 OK, so good afternoon, everybody. My name is Sandro Scandolo. I'm here from the ICTP. And it's really a pleasure for me to welcome today Petra Rudolf. Actually, we know each other since many, many years. We don't really say how many, but it was a long time. So actually, she spent some time here in Trieste doing research at the task, the National Surface Science Lab. So Petra studied in Rome at La Sapienza, where she specialized in solid state physics. She then came to Trieste to work a task, the surface science lab here for about five years. She spent time also at Bell Labs. And then she went to Namur in Belgium, where she got her PhD. And she became postdoc. And then finally, she got a chair in Experimental Solid State Physics at the University of Groningen in the Netherlands. So her main interests are in the field of surface science, condensed matter physics. In particular, she's been working on molecular motors. And the title of the talk today is precisely about molecular motors. She's also worked on organic theme films in organic, organic hybrids. She also got a number of honors and awards. She got the Descartes Prize of the European Commission in 2007 for her work on molecular motors. She was even knighted by the Queen of the Netherlands in 2013. Congratulations. She's a fellow of the American Physical Society of the Institute of Physics. She's a honorary member of the Italian Physical Society. And recently, this year, she was elected as president of the European Physical Society. So today, she's going to talk to us about the molecular motors and switches at surfaces. Petra, please. Welcome. Thank you very much for this kind introduction. And thank you all for coming so numerously to this colloquium. I'm especially grateful to the ICTP, not only for inviting me today, but for the beginning of my career of making their library available. Because we are talking about the times where you couldn't search things by Google, you had to go through the books of abstracts and then find the papers. And the ICTP was a very, very valuable source that helped us to do our research. So one of the research themes that Sandra told you of my group is molecular motors and switches on surfaces. And I would like to start this talk by asking you, do you really know how your muscles work? And in order to show you that, let's see if it works, let me show you what really goes on inside your heart when it's beating. You see this? This is what happens there. We will go in in more detail. And you see here is your little molecular motor that picks up the fibers and moves them along. And this is why your heart beats. And molecular motors are really an essential part in many things that nature does. Here is another example of a motor protein, a very nice movie that the colleagues of Harvard University gave me. And if you look at the screen, you see many, many different things in our bodies and in nature in general that work with molecular motors. And the essential thing is that nature works very differently from how we do. Because when we think, especially as physicists, about the function of something, we think of a material which has specific properties, usually static properties. It conducts heat. It conducts electricity. It is transparent. Nature does a lot of things in a dynamic way. Molecular motors work together to make a change at the macroscopic level come about. So as humankind, we really have a duty to learn from nature also in this. And what I'm going to present to you today is our Neanderthal stage, where we are in learning how to do this with synthetic molecular motors. So here there are examples of synthetic molecular motors. I work in the same university as Nobel Prize winner Ben Feringha, who got the Nobel Prize for Molecular Machines. So I also collaborate with him. And what you see is that this motor is so much more primitive than one of the nature's motors that I'm showing you next to it. It doesn't want to work. Well, it moves. And this is what you see there. We are not very good at directing the movement of molecular machines yet. Not at all as efficient as nature is in doing that. And when you think of biological machines, you have to think that they are very different from the machines that we use on the macroscopic scale. First of all, they are soft and not rigid. They work at completely different temperatures than the motor in your car. They use chemical energy in this. They are similar. Very often they work in solution at surfaces. Crucially, they are made by self-assembly. So it's macromolecular chemistry, which helps us a lot to have the right machines. And as I will show you, the different parts are often connected by non-covalent bonds. They rely on Brownian motion and on the fact that you make an architecture in which you control, you restrict the freedom that are accessible by the Brownian motion. What you need to know is that the components are constantly in motion. They are not blocked as we can do with the macroscopic thing. And they are governed by statistical mechanics, not by Newtonian mechanics. So these are very important differences. And just to make you understand, while you have obviously heard that nano-objects in the future should be used to do useful things, but because of their nature, nano-machines are very difficult to control. The propulsion system with great difficulty causes them to move all the time. And then whenever they see a surface, they