Abstract: Molecular machines are molecules that can perform mechanical movement like motion upon stimulation. The central carbon-carbon double bond in the light-driven molecular motors based on overcrowded alkenes can undergo photochemical isomerization upon irradiation by certain wavelength light, which is followed by a thermal step to control the unidirectionality of the rotation. The unidirectional rotation is the most important feature that distinguishes this type of motor from other photo-responsive switches. This review introduces the functional synthesis of the motors and describes their application in controlled molecular motion, dynamic self-assembled system and smart materials.