"When exposed to visible light, the dithienylethene became colorless again and the worms' paralysis ended. Many of the worms lived through the
paralyze-unparalyze cycle. Scientists were not sure how the switch causes paralysis."
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Diarylethene
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In chemistry, diarylethene is the general name of a class of compounds that have aromatic groups bonded to each end of a carbon-carbon double bond.
The simplest example is stilbene, which has two geometric isomers, E and Z.
Under the influence of light, these compounds can generally perform two kinds of reversible isomerizations:[1]
E to Z isomerizations, most common for stilbenes (and azobenzenes). This process goes through an excited state energy minimum where the aromatic rings
lie at 90° to each other. This conformation drops to the ground state and generally relaxes to trans and cis forms in a 1:1 ratio, thus the quantum
yield for E-Z isomerization is very rarely greater than 0.5.
6π electrocyclizations of the Z form, leading to an additional bond between the two aryl functionalities and a disruption of the aromatic character
of these groups.[2] The quantum yield of this reaction is generally less than 0.1, and in most diarylethenes the close-ring form is thermally
unstable, reverting to the cis-form in a matter of seconds or minutes under ambient conditions.
is thermally unstable, reverting to the cis-form in a matter of seconds or minutes under ambient conditions.
Thermal isomerization is also possible. In E-Z isomerization, the thermal equilibrium lies well towards the trans-form because of its lower energy
(~15 kJ mol-1 in stilbene).[3] The activation energy for thermal E-Z isomerization is 150-190 kJ mol-1 for stilbene, meaning that temperatures above
200°C are required to isomerize stilbene at a reasonable rate, but most derivatives have lower energy barriers (e.g. 65 kJ mol-1 for
4-aminostilbene). The activation energy of the electrocyclization is 73 kJ mol-1 for stilbene.
Stilbene isomerizations under the influence of lightBoth processes are often applied in molecular switches and for photochromism.[4][5][6]
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