 You have the same thing, 20 minutes, I'll give you a warning at 15. Okay, thank you. And thanks to the organizer for giving this opportunity to present our recent work. So, I'm a PhD student in University of Parma, and this is the work on understanding last I had a relaxation for them, I think it's a very big joint experimental and computational study of family activity, the late person study. And this work is also done in a very close collaboration with Professor Eric Eastman Coleman from University of St. Andrews, UK. So, the family activity data sources is mostly used in organic light emitting diet, which is in short called OLED, and they are basically used on mobile screen PV. So if we look at our screen. We have three basic color, red, green and blue. And under each pixel, we have small device and in the device we have ETL, H2L that is electron and whole transmitting layer and in between we have EML where the main photo physics happens. And in that EML, we have our host and emitter. Emitter is the molecule that emits light, which cause that different color. And our main focus for today's talk will be emitter and host is basically helps to change the environment for our molecule. So let us see how it happens. So when we inject electron and whole, they pay ourselves. So they usually have half spin, and now depending on the combination we can have singlet or triplet. And from the spin statistics, we know that we have 27, 25% possibility of singlet and 75% population triplet. And depending on the method from the singlet or triplet, how the light emits, we have three different generations of OLED. The first one comes from the singlet. So initial days the OLED was basically on fluorescence-based molecule where we have the triplet, but triplet was a dark state because it has a different spin. But in this situation, we can see is that as we have 25% population in singlet, we can have maximum efficiency of 25%. Now if there is another way that we can get light out of triplet, we can go to 75%. And that is the second generation of OLED, which is based on phosphorescence. But if we put some heavy metal in our molecule that increase the intersystem crossing between the singlet and triplet, then theoretically it is possible that we get 100% efficiency for our OLED. But here the point is that we have to use a heavy metal. And it's also a spin forbidden process. So though experimentally it is not possible to get 100% and there is not much color purity. And it's also not eco-friendly. And then we have the last method so far, which is called thermally activated light fluorescence. What happens here is that from our singlet, we are getting from fluorescence. That's happening in nanoscale region. But if there is some way that I can convert the population of the triplet from there to the singlet. And I can get light out of there. And that is called delayed fluorescence. It is delayed because we have to make this reverse intersystem crossing between the triplet and singlet. Which is a spin forbidden process and also we are going to hire energy from a lower energy state. So it takes, so it comes around microseconds scale, time scale, but it's happening from the same excited state as from fluorescence but it's just delayed. And delayed fluorescence is a very old term. It is came out in 50 or 60 years before but it was only 2012 when Chihya Adachi from Japan made device out of this phenomena. And it was completely using organic molecule and after that it got huge attention. And it is called thermally activated because we usually prefer the singlet and triplet energy gap to be within room temperature and energy. And recently this process is also used for bioimaging because there is fluorescence imaging and that is a very short time scale. For delayed fluorescence we are again getting the emission from the same state but we can collect our data for a longer time and that's how it's getting attention. So we'll focus on TADF today. So let us see what are the key properties to get a good TADF emitter. I talked about singlet-triplet energy gap and as I'm talking about reverse net decision processing rate, we understand that we will prefer the singlet-triplet energy gap to be small. We prefer it's zero cap. And to do it and to get it from an organic molecule we usually prefer our donor accept a just transfer donor acceptor system. We also prefer that our donor acceptor will stay in such a way that they won't talk to each other. So we prefer an orthogonal donor acceptor system. So in this way, our S1 and T1 should be pure just transfer singlet and pure just transfer triplet. So S1 and T1 will be almost regenerate and will keep us zero energy gap. But here we got a problem. The problem is the spin orbit coupling, which is responsible for the reverse intersystem crossing rate. If they are pure just transfer singlet and triplet, they will keep us zero spin orbit coupling, which is not good. So we want to be completely degenerate state to get it zero energy gap, but we also don't want it to be pure just transfer state because we want the spin orbit coupling. So this entire molecule will be inside the host, so it is also important that we consider how the environment will affect. And this molecule as we prefer that our donor acceptor will be orthogonal, but still that dihedral angle between then donor and acceptor is almost free rotation it will rotate. And that's why it's very important to check the conformational distortion because when the molecule distort the energy gas spin orbit coupling everything changes. Today that is the focus of my talk. And for that I will present to molecule the first one is the matter is the second one is the math by day. They are almost same but here I have one extra nitrogen and because of this extra nitrogen the crystal structure is completely different. So here we can see that this is the DMACC and DRC from the crystal structure they are almost orthogonal, which was something we liked. And he this molecule has a kind of different painting structure. And the optimal image