In addition to theoretical investigations, researchers have also employed more rational molecular design strategies to verify the correlation between the rotation of the central double bond and AIE properties. Zheng and coworkers adopted a distinct approach to immobilize the benzene ring rotator and synthesized cis and gem TPE derivatives (Figure ). The two neighboring pairs of phenyl rings were constrained from rotation, yet the bridging moiety, aligned parallel to the central olefin double bond, emitted light in solution, while the TPE derivative with the bridging moiety perpendicular to the double bond still exhibited AIE properties. In addition, they posit that this phenomenon arises from the disruption of conjugation in the sp 2 electronic structure of the two carbon atoms forming the central double bond, leading to the creation of a rotatable single bond in the excited state (Figure ). (c) The distinct AIE behavior of TPE derivatives in cis and gem configurations is attributed to the inherent mechanism, where the central conjugated double bond in the gem configuration opens to form a rotor structure in solution. Reproduced from Ref. with permission. Copyright (2018), American Chemical Society.