Deazaflavin-based strong reducing agents produced by light
So dear colleagues today is the day of our seminar think this is the last seminar before Christmas and New Year’s vacations and uh today we have uh lecture from Czech Republic Professor radik cibulka he’s graduated from University of chemistry and technology prag in 1996 in the same University he obtained
PhD in 2002 and habilitation in 20 2009 he hand his postdoc in Department of organic chemistry of University of Regensburg in Germany with Professor Kik in 2003 and then after this he started independent scientific career firstly as assistant professor then as associate professor and now since
2017 he is a full professor in Organic Chemistry University of chemistry and Technology Prague his main research interests are heterocyclic chemistry with application of photocatalysis organic catalysis and Redux reactions flavine based Redux and photoactive systems as well as biomatics reactions Professor cibulka was awarded by numerous Awards including prize of
Joseph kavka young chemistry award in organic chemistry from Sigma ald Alfred Bader priz for organic chemistry chemistry Europe f and Rudolf lucash priz from the Czech Chemical Society for excellent results in the field of organic chemistry therefore it’s a pleasure for us to listen your lecture here okay and you can start
It uh Valentine thank you very much for very kind introduction uh my regards from prag to harf and uh ladies and gentlemen I will start with this photo which is on the first slide here and this is photo I did during my visit on 2018 and uh I am really I really believe
And I’m sure that I can do the similar photo very soon and I will visit K again in peace time so uh I would I would like to start with the area which uh I’m focusing with my colleagues in in the lab and it is using light to uh to mediate chemical
Reactions and uh light is something which uh can help us a lot uh doing reactions which are usually not possible in dark and uh for this uh we are using uh special type of compounds which are called flavins and as a Flavin and today I will little bit more focus on the area
Of reductions in principle light can be considered as a chemical Regent and uh it can help to uh to uh to jump the energetic barrier uh when absorbing the light by any component of the reaction and then we can do either asonic reactions with high energetic barrier or what is even
Much more challenging is that we can even jump the energetic barrier in the case of antonic reactions and in such a case we in principle store the energy into chemical bonds and of course nature do it for far well because we know one of the most f famous reactions which is
Photosynthesis where we by using cide and the special system uh we can drive the chemical reactions of CO2 with water to produce CC Bonds in glucose and on this way we are able to store energy about 3,000 kilog per mole and it is really very high energy
Uh in chemistry we can use similarly the energy of light and to pump it into the system and and store it into uh chemical bonds and in principle we are calling such type of uh of reactions photochemistry and when we are using any compound which is which is present in
Catalytic amount in the system them and it is the only the only compound which is able to absorb the light then we are calling it photo redo catalysis and this is the area which was developed within last 20 year and today it is one of the alternative which we can use for our
Organic synthesis and uh how it works uh we are using any dye which absorb the light and this dye is uh excited by the Light usually we can use different type of light we can use UV as well as visible light but I will explain it you later that the visible light is
Advantageous after absorption of light we are producing uh compound which is in excited state and uh the most important principle is that in excited state any molecule is much more reactive in comparison to ground state it means that it became stronger reducing or oxidizing agent and by this way it is able to
Oxidize or reduce this example is for oxidation so it means oxidize any substrate which forms then radical or radical C and this radical cat then reacts with other species to produce our product of course to be catalytic then the Catalyst should be uh should be regenerated in the catalytic cycle by
Any sacrificial Regent or also we can have the catalytic Cycles where we can really use this product to uh regenerate the Catalyst in Principle as I already mentioned we can use the whole Spectrum for the photo Redux catalysis but you can imagine that going to UV light we
Can have photons with very very high energy it is nice from the point of view of exitation on the other hand we have the problem because the energy for example of the light which is uh in Uva area it is the energy which is enough to
To cleave the carbon hogen Bond and this is for example the reason why you cannot store brominated compounds under sunlight because in such a case uh the brominated bromine containing compounds are not stable and you can see formation of bromine within one month area if you have on the bench your brominating compound
And this is the problem because using the very strong UV light it is not selective you can break the bonds you don’t want to break and this is the reason why why photo Redux catalysis today much more prefer to use visible light from 400 to higher wavelength why
Because then we can selectively excite our photocatalyst without uh without problem with itation of other regions and we can selectively provide our catalytic cycle it has also some practical reasons why it is advantageous because we can have that are practical aspects because you can buy Lads LEDs which are not so
