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(September 29, 2015) Molecular
motors are synthetic chemical compounds that can convert externally supplied
energy into mechanical motion. Such molecules, which are specifically designed
to execute directional movements in response to a specific stimulus, are an
essential precondition for the construction of useful nanomachines. Among the
most promising types of molecular ‘engine blocks’ are substances whose
three-dimensional conformation can be altered by exposure to light. “However,
all the light-activated molecular motors described so far utilize UV light as a
power source. But this severely restricts their potential range of application,
as its high-energy photons may have deleterious effects on the nanomachinery as
a whole,” explains Dr. Henry Dube, who is at LMU’s Department of Chemistry.
Dube and his colleagues have now found a way around this obstacle: They have
developed a novel class of molecular rotor that can be driven by visible light
– which is less energetic than UV radiation and therefore less likely to
compromise the operation of more complex systems. The researchers describe the
compound and its properties in a paper published in Nature Communications.
The basis of the newly developed molecular motor is the
molecule hemithioindigo. Hemithioindigo is a photoswitch, which is made of two
organic molecules, which are connected by a carbon double bond. Exposure to
light alters the structure of hemithioindigo, causing it to rotate about the
central double bond. In contrast to the light-activated motors previously
described, rotation of the hemithioindigo-based motor requires the less
energetic visible light – and it rotates extremely fast: The researchers
demonstrated that the molecule rotates – unidirectionally – about 1000 times
per second at room temperature. “We ourselves were surprised that the motor
works so well, for it is known that many molecular motors do not steadily
rotate in one direction, but also revolve in the opposite sense to some
degree,” says Dube. “Given the complexity involved in the design of such motor
molecules, it is really astonishing to that we gained complete control over the
direction of rotation at the first attempt.”