stick. Except if they are bacteria and viruses, they have learned very well to get where they want in our bodies without sticking everywhere that they come by. So the molecular machines that I started to work with when I started in this business are these two, the rotexan and the catenan. So as you can see here, let me now figure out which is the, yes. So you see here bifurcated hydrogen bonds. So you have a staff, the yellow thing, and a ring as designed here in a schematic way. And this ring can go on different positions on this staff. And then you have stoppers so that the ring does not fall off. So these are the stoppers. The ring is held in position by these bifurcated hydrogen bonds. And when you tickle them in a certain way, the ring can move from one station to the other. In the case of the catenan, the ring moves on another ring like the Olympic rings. They are threaded one into the other. So these particular molecules were actually discovered serendipitously because David Lee wanted to make a macro cycle that could catch CO2. So he thought of this reaction combining these two parts to make a ring like this in which the CO2 could be trapped. But when they analyzed the molecule afterwards, they found that what they had made was this. One ring threaded into the other. And then, of course, there is no room for any CO2 because the electrons already occupy all the space. And at this point, he had learned how to thread one part into the other. And then you can make rotexans. And when you have a rotexan, you have much more interesting things that you can do because you can have a functional group on the ring, which when it is close to another functional group on the stopper does something. And when it is far away, it does not. Or you can change the movement. You can make them change even the shape. That will change when the ring is somewhere and somewhere not. So there are lots of possibilities. How do we know that the ring moves at all? Well, the most simple way is to have a fluorescent group here and then to put it in two different solvents. So when it is in this solvent, the ring is close to the fluorescent group. And so no light is emitted. Instead, when you put it in this solvent, the ring likes much more to interact with the solvent than to interact with this group. So it's far away, and you get the fluorescence. But if you want to do anything with these machines to change the solvent, it's not a particularly convenient fashion. So changing it with light is much better. And this is what I'm showing you here. So essentially what happens there, these are experiments of my colleague, Sandoval Tusson, in Amsterdam. And the reason I'm showing it to you is that you have to think differently about molecules than you think about macroscopic things. So what is happening here? We go with a photon on this part of the molecule. And by that, we do a photoisomerization here. And then the ring does not want to sit here anymore, but it wants to sit close to this part. And now what Walter did is to follow this transition of the ring with time-resolved infrared spectroscopy. Because these vibrational modes here will be different when the ring is around or when they are free. So here it is free, and here there is the ring around. On the other side, this one will vibrate differently when it is free and when it is involved in this double hydrogen bond. So by taking spectra and looking how these vibrations change, you know something where the ring is at the time. And this is what you're seeing there. So these are time-resolved infrared spectra. And you see how the molecule arrives. And you see how the molecule leaves. And then you can, as a function of time, how many molecules are in one state or in the other. And then you can analyze the spectra and learn something how quickly the ring moves. And he did that. And what he did was to make the staff longer and longer. And then to look how much time it takes. So here you have it just for one length. You see that slowly, slowly the molecule arrives in the final condition. And in the other case, you see that it leaves the starting station. And so from this, you can compute the transit time. And you see that the transit time is very short. Now you make this molecule, the staff longer and longer. And essentially, I thought that you make it longer and longer. It takes longer time to get to the final state. But so what? Well, not so what. Because if you look at the data and you analyze them just with the length of the staff, you should have the points that are on this curve. Instead, what you see is that the points are on a completely different curve. So when the ring goes from one station to the other, it does a random walk. As we expect, it goes back and forth before it lands in the new potential well. But there is a bias for going back, not for going to the place where you want to go. So these are surprises that you get when you work with molecular motors. Your intuition, like so often when we go to things that are governed by quantum mechanics, your intuition does not necessarily help you. So what I do with these things has to do with the fact that a single layer of molecules can change a lot. I don't know if you know the story of ice. Ice is slippery only down to a certain temperature. Because down to a certain temperature, the first layer of ice is still liquid. And that makes ice slippery. If you go further down in temperature, also