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Zhang Jiang's laboratory.

Han Jiaying turned on the liquid chromatograph to purify the product mixed yesterday, while Chen Wanqing went to the fume hood to handle the reaction.

Xu Qiu also began to prepare for the next step—modification of PDI molecules.

Before receiving the JACS review, his idea was to synthesize simple PDI molecules, and then do 3D-PDI directly, and publish this idea as soon as possible.

Now that other people have proposed the concept of 3D-PDI, there is no need to be so anxious.

He intends to proceed step by step, and first synthesize several known high-performance PDI materials, mainly twisted and bridged PDI dimers.

Even if these materials are not used now, they will have the opportunity to be used in the future. They can be stored to expand the breadth of materials in the laboratory and build a material library, including the sample samples that the photoelectric company sells today, which is also used to enrich this material. Library.

After that, every time a new material is developed, it can be matched with the materials in the material library in the simulation laboratory II to build binary or even multi-element battery devices and test their performance.

Moreover, this can be regarded as re-walking the synthesis path of the predecessors, and can further accumulate his synthesis experience.

PDI dimer, whether it is twisted or bridged, the main design idea is to make a twist angle between two PDI molecules through dimerization, thereby inhibiting the crystallinity of the entire dimer molecule and improving spin coating. The morphology of the film afterward.

The difference is that the twisted type is to directly connect two PDI molecules, while the bridging type is to add an additional "bridge" between the two PDI molecules. The so-called bridge is a small conjugated structural unit, such as thiophene, vinyl some type of.

But it is not so easy to connect two PDI molecules obediently, and direct reaction is obviously not possible.

Firstly, the molecular structure of PDI needs to be modified. A common method is to replace a hydrogen atom on the molecule with a bromine atom to obtain a monosubstituted PDI-Br molecule.

Then directly react two PDI-Br molecules, or introduce a bridging molecule to obtain a twisted or bridging dimer.

Theoretically, PDI+Br2→PDI-Br+HBr, in one step.

There will actually be problems.

A single PDI molecule has a total of 8 hydrogen atoms. Because the molecule is symmetrical, there are two hydrogen atoms in different chemical environments, which are divided into in-situ and bay-position, each with 4 hydrogen atoms. The hydrogen atoms in the same chemical environment can be considered to be in the are equivalent in reactivity.

Relatively speaking, the bay position, that is, the four hydrogen atoms near the center of the molecule are more chemically active and are more likely to be replaced when a bromine substitution reaction occurs.

If the reaction conditions are well controlled, the hydrogen atoms in situ hardly participate in chemical reactions.

But only 4 in situ can be excluded.

There are 4 hydrogen atoms on the b position, when the bromine substitution reaction takes place, it is possible to produce 0, 1, 2, 3, 4 substituted products.

Because there are relevant literature published, there is an answer to this question. The key lies in how Xu Qiu chooses.

One method is to directly synthesize according to "2PDI+Br2→2PDI-Br", and then use the column method to screen out PDI-Br.

The advantage of this method is obvious, it is simple and rude, and it can be done in one step. The disadvantages are also obvious. The post-processing may be more painful, and the yield is worrying. If it can reach 50%, it will burn high.

Another method is to introduce a nitro group at the PDI position first, and then reduce the nitro group to an amino group. This amino group can simultaneously eat two hydrogen atoms on one side, and then connect to the nitrogen atom of the amino group. An alkyl side chain, and finally a bromine substitution reaction.

The disadvantage of this method is obvious, and the reaction steps increase by three steps...

The advantages are not obvious, maybe the yield will increase, maybe not, and there may be some hidden advantages.

After some trade-offs, Xu Qiu chose the first method.

In fact, it is not easy to react to the third and fourth substitutions in such a direct and reckless way.

Because when the PDI molecule is replaced by a bromine, the chemical environment of the hydrogen atoms on the other three positions changes, and the position of the hydrogen atom that is most likely to react changes to the para position with the bromine substitution position, or the distance The farthest bay position of the monobromine substitution position.

Therefore, the products obtained are mainly mono- and di-bromo-substituted products, and unreacted raw materials.

Moreover, the dibromo-substituted PDI is not useless. For example, in the future, it can undergo a Stille coupling reaction with the di-substituted trimethyltin to synthesize PDI polymer materials.

...

Start preparing the reaction.

Three reactions, the reaction raw materials are PDI molecule and bromine element purified yesterday, the solvent is methylene chloride, and the reaction is at room temperature, and the target product is a monosubstituted PDI-Br molecule.

Xu Qiu carefully took out the brown bottle containing liquid bromine from the medicine cabinet, and then transferred it to the fume hood.

Then, weigh about 500 mg of PDI molecules of PDI, put it into a reaction bottle with a volume of 50 ml, add 20 ml of methylene chloride as a reaction solvent, and put a polytetrafluoroethylene shuttle-shaped magnetic stirring bar.

The last step is to add liquid bromine equivalent to the PDI molecule.

Liquid bromine is the only non-metallic element that is liquid at room temperature. It is volatile, toxic, and corrosive, so it can only be measured quickly and roughly.