Expensive and we can also work in normal glass so it it is not necessary to use silica glass apparatus which are very expensive so we normally are working uh using LEDs and in normal erand M flask or in schlank tube it depends which type of reaction we are
Doing I already mentioned that using light we are producing very strong oxidizing or reducing agent it is uh it is shown here for example if we can have oxidation of compound B with the compound a it means that we should transform this electron to compound a so
It means to this orbital but it is impossible in ground state if it is on this if the levels of uh homo lumo levels are of this energy because it’s uphill and it is not possible but after exitation of a I said for it could be photocatalyst for example we have free
Space here and after that we can have very very uh fast transform of an electron to this area and we have formation of the radical andon which is the case of catalyst and compound B is oxidized this is the principle of using light for formation of strongly strong
Oxidizing species and the reaction is uh can be described by the gips energy of course and it should be uh negative and uh in principle the most important uh value is here is uh energy of reduction or reduction potential in excited state of our photocatalyst which can be easily
Found by measuring s cyclic voltametry so it means the reduction potential on ground state and uh energy of exitation which can be uh found in absorption on and floresent Spectra for example and what we need we need of course that our oxidizing agent is has this excited state Redux chemist Redux
Potential higher than our substrate and the same works for reduction so I will go much quickly so if we reduce C with a we can have this situation but after excitation we now have the possibility that the electron can go to the C and C is then reduced by a in excited state
And in the case of reductions we of course need that our excited state potential of our catalyst is much negative in comparison with our compound so uh in principle uh we can use different types of dyes for our our photocatalysis and many of them are commercially available you can see the
Ranium idium compounds which are pretty much stable and also very strong reducing or oxidizing agent depending on substitution uh we can have acridinium salt we can have aoine which was one of the first photocatalyst used in photo Redux catalysis and uh originally it was used for photo
Imaging and uh this Catalyst which was used for for which is used for reductions and it was really uh found specially for reductive photo Redux catalysis but if you can see here they are no these catalysts are not so uh not so cheap uh with the exception of aoine
Which is produced in high amount and this is also one reason why the chemists are looking for new and new photocatalysts uh which uh especially among uh organic molecules can be much more cheaper in comparison for example with these uh complexes and uh of course the other motivation and maybe the most important
Motivation is to have much stronger reducing or much stronger oxidizing agents and uh in our laboratory we are uh focusing on the Catalyst which are derived from vitamin B2 from riboflavine which is known to be uh co-actor which is uh responsible for electron reductions either one electron or two
Electron reductive processes in many different flavo enzymes we have in principle more than 1,000 flavo enzymes in organisms and you can see that the flavine can form either radical anion or the anion species and of course in oxidized form it can work as a reducing
Or in reduced form uh it can work as a reducing agent so there is oxidant and there is reductant and moreover the flavines are very nice species which are uh which are yellow the this is also the name flavine which comes from flavus yellow and uh this is the this yellow
Orange color which is which comes from absorption and you can see this also slightly greenish compound because of fluoresence and the fluoresence appearing here looks or or shows us that flys probably can be also used in photo Redux catalysis and this is what we are doing we are playing with the structure
Of flavine for example we can replace this nitrogen to carbon to have DEA flying we can uh change the configuration here of these double bonds to have alazine as a as a other derivative or we can introduce here even aering to have quary uh it means positively charged
Flavines which are also very good uh oxidizing agents and uh in principle we are use looking for new Flavin derivatives and of course for their new applications in photo Redux catalysis uh I will talk today mainly about reductions but I will start with oxida oxidative chemistry and the reason
Is that the flavines were from the beginning considered as very strong oxidizing agent in an excited state but uh when we are consider the flavine as a oxidizing agent you can see here Redux potential which is really much lower than for example substrate which can be called as a benzil alcohol and oxidation
Of benzil alcohols this is something one of the oldest application of Flavin in photo Redux catalysis but you can see if you count this gyps energy it is really very very positive so it means that the flavine in ground state is not able to oxidize this this uh param oxy benzil
Alcohol but after excitation we have the species which has much more positive Redux potential much higher than this partoy benzil alcohol and this spe species can really oxidize this to form radical C which can farther react to alahi so we can use really the flavine as a oxidizing agent which is able to
Oxidize Benzel alcohol to alide in this reaction flavine is reduced to reduce form and this form is reoxidized by oxygen so in principle we can use Flavin in catalytic amount and it is cat list of oxidation of this benzil alcohol by oxygen uh to form hydrogen peroxide and our alahi as the