blue light. So my main focus will be DMACC by DRC but sometime I will talk about DMACC DRC the first molecule whenever it is necessary all the computational studies are done in Gaussian system software and just 6 to x functional 631 gd basis and that's just calculation. So first we will look at them at DRC. So when you optimize them at DRC the in the ground state the DMACC and DRC the donor acceptor was completely orthogonal. And we got completely degenerate S1 T1. Here we can see that it's a jazz transfer where the jazz transfer is happening from the donor to acceptor. And in this situation, we got zero spin orbit coupling that says that we have no risk. But we know that my case is a blue day. So the structure in the ground state is not the same structure in the excited state. So we try to optimize my excited state and when you optimize. We saw that the S1 stays at orthogonal, but for the template, the structure relaxes and it relaxes around 60 degree. So we wanted to do it a more systematic way and we did it rigid. In the rigid schedule scan, we don't allow the molecule to relax. We just take, we just rotate the DMACC, the donor and acceptor. And we plot our energy. So here we can see is that the ground state that is S0 has a minimum around 90. That is something we got from the optimization material, but when we rotate we move from the angle the energy increases for the S1, which is the singlet first singlets jazz transfer singlet. It also has minimum at 90. But if we look at triplet, we see is that triplet comes down, it keeps a double minimum around plus minus 30 from 90. But when this happens, there are two things. The first thing is that the spin or the energy between the singlet and triplet increases, which is the black line here. And we know that it is not good for a TADF because we want zero energy. But at the same time, the spin orbit coupling increases, and that is good for a TADF system. So, from this point, we immediately understand is that the first thing I told that it's, we want just transfer but we also don't want so just transfer. And it's important that we look at both the parameters. So, what we understand from here is that in the grounds that we have our tonal geometry in the excited state molecule relaxes. And because of the relaxation we gain some spin orbit coupling. And from that spin orbit coupling. There is a reverse intersystem crossing between some middle and triplet, and that's how it becomes a TADF emitter. So, we wanted to do a same approach for our next molecule, which is to map ideas. We went for a tonal geometry, we did the scan. Here I'm showing some more higher excited state which was triplet localized on acceptable donor but you can see that they don't interfere much in the process. So, what we can see is that when we go with the optimal geometry of the MAC by THC and we rotate the single triplet comes down because of this nitrogen, the homo-lumo gap decreases and the single triplet comes down. But still this scan does not give us the idea of having a bench geometry in the crystal structure. So, we don't get what we wanted to get. We get a relaxed geometry scan. What we do in the relaxed geometry scan is that we rotate our donor acceptor and then we allow our molecule to relax but we don't allow the trihedral angle between the donor and acceptor to relax. And in this way, we can get the orthogonal geometry. So, first this dotted line was related to the orthogonal geometry which did and then when we did the relaxed scan. We can see is that we can get the bench geometry out of our scan for both the structure for the MAC by THC as well as the MAC by THC. But what is interesting here is that if we look here that solid lines gives that the orthogonal geometry to be the lowest energy geometry for the MAC by THC which is correct that's the crystal structure. And for the MAC by THC we see that the bench geometry is the lowest energy geometry from this scan and that is also correct because that's the crystal structure. And for the MAC by THC we get a transition stream but we are not interested for that. So, what we understand is that for the MAC by THC it was enough to go for a rigid dihedral scan and we understood things. But for the MAC by THC to understand it, we had to go for a relaxed geometry scan and it's kind of give us the idea of plastic geometry. So now on these solid lines which is relaxed geometry we did, we ran our DDTFT. So here we will try to just look at the red line and black blue lines which are simply all just transferred on triplet green lines are localized state and we are not currently interested for those. So if we look at the second structure here. That's the first thing that comes here is that the blue line that is simply it has a minimum around 90. So the idea from here is that we start from a bench geometry, the molecule is excited, but if we allow the molecule to relax, the single will come to 90. But in case of triplet it is not very clear from this geometry, and we can run full geometry optimization and we'll see that later. This is what we get from this scan here but in case of demarcation, the S1 optimized geometry stays at 90. That was also something we saw before for triplet. Here we can see that the minimum comes around 60 that was also something we saw before this one is here we have another minimum but we have checked a lot of times. There is not much population, I mean we never found any population here. So we ran the full optimization of single for TMAQ by THC and when we optimize it, we always got orthogonal geometry. So we just kind of similar to demarcation. Let us look at the spectra now to understand it. So if we look at the spectra, the first thing which is clear the solid line is absorption and the dotted line is emission and in this direction the polarity is increasing. So the first thing is that the absorption spectra of demarcation by THC is blue shifted that says is that the energy gap between the ground state and the excited state for the demarcation by THC is higher than the demarcation. And