In addition, its density is higher than that of water, so it should be sealed with water above the liquid bromine when it is stored. The liquid bromine will be divided into three layers, the bottom layer is liquid bromine, and the middle layer is bromine water, which also contains hypobromous acid and bromine. Hydrogen, the upper layer is water.

Xu Qiu pulled the glass of the fume hood to the bottom, reached in, carefully unscrewed the cap of the liquid bromine reagent bottle, inserted a disposable dropper into the bottom of the reagent bottle to absorb red and black liquid bromine, and then quickly transferred it to the reaction chamber. inside the bottle.

After the red-black liquid touches the bright red liquid below the reaction bottle, it quickly blooms, and the bottle is filled with dark reddish-brown bromine vapor.

Xu Qiu quickly plugged the reaction bottle with a glass stopper. There are carbon-carbon double bonds in the rubber, which will react with bromine, so rubber stoppers cannot be used.

Afterwards, he added liquid bromine to the other two reaction containers in turn, then capped the liquid bromine reagent bottle, disposed of the experimental garbage with liquid bromine remaining, and started stirring.

'The reaction is getting more and more dangerous. ’ Sighing secretly, Xu Qiu pressed the stopwatch and started timing. The reaction time should not be too long, and the reaction should be turned off on time after 2 hours.

‘I used 10% of the product at one time to test the water, and I hope it doesn’t fail. '

...

Xu Qiu looked around, Chen Wanqing was not in the laboratory, she should have returned to the office, there was no reaction in her fume hood.

Han Jiaying was in the fume hood on the other side, passing the column while rotating simultaneously.

Xu Qiu walked towards the school girl, "You're quite capable, and you can do it with one mind."

"Hey," Han Jiaying turned around and said, "Brother, you're here, how's your reaction?"

"I have voted for the bromine substitution reactions of the three products, and you can vote for your product later." Xu Qiu stood beside her.

"Okay," Han Jiaying pointed to the rotary steamer, "Come and help me, it's very stressful to operate two devices at the same time."

"Okay, then I'll help you watch the revolving steam." Xu Qiu nodded.

"Phew...you're saved." She hurried back to the liquid chromatograph.

The PE cup over there was almost full, so she pressed pause, quickly replaced it with a new PE cup, and continued to receive the liquid.

'Pretty skilled. ’ Xu Qiu thought for a while and asked, "By the way, do you know what happened to senior sister Chen Wanqing? I think her reactions have stopped. I was too busy submitting responses just now and didn't pay attention to her situation."

"I'm not too sure about the specific situation. She came here just now to order two boards, and then ran away without saying a word." Han Jiaying tilted her head, and then she smiled unkindly, "But I guess, She probably failed the experiment and was so angry that she shut herself up."

"That's it, I'll go and have a look." Xu Qiu glanced at the rotary evaporator, seeing that there was not much solution in the eggplant-shaped bottle, and it was running smoothly and relatively safe, so he walked towards the laboratory bench.

This laboratory bench is specially used for spotting and testing, and there are two silicone plates on it, which should be the plates that Chen Wanqing ordered before.

A hand-held ultraviolet lamp is connected to the socket next to it, and it is in a standby state.

Xu Qiu picked up the ultraviolet lamp, turned on the switch, and irradiated the two silicone plates separately.

The above sample points are densely packed, one of them has at least seven or eight points, and some of them overlap each other. If you draw a vertical line, it looks like a candied haws; the other one is slightly better, but there are also five or six points. .

"I guess you guessed it right. I can't bear to look at the results of her tricks." Xu Qiu put down the ultraviolet light and returned to the rotary evaporator.

"Are there many sample points?" Han Jiaying paused, "Three, four?"

"Not only, at least five or six," Xu Qiu sighed, "Even if the obtained product is separated by liquid chromatography, it is difficult to determine which sample is the required substance. In short, the gods are hard to save, either because of her operational errors, or because of her experimental design problems."

"Didn't I show you and Teacher Wei all the reaction steps at that time, and there will still be problems?" the school girl asked curiously.

"Teacher Wei and I don't have an orthodox background in organic synthesis. We are crossing the river by feeling the stones. Moreover, for things like synthetic experiments, it is often one thing to envision, and another to make it. Cooperate with various analytical instruments to reverse the deduction."

"Then what should we do, senior sister has been busy for two days just like us."

"That depends on how much material she put in at the beginning, and whether there is any stock of the product of the previous reaction. For example, we synthesized 5 grams of the product at one time, and this time the bromine substitution used 500 mg. There are many opportunities to try."

"Hmm... I hope it's in stock."

...

More than an hour later, the two completed the separation and purification of the last PDI product.

This time the yield was slightly lower, and only 4.2 grams of the product was obtained, but judging from the results of spotting, the purity is not bad.

Xu Qiu copied it to the simulation laboratory, and arranged for simulation experimenters to do basic characterization and device optimization.

Subsequently, Han Jiaying took 500 mg of the product and added a liquid bromine substitution reaction.

With Xu Qiu looking after her, there was no problem.