Fluorescent molecular force probes have been developed for rheology and mechanobiology. Single covalent bond is generally cleaved by nano-Newton force, which has been confirmed by the analyses of AFM and optical tweezers. To quantitatively evaluate stress concentration in stretched polymeric materials or biological systems before they break, pico- Newton force must be detected at molecular scale, and therefore molecular force probes based on a bond-breaking mechanism cannot be used for this purpose. Here we have explored flexible force probes that show fluorescence response by a conformational change of flapping π-conjugated molecules (FLAP), which have the potential to realize fluorescence response to pico-Newton forces. In this presentation, a series of FLAPs synthesized in our laboratory will be introduced in connection with the force mapping technology.
Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of the following essential requisites: (i) adequate strength for a temporary bond (more than 1 MPa) even under heating conditions, (ii) significant reduction of the bonding strengths by light irradiation, and (iii) quick photoresponse for the separation of bonded materials. Here we present a liquid crystal (LC) material that satisfies all of the above-mentioned requisites for the light-melt adhesives, namely, (i) a shear strength over 1 MPa up to 110 °C for bonding glass plates, (ii) an 85% reduction of the strength by ultraviolet (UV) irradiation, and (iii) an instant photomelting of the LC film in a few seconds. Moreover, this material is reusable as an adhesive, and the transformation between the LC and melted phases is associated with an informative color change in fluorescence. We envision that composite materials with the light-melt function will further improve the performance in manufacturing processes, which will accelerate the on-demand photoseparation technology complementary to the other switchable adhesion approaches.