Elastic organic crystals of π-conjugated molecules: anisotropic densely packed supramolecular 3D polymers exhibit mechanical flexibility and shape tunability

π-Conjugated molecules have attracted much attention over recent years and have applications in various organic devices. Single crystals of these molecules are attractive materials for developing unique and/or high-performance devices owing to their anisotropic densely packed supramolecular 3D polymer structures. However, they are not flexible and are therefore not suitable for wearable devices. In this focus review, the author’s recent work on flexible crystals involving designing fibril lamella of slip-stacked molecular wires based on planar π-conjugated molecules and their applications is summarized. Unlike common organic crystals, 1,4-bis[2-(4-methylthienyl)]-2,3,5,6-tetrafluorobenzene exhibits elastic bending flexibility with π-functionality. This supramolecular 3D polymer design concept offers top–down synthesis of crystalline fibers and films. Moreover, the functionality and flexibility of such a crystal realizes both high-performance flexible fluorescent waveguide and reversible mechanofluorochromic behavior. Finally, the interesting shape-tunable supramolecular formation of a fluorescent π-conjugated polymer containing a 1,4-bis[2-(4-hexylthienyl)]-2,3,5,6-tetrafluorobenzene repeating unit is described