Only products but you can see that the that this oxidant is not so strong to oxidize for example this species but it was shown before by fukuzumi or by Robert WF that you can introduce here the Scandium species which is even much stronger oxidizing agent and you can oxidize this this and also
This in our approach we wanted to to work without any metal and this was the reason why we not introduced the metal to and to have the flavine as a liant but we tried to introduce positive charge here even in ground state we have now very strong or relatively strong
Oxidising agent but not still so strong to oxidize these species but after exitation with uh with violet or blue light we have extremely strong oxidizing agent which is really able to oxidize everything and these applications can be shown here for example using five mol% of this Catalyst 450 nanometers SL
Acetonitrile as a solvent and a little bit U little bit more elevated temperature we can oxidize benzil alcohol to corresponding acid or even methyl group to corresponding acid or methylene group to corresponding Ketone and you can see here that each reaction works very well uh with the except ction
Of the Rea of oxidation of compounds having here very negative electron withd group and for this reason we need little bit improve the conditions to have carboxilic acid in the system so I introduced flavines as a very strong oxidizing species but now uh I will speak about reductive chemistry
And it was maybe 10 years ago when we we were talk about flavines as a photocatalyst also with burghard Kik and both we had opinion that uh Flavin probably will be much more suitable for reductions than for oxidations and um we have also one parallel in in the nature where the
Flavin are working as a strong uh uh reducing agent and this is shown here uh flavines are known that they are working in in photo liasis uh as a compounds responsible to cleave this cyclobutane skelet back to uh to timin or uril Moes the problem is that the timin and aasil
In our DNA after irradiation with UV light uh forms the cyclobutanes and such such DNA is not functional anymore and but uh for example flavors have the enzyme which is called phoas and in this enzyme the flavine is responsible for back cleavage and restoration of function of these en
Enzymes and the principle is here the principle can be described uh that the flavine is reduced we have reduced flavine which is irradiated and in excited state it’s very strong reducing agent producing this radical and then there is a Cascade of reactions going to free uril or free timin and the
Mechanism of this was uh very investigated by Sankar which was awarded by Nobel Prize few years ago ago by this founding and I will go go back to this slide um when I would like to explain why the reductive catalysis and for which reactions are the reductive catalysis
Important and of course we have plenty reductions in organic chemistry and many of them are done also by very strong reducing agent like like alkaline metals and so on so on and one of aims of chemists is to generate FL fenel radical going from any aromatic species by one electron
Reduction and uh this is very helpful because if we have fenel radical it can react with different type of species for example with double bond Veer with heterocycles and with other compounds to produce novel CC Bond CC Bond here to heterocycle C Boron Bond if we are reacting with boronic compounds or even
We can reduce this aromatic species to form the free Benzene ring and uh this can be helpful with when we control such type of reactions but the problem is that these compounds are sometimes of very negative reduction ction potential you can compare it of course you probably know very nice
Applications of diazonium salts diazonium salts are known to known to produce some radicals and uh some types of re of uh of reactions which are in principle uh responsible for example for production of chloro Benzene but uh producing diazonium salt or you can see iodonium salt or these compounds uh
Are not so easy and in principle commercially available compounds are much more from the area of hogen benzines or hogen containing uh aromatic compounds and the problem is if you see that really reduction potentials of such compounds are very very very very negative and it’s very difficult to
Reduce them and we have in principle several possibilities how to do that when reductive photocatalysis started we use single Photon photo reductions what it means it means that the photocatalyst is excited in excited state is able to reduce uh the this hogen Benzene to form this radical anion and the photocatalyst
Is then regenerated by by any sacrificial region such a such a radical anion is then very easily producing helide and corresponding radical but you can see that this reaction uh ends here somewhere about minus 2.2 volts and we have no stronger uh phoc Catalyst even uh after excitation
The second principle found by bulard kenic is based on consecutive photo electron transfer photo reductions so it means that we use two photons the first one is to produce the radical anion and this radical anion is excited again to form excited radical anion and these particles are very very strong reducing
Agent and we can compare reductions uh Power with sodium and even with lithium uh sometimes we can replace this part also by electrochemistry and we have in literature some uh applications of combination of electrochemistry and photochemistry and when I can uh tell something about the very strong reducing
Agent so it is one radical which is formed from this acridinium and very uh recently published this benzo or indor tile forming this anion which is extremely strong after excitation so what about flavins uh we started about to S to think about using riboflavine tetraacetate and its derivatives but we
