Bound on the time variation of the fine structure constant driven by quintessence

The bound on the time variation of the fine structure constant (α) driven by the dynamics of quintessence scalar field which is coupled to electromagnetism is discussed using phenomenological quintessential models constrained by SNIa and CMS observations. We find that those models allowing early quintessence give the largest variation Δα at the decoupling epoch. Furthermore, the fifth force experiments imply that Δα/α is less than about 0.1%.