the last layer freezes. And then ice, walking on ice is like walking on sand. And this is what happened to poor Scott when he went to discover the South Pole. Because he made many mistakes. But the main mistake he made was leaving too late. And the temperature was too low for his slays to be of any use. And that's one of the reasons why he died of exhaustion with his whole group. So what we want to do is not to leave it to nature what the molecules on the surface do, but to decide what we want them to do. And the idea was the following. We had this idea when we were still working with catenants. Later on, we realized it with rotexans. But the idea is the following. You prepare a surface with these molecules that can change. Where first, well, you have one part of the molecule which is hydrophilic. It likes water. And one part of the molecule which makes the surface hydrophobic so it can't be wetted. So if you start out with a surface that cannot be wetted. And then you come with the light where you want the droplet to move. And you change the molecules here. Then the droplet will go there, wet the surface. And then after some time, this is an excited state. You have excited it with light. So it will decay. And you go back to the situation where you were before. But the droplet has moved because by changing the molecules from here to there, you have induced here a different surface energy than here. So you have made a gradient and the droplet can move. And we tried that. And the first thing that we did, surface scientists, what do they do? They put their molecules on the surface right away. That doesn't work in this case. Because we have the ring and we have the stuff. And when we put this molecule on the surface, both of them will be bound to the surface. And nothing moves anymore. So we have to be more clever. And we have to just fix one of them. And we decided to fix the ring. And we do that by first putting a self-assembled monolayer. That's these molecules there. And that will self-assemble on the surface. And they have a functional group here. In our case, an acid group that will react with a functional group of the ring. And then they make a bond. And only the ring is bound. And the stuff which can be in there is not bound to the surface. The way to do that is very simple. You first build up your self-assembled monolayer. Then you put it in the solution with the rotexanes. And after a few days, you have your surface covered with rotexanes. Well, actually, I did not tell you yet what kind of rotexane and why we are using a rotexane. Well, in our collaboration with the chemists, they were not able to make a catenone that would satisfy our requests. So we changed. And the inspiration came from Teflon pans. Why can't you put water on a Teflon pan and make the Teflon pan wet? Because there is fluorine. And the fluorine makes the Teflon pan what it is. So our clever chemists thought, if we put some fluorine atoms on the stuff so that they are exposed when we start, and then later on we move the ring over there, we should have the function that we want. And the way this works is the following. We could prove that it works in solution. So you have this molecule with the fluorine here. You shine light on it in solution. And what happens? Let's see if it does what it does. Yes, it changes. And because we have fixed the ring, it's the stuff that moves and not the ring, but the result is the same. Let me just go back to show you what happens, why does it move? Well, I told you you have these bifurcated hydrogen bonds. Now, when you do a photoisomerization on this group, this group looks like this. And then you cannot make these bifurcated hydrogen bonds anymore, so the ring cannot bind here anymore. And then it goes over the bulky fluorines where it really doesn't want to go, but it has no other choice. This is what I meant with designing the architecture of our system so that it does what we want it to do. Okay, so then you have it on the surface like that. You have bound it there. The ring is bound. It is in this situation. The fluorine is exposed. You come with the light. You do the photoisomerization that's indicated by the color change and the stuff will move. And now the fluorines are covered and this should work. How do we know that it works? Well, we look at it with photoelectron spectroscopy. There are a few people here in the audience who know how that works. Essentially, you find the signal of the self-assembled monolay and of the rotexan in the spectrum of the surface, especially you find the fluorine and the nitrogen which were not there before. So you know that you have the combined system and you can trace all the elements and learn that they are there. You can also look at it with atomic force microscopy. This is the gold before we emerge it in first in the solution of the molecules that we use for anchoring. And later on, after we have put the rotexans, we see these white spots, not too many of them. Actually only two to three percent of the anchoring molecules actually anchor something. Now you say, well, there's a lot of space here. Yes, and there has to be because we have a system which moves and which can turn the molecules fixed only in one point. So you will never get a very dense assembly. You get only a situation which looks like this. Well, does it work? Well, I can show you that it works because if you put a droplet on the surface as we prepared