TPAN-C2 and TPAN-C3 are discussed.