Figure 1.

General structure of a molecular rotor (A), highlighting the electron donating subunit (green), the electron accepting subunit (red), and the spacer unit (blue), which spatially separates the donor and acceptor groups. Typical representatives are aniline nitriles, such as 1,4-dimethylamino benzonitrile (DMABN, B), julolidine malononitriles, such as 9-(dicyanovinyl) julolidine (DCVJ, C), and stilbenes, such as p-(dimethylamino) stilbazolium (p-DASPMI, D). The arrows indicate bonds around which intramolecular rotation can take place.