The Molecular Machines Which Dance in the Sunlight

The sun has a strange effect on photochromic molecules.

Dancing in the moonlight is pretty specific to humans. 

It’s definitely true that new things are discovered every day. For example, last week I found out that Rick & Morty is my new favourite TV show. It’s hard to admit, but living such an adventurous, fast paced lifestyle can sometimes be difficult.

When it comes to science though – or at least chemistry – things tend to go a little bit slower. A scientist will typically spend years focusing on just one molecule. For example, in the development of a new drug. However when the drug is made, it is finished; no further developments are necessary. There’s nothing left to discover, and that’s how Dr. David Bléger sees it.

David is the head of his own group at the Humboldt-Universität zu Berlin and as a scientist he has decided to specialise in photochromic switches in order to, well, switch things up. Photochromic switches are considered molecular machines in that they are dynamic and able to move under certain conditions. This offers plenty of exciting opportunities for exploration by scientists, as well as utilisation in the future by society.

Photochromic compounds react to light

Photochromic compounds are essentially compounds which change their orientation in space when exposed to light. This then alters their physical properties (i.e stiffness, melting point, colour). One way of picturing it is like when your parents used to open the curtains to get you out of bed for school. Your reaction to turn the other way is similar to the molecule reacting to light and changing to a different form; though as it lacks a nervous system, the molecule isn’t making a conscious effort to be lazy. Once the light is gone – or the curtains are closed in our analogy – the molecule can return to its usual position.

However, not all compounds behave in this way and they are specifically designed for purpose. Despite telling me that the existence of these compounds had been discovered over 80 years ago, David informed me that there is currently only one commercial use: photochromic lenses. These darken when exposed to sunlight in order to offer more protection against UV light, reduce glare, make you look more attractive etc.

Photochromic lenses which darken when exposed to sunlight. Source: Wiki Commons.

Photochromism can be used to develop future technologies

There are two main fields in which David believes this kind of technology will be utilised: life sciences (i.e medicine) and material sciences. For the former he proposed light activated medicines. These medicines could be used to activate a drug before or after it is inside the body. In turn this could help combat antibiotic resistance by controlling the amount of time the drug is active.

As for his own career, he focuses more on the material side of things and it’s his dream in the field to produce a smart material which could actually do something and provide a function for society. An interesting example he gave me was that of a molecule which could be introduced as a self cleaning layer. He proposed that they could be directly utilised in society. A self cleaning window was the example he gave me; that’s right window cleaners, automation is coming for you too.

However, he explained that they could also be used to indirectly benefit society by increasing the efficiency of solar cells. They would work by harnessing a fraction of the sunlight shining on the cell/window/surface, causing a vibrating movement and thereby removing particulates. One of the big negatives associated with solar energy is that the cells must be cleaned regularly. Even a small amount of dirt affects their efficiency. This is especially true in places where they are most effective i.e deserts. My personal dream would be self cleaning dishes and rooms.  On the other hand, I imagine some people – from teenagers to fully grown men – think this technology already exists.

A dream for the future 

The bad news, unfortunately, is that these technologies will not be ready for quite some time. In 20 years he expects that there could be some functional use, but not a widespread application in society. As a field, it is relatively new in the sense that these types of compounds haven’t been highly studied, despite having been around for longer than my grandparents.

As an exchange student at the Humboldt-Universität, I was lucky enough to work in David’s group for a few months, therefore I could also see for myself how these technologies are in the early stages. By the time I’m the same age as my grandparents, hopefully the technology will be perfected and significantly cheaper; it’s every pensioners dream to have clean windows after all. Maybe even one day I’ll get to sit in my nursing home, rambling on about how I contributed to such a technology through my work in David’s group, while being patronised and shunned by those around me.

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Jack McGovan is a recent graduate in chemistry with a specialisation in ‘Energy and Sustainable Chemistry’ from the University of Groningen, the Netherlands. Following a job as a student journalist covering the energy transition, he has moved to Berlin where he is following his passion for working towards creating a fairer and more sustainable world. Seeing a gap in the way in which the world of science was communicated, he founded Delta-S. By writing source based content, he hopes to communicate his findings to a wider audience.