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Updated: Jun 18, 2026

Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
A pH activated configurational rotary switch: controlling the E/Z isomerization in hydrazones
Shainaz M Landge1, Ivan Aprahamian
1Dartmouth College, Department of Chemistry, Hanover, New Hampshire 03755, USA.
Abstract:
The replacement of one of the carbonyl groups in a 1,2,3-triketone-2-naphthylhydrazone with a pyridine ring yields an original molecular switch that can be switched fully, effectively, and reversibly between the E and Z configurations. This hydrazone-based, pH-controlled, molecular switch is the first example of a chemically controlled configurational rotary switch. The bistable switch exists primarily (97%) as the E configuration in solution and can be converted quantitatively to the Z-H(+) configuration upon treatment with trifluoroacetic acid. When Z-H(+) is passed over a plug of K(2)CO(3), the "metastable" Z configuration is observed using (1)H NMR spectroscopy, which thermally equilibrates to give back the E configuration. The rate of this process is dependent on the polarity of the solvent, indicating that the E/Z isomerization takes place via a rotation around the hydrazone C=N bond.
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