Chapter 222: Experimental failure is the main theme of scientific research

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Xu Qiu was very interested in introducing the cyano group. He had investigated the knowledge of cyanide before, and it happened to be used at this time.
"Inorganic cyanide, such as sodium cyanide, potassium cyanide and other inorganic salts, is indeed very toxic, the kind that can belch with a little dose.
However, for cyano groups, organic cyanides are used, which are relatively less toxic. For example, the commonly used acetonitrile solvent is only moderately toxic.
The principle of cyanide poisoning is that free cyanide ions can inhibit the activity of a variety of enzymes in cells in the body, causing cells to suffocate and die due to hypoxia. Organic cyanide dissociates into cyanide ions in the body in a small amount.
Nevertheless, if you directly contact or inhale organic cyanide vapors in large amounts, there is still a great danger, including the introduction of fluorine atoms, and the use of fluorine reagents.
In short, I'm just a suggestion, and you need to see your own thoughts on how to do it. "
"Okay, I'll think about it again," Chen Wanqing nodded, "Today, let's synthesize according to the existing design of C4 molecule."
A502 laboratory.
The DEBUFF that had reduced work efficiency has disappeared, and Xu Qiu is full of enthusiasm, preparing glass instruments, magnetic stirrers and other necessary equipment.
The two improvement paths he chose were fused cyclization and the introduction of heteroatoms-selenium.
For the newly synthesized 3D-PDI molecules, the central core unit and the surrounding PDI molecules are connected by a single carbon-carbon bond.
The carbon-carbon single bond can rotate, so the molecular structure is not fixed, forming a variety of molecular conformations, which will destroy the conjugated structure of the entire molecule, which is not conducive to the charge transport within the molecule.
The fusion ring is to connect the core unit and the surrounding PDI molecules through "two" carbon-carbon single bonds, which can stabilize the molecular conformation and improve the conjugation of the molecule.
For example, if two people hold hands, just holding one hand, then it is very convenient to move around, and many postures can be unlocked;
But if both hands are pulled up, the posture of the two people will be restricted, and it will be very difficult to think of any tricks.
This idea of ​​fused ring is essentially imitating the spherical structure of fullerene C-60.
The entire molecule of C-60 is a fused ring structure, and the conjugated system on the surface of the sphere is connected as a whole, and the charge transport ability is very strong.
Another way to introduce selenium atoms is Xu Qiu's idea based on the existing literature, which can be regarded as new wine in old bottles.
In organic photovoltaic materials, the introduction of sulfur, selenium, fluorine and other elements may improve the photoelectric performance of the material. It is difficult to introduce fluorine atoms here, so he finally chose selenium.
As for the specific principle of the improvement of optoelectronic performance, there is no unified statement in the academic circles.
Many questions are unanswered at this stage, but it does not prevent people from applying them.
...
Start the experiment.
The first reaction is the photocyclization of PDI3-B-5.
The raw material used is PDI3-B-5, the iodine element is used as the catalyst, the solvent is toluene, the conditions are normal temperature, light, and the reaction time is 24 hours.
Firstly, toluene is redistilled, and then the remaining tens of milligrams of PDI3-B-5 material is added to the reaction flask.
The reaction of small molecules does not require a high amount of solvent, so Xu Qiu added 15 ml of re-vaporized toluene to the reaction flask to dissolve the raw materials.
Next, add 1 mg of elemental iodine.
Finally, when the device is irradiated by high-pressure mercury lamps, many street lamps on the street are high-pressure mercury lamps, which have the advantages of low cost, high light efficiency, long life, and power saving.
This reaction should be the easiest reaction since Xu Qiu did the synthesis experiment. It took almost no effort and was completed, and there was no danger.
The only drawback is that the reaction time is a little longer, and it takes a whole day to wait.
The second reaction is the selenization reaction of PDI3-B-6, which is carried out in two steps. The first step is to introduce a nitro group at the bay position of the PDI molecule, and the second step replaces the nitro group with a selenium atom.
In the first step of the reaction, the raw materials are PDI3-B-6 and concentrated nitric acid, the solvent is dichloromethane, the condition is normal temperature, and the reaction time is 8 hours.
This time, instead of re-distilling the solvent, add the weighed PDI3-B-6 material and 10 ml of dichloromethane directly into the reaction flask.
Then, dissolve 3 ml of fuming nitric acid in 5 ml of dichloromethane. The so-called fuming nitric acid is a liquid with a concentration of nitric acid between 90% and 97.5%, which is reddish-brown due to the dissolved nitrogen dioxide and is corrosive. Very strong and can be used as rocket fuel.
Because of the high risk of fuming nitric acid, Xu Qiu deliberately put on an extra layer of gloves when taking it, and pulled the glass of the fume hood to the bottom before unscrewing the cap of the reagent bottle.
Even so, there was still a hint of sourness leaking out.
After the prepared fuming nitric acid was dissolved, Xu Qiu slowly dropped the solution into the reaction flask, dripping it drop by drop, not all of it was added, only 0.3 ml was added.
