Described herein are dimethyl acetal-containing UV-absorbing compounds and their uses in preparing UV-absorbing polyvinyl alcohol prepolymers suitable for producing UV-absorbing contact lenses capable of blocking ultra-violet (“UV”) radiation and optionally (but preferably) violet radiation with wavelengths from 380 nm to 440 nm, thereby protecting eyes to some extent from damages caused by UV radiation and potentially from violet radiation. This invention also provides a UV-absorbing polyvinyl alcohol prepolymer.