We thought about that maybe it would be much better to go towards chemistry of deazaflavins you can compare the deazaflavin had much more negative reduction potentials so in principle they can be much more suitable for reductions in comparison with this flavine and we started with this and uh
Studing the reductive properties of this compound we found that it easily forms this radical or radical anion depending on the on the amount of protons in the system or this reduced agents but especially this radical was surprisingly relatively stable when fenel ring was here you can see this is oxidized form
Then it forms this radical which also absorb visible light around 400 nanometers it can be seen here when we apply potential about one minus 1 1.4 volts so it means this reduction potential that is the formation of this radical and this radical was found that it is really very strong reducing agent
With potential about minus 3.3 and uh we apply this Catalyst for reduction of such difficult substrate like mettoy bromo Benzene so bromo anol which can be reduced by this Catalyst and uh uh we found that uh when we have this original catalyst so it mean this with fenel ring we can have
Very nice uh very nice production of the reduced species which seems that we are able to reduce this compound uh with fenel ring it is much better than with isopropyl and much better when this hydrogen is here the reason is the stability of the radical being here and the mechanism uh found
Was that the Flyin is excited then it takes an electron from the sacrificial reducing agent this is any amine for example diare and this amine reacts or or this Ian put the electron here to form the radical anion flavine radical anion is excited again and it excited species it’s such strong
As I describe before being able to reduce this uh Arial uh halides and uh this was very exciting finding that such flavins are very strong but we found one problem in the system and it was that this fluing radical in the presence of DEA which was
Formed this radical CES uh form such a radical pairs of course this is negatively charged this is positively charged and this per in excited states can very easily uh undergo back electron transfer from flying back to I mean and uh we are forming here this starting and it decreases the yield of our
Photocatalytic system and it was the reason why we started to to look why it is the true and we found that the problem is that this this Catalyst has relatively low inter system Crossing so it means transformation from singlet to Triplet excited state and with the aim to increase this interstem
Crossing yield we introduce heavy atom which is known to support this inter system Crossing usually and you can see uh it was very very successful having these two Catalyst the problem of this one was that the bromine was directly on this fenel ring and it means that after
Exitation we lose the bromine Atom from the system and it was not so active anymore so that was the reason why we have chosen this Catalyst as the best one and you can see that we really were able to reduce very very very NE very difficult substrates for example chloro
Anol also the compound with two methoxy groups also compound with three mexy groups or this derivatives with relatively good yields and it works also prep comparatively you can do it in relatively high amounts so uh it was story about dehalogenation which is reaction which used usually as a model reaction to show
Reductive properties of the system and uh we also tried to find application of our system uh and uh one application we found between the protection of compounds which was uh studied by with by Tanya and also by Eva and um this tsil group is usually
Used as a as a good uh protecting group to a means and uh today also the ORS are using those this sulon group containing Tri floral group or even per floro alkal groups in general these these protecting groups are very helpful it helps us also in the synthesis because this very
Strongly electron withdrawing groups for example a low introduction of any uh alkal group to this position and it is very easy to to work with such derivatives but the general problem is how to remove the protecting group and it is usually done under very harsh conditions by reductive conditions or
Harsh conditions by acidbase hydrolysis and it is the problem for the rest of the molecule even worse situation is here with trioral or Trio alal suil groups which are really much more even much more difficult to remove than this toil group there are some uh novel uh ways
How to De protect it for example using this acridinium salt which I already showed you as a strong reducing agent but it is it was tested only for tosel derivatives or using this very very electron Rich compounds and to use it for for de protection of this trif group
Of this Tri florom metal containing group but still there is uh no any general group or method which can be used for all such sual compounds and for that we try to to use our Flavin derivatives this is what which you already know but we thought about that
Maybe we can go from this DEA flavine to DEA alazine which is even much more stronger reducing agent even in ground state and we really found that this compound is extremely strong uh reducing agent helpful in this chemistry you can see we have 8% of the Catalyst 400 nanometers
Basic conditions and DEA which is used as a source of electrons and you can really cleave the nitrogen sulfur Bond it means deprotect I mean in the case of analin in the case of analin with different groups uh in the case of secondary or tertiary analin also in the case of phenols and
