Figure 3.

Examples for different force responses of OFPs undergoing non‐scissile covalent bond isomerization, non‐covalent bond rearrangement, or bond rotation. (a) Schematic depiction and (b) structural formula of exemplary OFPs. Spiropyran is a non‐scissile, reversible OFP that undergoes covalent bond isomerization to merocyanine, which has purple color and is red fluorescent. ^[31] PBI loops vary between excimer (associated) and monomer (dissociated) emission. ^[38] Diketopyrrolopyrroles change the emission wavelength based on charge transfer from the planarization of the twisted phenyl moiety. ^[45]