that's possible if we consider the main geometry without monogymetry. But the next thing which is much more clear is the stroke shift. For demarcation the stroke shift is very small, but for demarcation by THC that stroke shift is very high. And this large stroke shift can be explained if we consider the large relaxation of the second molecule. So now if we look at our oscillator strength for the orthogonal and the main geometry, there is that experimental data that says that the oscillator strength of the second molecule is 20 times higher than the first molecule. So the first molecule when we stay at 90 degree, it's a pure just transfer excited state. So the oscillator strength is calculated oscillator strength state zero. But if it's a main geometry for the next one, the oscillator strength is much more higher that comes around 1.2. And that is exactly something we get from our experimental data. So you have five minutes, it's 15 minutes. So the idea of the main geometry in the ground state and orthogonal geometry in the excited state for the second molecule is correct. And here is a temperature dependent emission spectra for demarc by THC. So this is just in two methyl THF at 77 K, the emission spectra. So we know two methyl THF is very polar, but if we at very low temperature, we see that we have negligible stroke shift. And this negligible stroke shift is because when we habit the main geometry and we excited the molecule, we kept it in a very low temperature, the molecule could not relax. Even the stroke shift is smaller than cyclohexane, which was very non polar. So the idea of relaxed, bent orthogonal is the way we went, we understood. So this is a correct idea. And for triplet, for the second molecule we got two triplet, one was 60 degree in plane, and the one was 30 degree out of plane. So there are two triplet and we are not really sure which one really happens in the excited state. Just one data about the net film study is that if you allow the molecule in the room temperature, if you allow the molecule to relax. If you give enough time, everything will relax and we get emission only from the relaxed geometry. But here if we see is that if we are in low temperature, we don't allow the relaxation. Then we have the same bed here from unrelect geometry, but if we allow enough time in the room temperature, then the molecule gets relaxed completely. So here's a schematic just to say that we have two triplet geometry, two optimized for triplet for our second molecule. But the bench geometry and the two triplet optimized geometry, the energy gap is very high to be 88F. At 90 degree, the energy gap is smaller. And then we have a spin orbit coupling high and then demarcated. So we have two different molecules, two different structures. But when we, for the second molecule we start from a geometry that is not the idea, but if we allow the molecule to relax, it becomes a bit better. So it's very important that we look at this geometry in the ground state in the excited state temperature solvent to understand what really happens in the process. And I hope this gives a good idea about how much relaxation of the system in different environment. And thanks for listening. And thanks to my professor and the primary professor and professor like this man Coleman, the collaborator. Thank you. Thank you. Yeah, it's a very interesting talk. So we have time for maybe one or two quick questions or maybe one question actually do. I see some hands. I don't see any hands but there is a comment in the chat box. Oh, there is a hand. Just give me one second. Yeah, there's a comment in the chat box by under the Muslim dad. Would you like to ask your question. Is this a question or a comment would you like to. Hello. Yeah. Usually spin orbit coupling is also like used to explain the population of triplet from singlet states. So, like what is the driving force mainly for risk that how different it is like is there any magnitude effect which plays a key role. So, for intersystem crossing, we are going to triplet from singlet. Okay, so the energy, so we are going to lower energy from a high energy state for reverse intersystem crossing we're going to higher energy state from low energy state. So the energy that matters, and the spin orbit coupling matters. So the spin orbit coupling is always there and higher you have the coupling high risk that is great. But if the coupling is higher than the probability of triplet population also increases like we've seen heavy atomic effect and. Yes, yes, yes, yes, yes. It's kind of reversible so you have both. Okay, okay. Thank you for selecting the question from Giovanni Bressan. I mean Giovanni, would you like to ask a question. Yes. Hello. Thanks for the talk. I was just curious about the emission spectra because I've noticed that as a function of the solvents. I mean the redshift changes of course but the shape changes if you could go back to that I remember the one as a. Yeah, so in. Cycloxane right you have this sort of double peak structure, which and it's also like where you have the smallest redshift with and here these are normalized so it's harder to I guess like tell if the yield is going up or down either right. I'm not sure. No, I don't know, because it looks to me like that. I mean, Cycloxane is quite known polar so the charge transfer might be quite so I'm assuming that these could be sort of you still have some emission from the donor, you know, you'd like the energy transfer sort of. It might be due to there is a small localized and just transfer character. Yeah, because the more you go to the red the more it loses like features and the more it looks like a charge like a sort of exit flex kind of thing. So, or you don't, but like your, I mean that shape thing doesn't come out of your calculations right. Okay, thanks a lot. Thank you. Thank you, I think that's all we have time for at this point, so I think we should move on. Okay, so let's move on. So in fact, this is the end of this session we're actually going to the last session of the day.