ABSTRACT
This chapter introduces flapping molecules and their versatile functions, whose structure is composed of rigid aromatic wings and a conformationally flexible joint. Photophysical properties and molecular assembly modes can be tailored in a series of the flapping systems. The chapter describes the applications particularly as a viscosity probe and a light-melt adhesive. Conformational rigidity plays an important role in the molecular chemistry and materials science of π-conjugated systems. The inherent rigidity of p-skeletons means the difficulty in providing convertible photophysical properties, which would originate from the flexibility of molecular structures. Although conformational flexibility would be the key to create dynamic functions, not every flexible p-molecule displays convertible photophysical properties. Viscosity mapping by synthetic fluorescent probes is a useful technique because it can visualize local viscosity distribution in heterogeneous media. Photoinduced phase transition has been well studied on materials containing isomerization dyes such as azobenzene, diarylethene and spiropyran.
