A Wavelength Effect on Urocanic Acid E/Z Photoisomerization*

E‐Urocanic acid exhibits a single, featureless, long‐wavelength absorption band with λ max ˜258 nm in water. However, the quantum efficiency for E→Z photoisomerization is wavelength dependent in this region, with the maximum value at the low energy edge of the band (e.g. 313 nm) and appreciably lower efficiencies measured at ≦ 300 nm.