Finally, add a magnetic stir bar and stir at room temperature.
The two reactions were good, and it only took less than an hour.
The reaction route was designed by Xu Qiu himself, and the reaction conditions were summarized based on the literature.
Although most organic reactions have more general reaction conditions in the textbooks, the guidance of the literature is very important for specific and professional molecules, such as the synthesis of PDI.
If there is no literature reference, it may take three or five days, or even a week or two, to explore the conditions.
However, his molecular structure is only similar to the literature, not exactly the same.
Therefore, Xu Qiu had no idea whether he could get the desired result in the end.
As for the power of the system, such as the simulation laboratory I, it is not very suitable.
Currently he has Simulated Lab II, and Simulated Lab I is rarely used.
The main advantage of the latter is that it can be accelerated, and like this kind of reaction time of 24 hours, it is forcibly spent 2400 points to accelerate to verify the feasibility and the price is too low;
If the reaction time is relatively short, there is no need to speed up, because the reaction also has a fixed time cost, so it is better to invest in reality.
The only advantage left by the simulation laboratory I may be that it does not need to consume materials and can save experiment costs.
But materials such as PDI are very cheap and can be made at will.
Saving money or something doesn't exist.
After casting two responses, Xu Qiu wandered around in the laboratory for a while, and saw that the school sister and the school girl didn't seem to need his help, so he returned to the office.
...
Time flies and it comes to night.
Because of the big light bulb like senior sister, Xu Qiu and Han Jiaying are not too presumptuous in the office, and they spend most of their free time writing reviews seriously.
At present, Xu Qiu's progress is very fast. He has completed the second part of the PDI content that he is responsible for, and is integrating with the A-D-A part of the school sister.
The school girl's words, according to her, were a little bit close, and she didn't know the truth or not.
The first step of the second reaction is the time for the nitration reaction.
Xu Qiu went to the laboratory for post-reaction processing.
He was dumbfounded after seeing the results of the click board.
One, two, three... sample points.
"Fuck."
"Brother, what's the matter?"
"The experiment failed."
"Do you need my help?"
"No, you continue to cross the pillar."
"Okay."
Xu Qiu is calm, he knows that experiment failure is the main theme of scientific research.
It's just such a taste, he hasn't tasted it for a long time, and he really misses it.
‘Now that the facts have happened, the most important thing is to find the reason for the failure of the experiment, and then to improve the experimental route or method. ’
‘So, where is the problem? ’
Xu Qiu shrank his nose and smelled the seemingly absent solvent smell in the air.
This is a unique taste of organic laboratories, because a large amount of opened solvent is stored, even if there is a gasket on the bottle cap, a small amount of solvent will escape from the gap.
Therefore, the ventilation of the laboratory is very necessary, otherwise chronic poisoning is inevitable in such an environment.
Even when wearing a gas mask, solvent vapor can still penetrate into the human body through the surface of the skin.
The laboratory is not a place for thinking. Xu Qiu and the school girl greeted them and returned to the office.
Chen Wanqing was chasing the drama with headphones on. She looked up at Xu Qiu, then lowered her head and locked her eyes on the computer screen again.
Xu Qiu washed his hands, returned to his desk, turned on the computer, checked the synthetic route of his reaction, and began to analyze:
The conditions for nitration substitution with fuming nitric acid are already very violent. It stands to reason that PDI molecules should not resist the attack of nitric acid molecules, and it is easy to obtain trinitro substituted products.
Each PDI molecule has two reaction sites at bay positions, because they are on the same side, only one nitro group can be added, even if...
No, it is not two reaction sites, but three, because the central benzene ring and the side PDI molecules are connected by a single bond, which means that there is an additional Bay site reaction site on the other side.
For the three reaction sites, the reaction site on the outer side has a high chance of being substituted. Because of the steric hindrance on the inner side, the reaction activity is not high, but not low, that is, three, four, five, and six substitutions may be formed.
It turns out that with so many possible products, it's no wonder that there will be a row of sample points on the dot board.
How to improve it?
Either change the nitration reaction and replace it with other groups, or adjust the conditions of the nitration reaction to reduce the reactivity of the central high steric hindrance area, or reduce the reaction sites of each PDI molecule to two.
The third option, UU reading www.uukanshu.com seems to... just fit the halo reaction.
If you perform photocyclization first, change the center of the molecule to a fused ring connection, and then perform nitration, you don't have to worry about the inner reaction site, because it has disappeared.
Hey, it is a pity that this pot of raw materials is used.
After finding the reason, Xu Qiu returned to the laboratory.
First, deal with the failed reaction, and then look at another pot, the photocyclization reaction catalyzed by iodine.
He checked the board and found that the raw material points are already relatively shallow. Although there are two or three shallow sample points, the color of the main product points is relatively dark, which means that the current yield has almost exceeded 50%.
With a high probability of success, Xu Qiu was determined.
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