it, it does not really wet the surface well. Then I illuminate the surface and I put the droplet again and look, now it wets it. So it works. Then we can say, okay, but can you also do what you want it to do? Namely, to move the drop. Light on, here it goes. We can do it also with a bigger drop. It moves a bit more slowly, but it still moves. And then of course, we are physicists. So we want to show that we can do work, right? And how can you show that by making it moving uphill? And you can do that as well. And then you can calculate the work against gravity. That's not all the work you are doing because actually the work against the viscous forces is about the same, only that it's much more difficult to calculate it and to determine it precisely. So you just calculate what is your work against gravity. Then you know what is the density of your molecular shuttles. So you have about one molecular shuttle, one rotexon every three square nanometers. You know how many molecules are under your elongated drop. And then you have to make an assumption how many molecules actually change their configuration. And what we did is to assume that on the surface, it's the same amount as in solution. That is 40% that isomerized and you get a number for the potential energy change and 50% of the total free energy made available by the nanometer movement goes into gravitational work. That tells us something else because a special thing about molecular machines in nature is that they don't waste energy. Our microscopic machines produce a lot of heat that is just wasted. Biological machines don't do that. And from these numbers, you can conclude that also our synthetic molecular motors when they do microscopic work, they don't waste energy. So apart from getting us a nice prize and showing that this is actually possible, there might also be practical applications for this kind of thing. You could, for example, think to make biochips where you now don't need microfluidics to move your droplet, you move it with light. And to do things with light, we know perfectly well, we have our CD players, we have everything, how we miniaturize lasers. So all I've shown you is done with a normal lamp, but of course you can also do it with a laser with the right wavelengths. So you could use it to do a biochip in which you put your droplet of blood or you put your droplet of urine and you bring the drop to different places where it is analyzed. Then you plug it in your phone and the data go to your doctor. So in order to show that you can actually move droplets one towards the other, we did this little proof of principle. So now you catch me because I never told you what the liquid was. Actually, we never managed to do it with water because water is far too polar. So we did it with diodomethane and we proved that the diodomethane has no part in this game. It's really only the molecular motors. But here in this experiment, what we did was to put a little droplet of NaOH in water here on top of one of the droplets and then a suspension of bromothymal blue in the other droplet. Now for those of you who don't know what bromothymal blue is, that's what one does pH tests with. So if it is blue or if it is red that tells you what the pH is and here we are doing the same thing. So we are now moving the droplets towards each other and when they meet, they react and you get the blue droplet there. So in principle, it works. You could also think of using this technology not with these red accents because they are far too expensive but with the cheaper molecule, I'll show you some other molecules later on to make offset printing. Offset printing is a much more ecologically friendly way of printing that was used when I was in primary school and you used water soluble inks and you printed with those. Now, right now we use all the black stuff which is not easily recyclable, et cetera because we have no way of writing and erasing but with such a system, you can make a surface which can be written with light and which can be erased with light. So that might be a way to go and there are some companies who are working on that. So what I've shown you now was the work of Sandra Mendoza who is now back in Argentina and Monica Lobomska who is at the ASML and what I'm going to show you now is, sorry, the work of Monica with Tatiana who is also now at ASML and it is on Benfergas motors which are like this. So essentially you have four states. Again, there is an architecture because with the light you bring it in an excited state which is not stable which then thermally relaxes to a stable state and then with light you can again move into an unstable state which relaxes to your starting state. So you have this thing which goes like this and then like this and goes around. In fact, you can fix it on the surface in different ways. You can either fix it on the surface with links put here and then you will have a nano merry-go-round which will turn like that or you can make a nano mill. If you put the legs on this part, it will turn like this. Okay, how do you put the legs? Well, that depends on which surface you want to functionalize. So we have developed a whole series of functions on the legs that will bind to the surface we want to use and this is how we put them on the surface. How do you see whether they still turn on the surface? Well, the point is that these are chiral molecules. So if you look at their chiral spectrum, here