A [3]rotaxane with two [2]rotaxane arms bridged by an overcrowded alkene switch has been constructed to perform the clamlike motion in response to light stimulus. We demonstrated that this [3]rotaxane can undergo reversible conformational changes caused by the trans-cis isomerizations of the central double bond with a favorable photostationary state (up to 90% conversion). It has been shown that the clamlike motion causes remarkable UV-vis and fluorescence spectral changes, allowing it to behave as a reversible optical molecular switch.