From Tetraphenylfurans to Ring-Opened (Z)-1,4-Enediones: ACQ Fluorophores versus AIEgens with Distinct Responses to Mechanical Force and Light.

Two aryl-substituted tetraphenylfurans (TPF-1 and TPF-2) and the corresponding ring-opened (Z)-1,4-enedione derivatives (TPBD-1 and TPBD-2) have been successfully synthesized. Although all the molecules adopt propeller-like configurations, experimental results revealed that the tetraphenylfurans (TPFs) were aggregation-caused quenching (ACQ) fluorophores whereas the 1,4-enediones (TPBDs) were aggregation-induced emission (AIE) active. Additionally, the TPFs and TPBDs exhibited contrasting "turn-on" mechanochromic behavior, with an unusual blueshift of mechanochromic fluorescence for the TPFs and a remarkable redshifted mechanochromism for the TPBDs. Both of these solid-state optical properties were proven to be highly dependent on the mode of molecular packing and substituent effects. In particular, in addition to the tunability of the fluorescent properties through aggregation and mechanical force, ground TPF-1 was found to be efficiently sensitive to light. On the basis of these findings we constructed a smart film with ground TPF-1 and demonstrated its utility in data encryption and decryption well controlled by UV light. Therefore, this work not only provides an insight into the mechanism of AIE as well as mechanochromic effects, but also paves the way towards the development of multifunctional stimuli-responsive materials and devices.