Kinetic study of azobenzene photoisomerization under ambient lighting

Laboratory illumination is sufficiently intense to produce a photostationary state (PSS) of amphiphilic azobenzene compounds in water. We observed [cis]PSS/[trans]PSS ratios equal to 0.33–1.2 in D2O and 0.37 – 3.8 in dimethyl sulfoxide-d6. ortho-Fluoroazobenzene amphiphiles produced 2–3 times more cis-isomer at equilibrium compared to non-fluorinated compounds which is explained by the isomeric variation in optical absorption profiles. Isomerization kinetics were measured using UV–Vis spectroscopy and the ratio of trans-to-cis over cis-to-trans rates does not quantitatively correlate with the observed PSS. The kinetics define the timescale of ambient photoisomerization where the half-life for PSS formation is 40 min for the fluorinated compounds and 80 min for non-fluorinated compounds.