Molecules move in response to light

Molecules of a substance known as methyl red respond to polarized light by moving in a way as to block the light. Ms. Yu-An Lo, of the Metallurgy and Materials Engineering department, has been researching these molecules for her Ph.D. and has discovered some unique properties. The molecule, Aminoazobenzene derivatized-methyl red, is dissolved into a solvent and then deposited onto a silicon dioxide (glass) substrate. The glass with the methyl red is then heated and allowed to cool, in a process called thermal relaxation. After the thermal relaxation, the glass is then exposed to filtered, polarized light and allowed to rest. In a matter of seconds, the molecules of methyl red will orient themselves to oppose the polarized light, evidenced by the glass plate turning black. The glass is then rotated and the same effect is observed.

This effect of methyl red responding to changes in polarized light is similar to how liquid crystal displays (LCD) in computers work. The liquid crystal molecules are captured between two conducting plates, and a voltage is applied across the plates. The molecules then orient themselves with respect to the light that is passing through them, allowing only the desired wavelengths through. This effect can be tuned using different voltages or different wavelengths of light.

Lo went on the discuss how different wavelengths of light produced an altered response from the methyl red. It seemed that at certain wavelengths the molecule would undergo “isomerization,” a process by which a chemical is altered in its chemical and physical state and exhibits different properties from the parent chemical. After this isomerization, the molecule’s absorption of light increased dramatically, effectively blocking all visible light. One possible reason for this, Lo explained, might be because of the oxygen in the environment under which the experiment was conducted. A member of the audience postulated that if you were to conduct the experiment in a pressurized nitrogen environment, you might experience different absorption from the molecule, to which Lo confirmed that it was possible.

As the experiments were conducted, Lo discovered that the photo-active methyl red gradually stopped responding to the changes in polarized light. It seems that methyl red degrades much the same way that photovoltaic cells in solar panels degrade due to exposure to sunlight. Lo experimented with various environments to determine if the lifespan of the methyl red monolayer could be extended. She found that cooling the glass plate had some affect and that as the methyl red absorbs light, the energy of the molecules increases, thereby heating the monolayer until the molecules begin to degrade and are no longer able to respond to changes in light.

These molecular interactions are not well understood, “And that is why I want to study them,” Lo said. And while Lo did not specify any real-world applications that might be found from this research, it would seem that through extended experimentation and a deeper understanding of what causes these reactions and interactions, applications and uses for this methyl red technology would soon become evident.

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