you see it in solution, you see that when they are in one state, the stable hum and the photo excited, they have a different signature in the dichroic spectrum. Then in the other one. And now if you look carefully, you see that you have the same one. Unfortunately, my color scheme is not well made because the red one has now become black. You see that you get the same on the surface and also the other one, the blue one, you can find it back here, red on the surface. So from this, we know that they turn on the surface. You can also ask yourselves, how do you put them on the surface and we're using different kinds of chemistries. It's not so important, but the chemists are fantastic in finding new ways of how we can fix them on the surface and it works very well. And then you can ask yourself, actually, are these methods good? Because if I have my motor fixed with two legs, then what I see is actually the motor which chirts. But if my motor is only fixed with one leg, what I could be seeing is this, right? Because only one leg is fixed and this is not what we want to do here. So we prove that actually by spectroscopies that both legs are fixed to the surface and that these methods function, we don't get any signature anymore here in the infrared of this free group here. So we can do it, we know how to do it. I'm telling you this because referees have bugged us a lot on that. So then also these motors, they turn on the surface and what is fantastic about all these machines is how robust they are. The Rotex samples that I showed you before, you can keep them in your drawer for months as long as they don't see light. You take them out again and they work like they worked on day one. And the same is true for Ben's motors. So it's really very nice systems and so we tried with them the same games of making droplets move and so on. They did not move with water, so that was lost time. These motors are very expensive to make, many various steps and so on. And so we also work with switches which are easier to synthesize, easier to functionalize and they are also addressable by light and by charge. And I will show you a very short example from the work of Alexei Ivashenko now in Oslo. So the molecule that we are looking at is a very simple molecule like this and you can imagine it like a baby with arms and legs and then you get different ways in which the legs and the arms are positioned when you make this go into different states. One of them is a bit like the exorcist but we don't want to push this comparison too far. So when you put these on the surface you get the same things as you get in solution. You have barriers in which you can go from one to the other and you can stimulate the molecule to transit by light and by charge. And this is by charge. So here you have the molecule on the surface. You give it charge and you see that the contact angle changes which means that it goes into this new state and you reduce it and it goes nearly back where it was and you can follow these changes with different spectroscopies and see what your molecule does. So if we follow the contact angle we see that we can go back and forth many, many times by light and by charge and it behaves quite well. I want to show you our latest baby just to show you what exciting things you can do. So this is a long thread and it has here a switch by which it does from straight to like this, okay? This is the work of Sumit Kumar who just defended his PhD last month and the molecules were synthesized. In Ben's group, Wojtek did the synthesis. He also defended last month. So if you now take this thread and you put a ring around it, in solution they saw that actually when you switch this part of the molecule goes out of the ring and it not only goes out, you can also switch back and it will hide in the ring again. And so we said we have to try out whether this works on a surface because this might give us quite a dramatic change in contact angle and maybe it works for water. So this is how you can demonstrate that it works in water in the liquid and there it works and it works very nicely. You can see that you can switch it back and forth. You can follow it with the UV-Vis absorption and you know where you are and that's what it does in solution. And you can do it many, many, many times. It doesn't get tired of going in and out. It just continues. So we put it on the surface and now you have the following. You have this part which is hydrophilic and this part which is hydrophobic which means that when it's outside it's like our fluorine before. Our surface is hydrophobic and when it hides our surface is not hydrophobic. So we did that and actually it works in the sense that you get a very dramatic change in contact angle, about 20 degrees. That's very nice but the water droplet still is stuck. So we cannot transport water with this. Of course we did not spend 10 years just trying to transport water. We also did a lot of things. Well this is the explanation why it goes in and so on. I don't want to spend any time on that. I just want to tell you something else which did not work because we tried. Apart from transporting water we also said well it would be nice if you could change the roughness. The roughness of a surface. So have some bulky group which you can bring out and then hide again and bring out and hide again. So we worked together with Klaus Mullen in Mainz and again we had this same switch that I just