What is really challenging that we can do that also with trifil groups or even Nona groups which which means that it is this per floal group and the mechanism is similar as for dehalogenations so it means that the catalysts in excited state in the form of radical anion which is form using the
Sacrificial uh donor is responsible for one electron reduction of this very uh very uh difficult with which is the species which is very difficult to reduce and this radical anion then produces the amine what is important that the other product is this sufin Nate it means the
Salt of sulfinic acid and I will show you in the next slide that it is very important species because what we have found that we can even uh to set the conditions that we can do trifle derivative removal or we can either to remove the alkal
Group from this uh system so then from this uh protected SE secondary I mean we are producing primary anelons and how it works I already showed you this catalytic cycle that we are producing the amine and this alkal sulfinate but in the case when we have
This Tri so we were talk about this very important species which is this alkal sulfinate and this alkal sulfinate then can be oxidized to by the flavine again to form this radical and this Radical take an electron here to form this radical and finally we can have this imum species which is which is uh then um hydrated and to form the final product I talk about that we can form this anine and it is the product of the reaction so uh the catalytic Cy dirty
I think that there is then finishing this our catalytic cycle and the S SO2 is something which is used to reoxidize this radical to to to restore our Catalyst I showed you that the flavor can be very strong oxidizing agent and very strong reducing agent and
What about to put it together and to you utilize both of them uh for any uh practical application and we thought about one practical application and it is chemos selective oxidation this uh this is chos selective oxidation because we know that some chemistry uh is not so
Easy even if we have many different oxidising agent so it means that oxidizing alcohol to alide or acid yeah it looks nicely uh but you should have very chemos selective systems we have some of them we have also chemoselective system for uh the most difficult task is to have two different oxidisable
Species in the system so it means to oxidize for example only alcohol and not to oxidize sulfide and the same here for example to oxidize only alcohol and not to oxidize the methylene group and uh one possibility is to use photor Redux catalysis but the problem of oxidizing
Photo Redux catalysis is that you need to have sacrificial oxidant and sacrificial oxidant in photoed catalysis is usually oxygen or any even stronger oxidizing agent which are producing very reactive species like singlet oxygen hydrogen peroxide or super oxide and these are responsible for many different undesired oxidations
So we thought about to not to use sacrificial oxidant in the system and and one possible solving the problem is known in the literature and it is to use any Catalyst usually as a for example Cobalt complexes which are able to be reoxidized with proton to form the
Hydrogen so it means hydrogen coupled oxidizing reactions but we thought about another way to use solvent for re oxidations and we found this uh we found this system by the way that we tried to construct Catalyst which will be either both strong oxidizing and strong reducing agent I showed you some couple
Minutes ago that this flavinium salt can be very strong oxidising agent with this potential I also showed you that flavins or DEA flavins can be very strong reduc in agent doing this chemistry so we prepared or think thought about such a hibrid which is DEA and also flavinium
Salt and we try to test them in both oxidations and reductions and we found very interesting uh property properties of this Catalyst we studied this oxidation so it means secondary alcohol goes to the Ketone and this in the presence of this new Catalyst which has carbon here and
Quary Centrum here working on the oxygen uh allowed us to prepare this Ketone under with quantitative field this is what we expected but unexpected result was found when we did the reaction under argon it means that we have no oxygen in there and question was what is oxid sacrificial oxidising agent
Here very probably acetonitrile which was used here as a solvent we tested other solvents like acetone which has very little oxidizing properties the meyl sulfoxide little bit more oxidizing properties and you see that the results were not so nice as in the case of aceton trial and this was the reason
When we started to use aceton trial as oxidizing or means to use the solvent as sacrificial oxidizing agent and we studied the mechanism if it is true because to reduce acetonitrile is really not so easy because it has very low very negative reduction potential so this is the flavinium salt with nice Spectrum
Absorption around 400 it is excited then we studied if this compound is able to oxidize our substrate it’s true we use fluorescent quenching experiment to show that this species in excited state is able oxidize this uh alcohol so it was the first step the second step we identify this
Radical by ep V very nice measurement with experimental calculated Spectrum which were the same and also we try to generate this radical using sacrificial uh sacrificial reducing agent you can see that it was formed here and the same result we obtain by electrochemistry so it means really we
Have this radical which can be excited by 400 you can see that it abs abbed here and it’s in excited state it can work as a strong reducing agent probably it is able to reduce acetonide trial to form this solvated electron which is in equilibria with the diare radical an i
