The thermally stable trans isomers of donor-acceptor substituted azobenzene dyes can be easily transformed into unstable cis-form by light. Students in the physical chemistry lab investigated the kinetics of the thermal cis-trans isomerization of 4-anilino-4'-nitroazobenzene (4A4NAB, also known as Disperse Orange 1) in six solvents of different polarities by means of flash photolysis using a simple camera flash and a regular UV-vis spectrometer. Students were able to follow how the rates of isomerization and the activation energies are influenced by solvent polarity. Using the transition state theory, thermodynamic parameters such as Δ‡H0, Δ‡S0, Δ‡G0, and K‡ of the isomerization reaction were determined, and the results discussed in terms of a plausible mechanism that involves a charged transition state complex and solvent–solute interactions. The experimental design, students’ involvement and learning assessment will also be discussed in this talk.

The kinetics of the cis-to-trans thermal isomerization of disperse orange: A simple undergraduate experiment for the physical chemistry lab

256th National Meeting (2018)

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