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Azobenzene derivatives can be used to reversibly photoregulate secondary structure when introduced as intramolecular bridges in peptides and proteins. Here we report the design, synthesis, and characterization of a disubstituted N,N-dialkyl azobenzene derivative that absorbs near 480 nm in aqueous solution and relaxes with a half-life of ∼50 ms at room temperature. The wavelength of maximum absorbance and the rate of thermal relaxation are solvent-dependent. An increase in the percentage of organic solvent leads, in general, to a blue shift in the absorbance maximum and a slowing of the relaxation rate. In accordance with the design, the thermal relaxation of the azobenzene cross-linker from cis to trans causes an increase in the helix content of one peptide where the linker is attached via cysteine residues spaced at i, i + 11 positions and a decrease in helix content of another peptide with cysteine residues spaced at i, i + 7. This cross-linker design thus expands the possibilities for fast photocontrol of peptide and protein structure.