In one aspect, a chemically-modified siRNA for reversible photo-controlled gene silencing is provided. In one embodiment, one or more nucleotides the sense strand of the siRNA are replaced with a spacer comprising an azobenzene or derivative thereof. The azobenzene or derivative thereof undergoes isomerization between the trans-configuration and the cis-configuration in the presence of light from a light source and the siRNA optionally has higher RNA silencing activity when the azobenzene or derivative thereof is in the trans-configuration compared to the cis-configuration. In other aspects, the chemically-modified siRNAs may, for example, be useful as both therapeutics and research tools.