showed you for the thread that goes in and out of the ring that we have here and so the idea is that when it is in one state the bulky part lies down and then when it is in the other it stands up. So we tried to do this and actually you can put these things on the surface. It works nicely to put them on the surface but when you try to switch them it does not work. To switch them it does not work and what we think is that of course the van de Waal's attraction between these bulky parts is far too big and once they have found each other they don't want to separate anymore. They bend a little bit when you switch it but that's it. So not everything works. Then we went in another direction and we asked ourselves well actually how does the conduction through a switch change when you change the switch? And there we collaborated with Ryan Kierke who is specialized in that kind of measurements. Again it was Sumit's work and again Wojtek made the molecules and this time the molecules are these so the switch is here. This is the situation in which it's disclosed. It's called a spiral pyrin when it's closed and then with light you can open it and it's called signing when it's open. And you can ask yourself how can you measure the conductivity through the molecule? Well actually it's not so difficult. What you do you have the molecules on the surface so they form a continuous layer. You have to learn how you make these layers but that's just like cooking. You learn how to do it and then it works. And then you come with a liquid contact on top and in this way you do not destroy your single layer of molecules because they are quite fragile. But with a liquid droplet you can do that and you can take the droplet off and put it back on and so get some statistics in your measurement, measure different points on your surface. And the liquid that you use is this. It's a gallium Indian alloy and it is a liquid metal on top which spontaneously forms a little oxide layer but you just tunnel through that and the oxide layer is always the same and you can do really big statistics with that. So many samples, many points to get significant answers. So what you see just if you put these alcantiles, you make a longer, longer chain. What do you expect in tunneling? Well you expect that your tunneling current goes in a certain way depending on the length and if you look at the prediction and the experiment you see that it works perfectly. And these are our data. So we have a certain, we collect the current at different potentials, we sweep the potential and we do that with very, very good statistics to get these curves from which you can then get the conductivity as a function of length for example. Now when you switch a molecule, the length can change. Another thing which can change is the dipole and actually you can see that by looking here, nothing switches, it's just two different molecules and the only thing which is different between them is the position of the nitrogen on this carbon ball and by that in one case you have a dipole which is directed like this and in one case you have a dipole which is directed like that and that changes the tunneling current. So that's a second thing that could happen when we have a switch, not only the distance but also the dipole could change. So what you also can have is a distribution in the conjugation pattern of the molecule and that can also influence your tunneling current. So here we have the two states and here we have the measurements that we did. So in the beginning what we did is we just put the molecules. We saw a significant difference but it was not particularly strong. Then we said, well maybe they are not switching very efficiently because there could be hindrance between the switches. So let's space them a little bit and we made a mixed monolayer in which, well this was the fatigue, we don't care. We made a mixed monolayer in which we absorbed spaces between them, exon-file molecules between them so that the switches, there are lots of switches on the surface but they don't touch each other anymore. And now you get a much bigger difference in conductivity which can be very nicely explained by the change in distribution of electrons. This is what the charge looks like when the switch is closed and this is what the distribution looks like when the switch is open. So the electrons which tunnel through here, they see a completely different situation here than here and that's the explanation why the tunneling current is different. I'm nearly done, I just want to show you that you can use these mixed monolayers to encode information on the surface. So you write with the light as I showed you and then, so this is the writing or the erasing and then you use an acid or a base to lock the molecule in that state and then you can read it out and you can erase it as you wish. Again the same people involved in the study and here you see exactly what we are doing here. So the red is the, it's all the, we have it in this state. We lock it with the acid, then we shine the light on it but nothing moves, it stays here. Then we unlock it and it switches and we can read it out again and we can lock it also in the other state if we want. So essentially you can read and write with these two states that we have. And so we made a little chip of that because now we have to go with the liquid so you have to have a place where you put your acid or your base to lock the