This is known that these species can be monitored by UV uh or maybe maybe better set IR spectroscopy and you can see it here that this uh electron which is Sol weighted an aceton is visible here and it corresponds pretty nicely with the data these are these dots from the
Literature so we found that really we are producing solvated electron which is then forming this radical anion and after hydrolysis there is production of AET alide which we found and also detected using hydrain so we found completely new procedure which is very chemos selective and which uses acetonitrile as the only
Uh sacrificial oxidon so it means we need only Catalyst light and solvent not oxygen uh when we compared experiment under oxygen and under argon you can see here nice chemos selectivity because under oxygen we are oxidizing both alcohol and sulfur but under argon that is only the dihydro dihydrogenation reaction and not
This oxidation because we have no oxygen in the system so under argon we have pretty nice chemos selectivity very similarly under oxygen we can observe both oxidation of alcohol and methylene group to C but under argon we have only oxidation of alcohol to the Ketone and the same here we can see nice
Selectivity because under argon we can have only oxidation to alahh and not to not to cor carboxilic acid which is known to be observed under oxygen so you can see this very nice application of flavines and we can tell as and we can conclude that really Flavin can be very strong oxidizing
Agent and also very strong reducing agent and we found many interesting synthetic applications of such uh reductive species in organic chemistry we also found that we can have the species which is really both oxidizing and reducing and uh for the future we are thinking not only to combine photo
Catalysis in oxidative and reductive chemistry but also we can use flavines as organocatalyst and biocatalyst of course because uh you can use also enzymes directly as uh as have strong oxidizing and Str strong reducing agents at the end of of my talk I would like to thank
All people for very hard work uh especially when we are talking about reductive chemistry is a Tanya and IA and uh when we are talking about the chemistry oxidation comb combination of oxidations and reductions it is Robert uh everything is covered by Eva and also with other people are involved
In our uh very nice work about uh flavine catalysis I would like to thank also our our Co collaborations both in Czech Republic as well as in abroad I would like to thank all Grant agencies for financial support and finally I would like to thank you for nice uh for
Great attention and thank you very much again for invitation uh thank you very much uh Professor tulka for your lecture and sorry for this accident during your lecture it was huged by Russia Federation to prevent even scientific events in Ukraine uh unfortunately we have only 10 participants now you now yeah we lost
Some of them of yeah but you mean you know it looks that it shows that the situation is not normal yeah that’s unfortunately yeah but maybe somebody from from our participants uh have a questions to our lecturer concerning this chemistry and yeah okay I have maybe some
Questions to you uh uh first of all uh it’s about um real application preparative application and maybe semi-industrial or even industrial applications of such interesting processes what do you can to to say about this uh in principle it is possible but we expect a relatively long way to to to go there
Because for we can tell about industrial application you need that your Catalyst will be very very very stable so it means that you can use it uh for many times and this is relatively problem with flavines and generally with all organic photocatalyst because uh they are relatively
Non-stable uh on the other hand we can tell you that some of our derivatives are much more stable than the derivatives uh at the beginning of our work work with flavins so it means that for example for some uh small not industrial but maybe some relatively small amount application like working
With tens or hundreds of grams I can imagine so it means for example in pharmaceutical uh industry in in uh in in synthesis of upas or something like that uh I can imagine that such uh an application can be found yeah okay and exactly about pharmaceutical in some in
Some cases you showed us yields of your compounds only NMR or hlc yield what about um real yield and purity of your compounds after these um protes okay uh yeah I I showed it uh not to be so long with uh explanations but uh in general uh especially for for
Example for these de protection reactions uh we know that we can isolate our products in very high Purity in good to some cases excellent yelds and the same is also for our chemos selective oxidations so of course for comparison we are using usually NMR yields but in
All cases we also done uh or we also did uh the preparative experiments showing that it is possible to use these applications yeah okay and in purity of your compounds is rather High yeah yeah yeah yeah okay so and my last question uh do you have other types of organic
Photocatalysis uh with such high uh potential for reduction as flavines uh as I showed you before there is this acridinium salt yes I remember really yeah which is really very strong and uh yeah uh when I start as a organic synthetic chemist to do something with reductive
Chemistry so I will try this acum salt then our flavine and then one of these uh of this cyano benzene derivatives these are very strong and already well investigated M okay thank you so dear colleagues maybe somebody has question as well nobody okay thank you very much
Again for your time for your lecture and have a nice evening today thank you very much and uh especially I wish you very noisy and uh good evening and all Christmas time in in har thank you thank you so goodbye Valentin bye I hope we will see yeah yeah yeah yes me too