molecule and we wrote on it so we made such a soft punch card and it works very, very nicely. You have only three erroneous bits when you read which is completely normal for chips where you read. We could erase 100% successfully when we rewrite and read again, we have one erroneous bit. So this is actually a workable chip. You might have your doubts about using acids and bases to lock it but in principle, this can work. So that was what I wanted to show you today. I hope you enjoyed my molecular modus and switches and I thank you very much for your attention. Thank you very much, Petra. Questions or comments? Well, let me start with the first one then. I mean for macroscopic motors, I mean the number of cycles is the typical, I mean parameter that you look at to determine the quality. The nanoscale, you've shown some examples where you actually have problems reading, writing, but also, and there are also probably different mechanisms while mechanical degradation is the principle of mechanism. The nanoscale, there's term of fluctuations. I mean, can you give us some hints about this? Yes, so we have just published another paper where we look at fatigue actually. I don't know if it's out yet. It was accepted a couple of days ago. So anyway, what we could show is that these organic molecular switches are extremely, and when I say extremely, I mean extremely sensitive to water vapor. So we tested the same switch in just a normal flow box, which is normally considered good enough when we measure the transport properties and then we put it in a special glove box with especially low oxygen and especially low water. And we checked our switches for fatigue for the mission spectroscopy where you see if any changes have happened. And what we see is that the switches many, many times in the water-free, oxygen-free environment, nothing happens to them. You can run them for hundreds of times and there is no fatigue whatsoever. Really small amounts of water and oxygen, as you have them in a flow box where you work with the nitrogen flow, are enough to destroy your switch in the long term. And you see it also if they have considerable fatigue, you can prove it spectroscopically. For questions, yes. You started your talk talking about the heart muscles. And bio-tissues are made mainly by biopolymers like protein which are amino acids. So how you carry over these results which I suppose are for small molecules to biopolymers like protein or I don't think DNA, which is mainly in the cell, but let's say about proteins. It's a whole chain of amino acids, how they work. So what's your question? My question is, your results which you showed, I suppose they are for small molecules, right? Your talk you started about the heart muscles. Now muscles, they are bio-tissues which are mainly proteins. Now proteins has long chains. No, no, no, but the molecular motor is just the two hands, huh? It's a tiny little thing that that's the molecular motor in this business. The long chain has no active function there. It's just that the tiny motor attaches to the protein and of course there are interactions in special places otherwise it wouldn't attach and then it's the motor which moves. Okay, it's a different kind of function than you see it. No, it's just a different movement for a different purpose. But the size of the motor is approximately the same as the ones that I use. Okay, thanks. Wait, wait, wait for the microphone. What are the dimensions of your soft chip that you showed at the end? This, they're big, yeah. But it's a proof of principle that you can do it. I mean, it's a... So the molecules actually absorb only one photon. Is it a single photon reaction? And if so, what is the actual power of the laser or the light that you need to activate such a reaction? Not much. You can do it with a normal xenon lamp. So you don't need a laser for this. And whether it's a one photon or a multiple photon that depends on the molecule. So we have molecules that we can activate with infrared light because they have a multiple photon absorption. And we don't need a laser for that. We just do it with a normal lamp, black body radiation. So these molecules are really, they just take it when they can get it. So that's how it works. So in theory, you could just do it with a single photon one by one? I don't know if anybody has ever tried that. I know that people have done measured single, single molecule conduction measurements where they shine light on a single molecule and then they look at how the conductivity changes when they switch it. But if it is just one photon that they absorb or not, I cannot tell you how they do it. So this could be a topic for future study. Of course. Yes. Thank you for, you also answered my second question, which was can you, can you use two photon or multiple photon? Yeah, yeah, yeah. We have certain switches where we were getting crazy because we were doing Raman with infrared light. It's intensity and so on and this is how we learned about this. Thank you. Okay, if there are no more questions, before we thank the speaker, let me remind you the rules of the game now. So our colloquium speaker will stay with the students, with the diploma students for a private session with lots of questions. Everybody else is invited for, there are some refreshments outside and we'll make sure there are some refreshments left for you and for the students at the end. Thank you very much. Thank you.