Dissymmetry enhancement in enantioselective synthesis of helical polydiacetylene by application of superchiral light
Authors: Sizhen Shan
Yan Kuai
Gang Zou
Jingang Hu
Lin Yang
Chenlu He
Douguo Zhang
Qijin Zhang
Guang Yang
Journal: Nature Communications (2018)
Discipline: Multidisciplinary
Keywords: Superchiral light; circularly polarized light; chiral molecules; optical dissymmetry; asymmetric photochemical reactions
Affiliations: CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, iChEM, University of Science and Technology of China, 230026, Hefei, Anhui, China., College of Science, Northeast Forestry University, 150040, Harbin, China., Department of Optics and Optical Engineering, Institute of Photonics, University of Science and Technology of China, Number 96 Jinzhai Road, 230026, Hefei, Anhui, China., Department of Optics and Optical Engineering, Institute of Photonics, University of Science and Technology of China, Number 96 Jinzhai Road, 230026, Hefei, Anhui, China. ., CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, iChEM, University of Science and Technology of China, 230026, Hefei, Anhui, China. .

Abstract:  Superchiral light, generated by the interference of two counter-propagating circularly polarized light (CPL) with same frequency, opposite handedness and different intensity, exhibits enhanced dissymmetry in its interaction with chiral molecules, and has the potential for ultrasensitive detection and characterization of chiral molecules. It is anticipated that the enhanced optical dissymmetry in superchiral light (SCL) field may be utilized to promote asymmetric photochemical reactions efficiency. Herein we reported SCL impart greater chiral bias to trigger asymmetric photo-polymerization reaction from initially achiral diacetylene (DA) monomer, and the enhanced optical dissymmetry for whole polydiacetylene (PDA) films could be achieved. An explanation based on the chiral transfer and amplification of chiral bias from SCL during the polymerization process has been proposed. Moreover, thus formed chiral PDA films polymerized by SCL exhibited enhanced enantioselective recognition ability, and can serve as a direct visual probe for the discrimination of some specific enantiomers. 

Retracted: No

PubPeer comments:
 The microscopic images presented in this article correspond to a sample previously reported by the same authors (J. Mater. Chem. C, 2017,5, 5135) which do not correspond to the one described herein. Indeed, figures 2b and 2d match with the figures S12a and S12b of the supporting information of the [J. Mat. Chem. C](http: www.rsc.org suppdata c7 tc c7tc01039g c7tc01039g1.pdf). ![file] It worths mentioning that changes in resolution and exposure point to different micrographs but a careful examination clearly evidences the common origin of the pictures. Fig. S12a and S12b [were already shown] to originate from the same sample while presented as two different one. Thus, a similar false claim has been done a second time by the author in this article. , 
 Response: Thanks for serious comment. These comments are appreciated. Thank you very much for reminding us the mistake. This work was finished in 2018 and the purpose of the two TEM figures were to present the morphology of the PDA after irradiation with CPL and SCL. We checked our original TEM figures immediately after your reminder and found that we have made a mistake when selecting the pictures among many very similar TEM figures. We apologized for our negligence in preparing TEM figures. The corrected figures for Fig. 2b and Fig. 2d are shown below but have no bearing on the conclusions in this study. We are very sorry for causing the inconvenience and misunderstanding. We will contact the editor immediately for this corrections. We thank you again for this helpful comments. ![file] , 
 As any spectroscopist already observed, on a wavelength scale, absorption or emission spectra tend to become larger upon red shifting. These is due to the fact that wavelength is inversely proportional to energy. That is why for a same compound, when shifts are depicted on absorption spectrum or CD spectrum (difference of left- and right-absorptions) without such enlargement, something seems wrong. Thatu2019s clearly my concern about Supplementary figure 6. ![file] Then, one could ask how such figure could have been edited to create such shift. The simplest way would be to take to similar spectrum, recorded on the same compound, and manually shift one of those two on a picture editor. ![file] The only slight issue is that, if both spectra were record on the same range, a part of the curve is missing for the u201cshifted spectrumu201d and has to be complete with a created line (either drawn or taken from another spectrum). This kind of manipulation can be sometimes evidence by the presence of an undesired break where both lines connected. Another constraint induced by this process will be the need to repeat it as many time you are supposed to have samples. Otherwise, you can also copy paste the same spectrum on an overlay with different colours slightly changing respective height. Unfortunately, both the u201cundesired breaku201d and background noise will be identical as well for all spectra, like it is observed on the supplementary Fig. 4. ![file] All these evidences clearly point to a manipulation of data presented in this manuscript. It is worth noticing that the exact same editing was already shown in another article by the same authors ([link PubPeer] ). , 
 It appears that the second spectrum used in the previously presented simulation of edition of the Supplementary Fig. 4 was way more similar to the first one. Actually, addition of a slight rotation to the translation of the red spectrum allows a pretty good overlay with the blue curve. The following figure depicts the corresponding transformation. Thus, both spectra probably originate from two different measurements performed on the same sample. ![file] , 
 #3 Response: Thanks for serious comment. These comments are appreciated. As shown in Fig. S6, PDA films exhibited blue-to-red phase shift is the basic property of the material. The UV-Vis spectras in Fig. S6 of blue and red phase PDA were obviously different at 600-800 nm, as well as the background signals of the two curves at 300-800 nm. When one of the curve is shifted to another curve (as you manually shift of the picture), it is obvious that the two curves cannot be overlapped. This difference can be judged by the naked eye. Meanwhile, we did the same experiment immediately after your comment, the UV-Vis spectras of the same sample before (blue phase) and after (red phase) heat treatment were shown blown, similar results could be easily obtained. ![file] As for the comment on Fig. S4, which exhibited blue phase PDA obtained by irradiated with SCL and CPL at the same light intensity and time. As shown in Fig. S4, the curves were slightly not overlapped with each other at some wavelengths. As we all known, the UV-Vis spectraS of PDA are very similar, especially the samples came from LB technique, usually causing the misunderstanding by many readers. Meanwhile, the change of light source inside of the Shimadzu UV-2550 PC spectrophotometer happened around 400 nm, which leads to the u201cundesired breaku201d. In addition, we did the same experiment immediately after your comment, the UV-Vis spectra of the blue phase PDA was shown blow, similar u201cundesired breaku201d was happened. ![file] , 
 #4 Response: Thanks for serious comment. However, we donu2019t agree with the manually rotation on the picture, which could lead to misunderstanding. We could obviously distinguish the difference between the two curves, not only the absorption curve at the end of the wavelength, but also the background signals. In order to clarify the blue-to-red phase transition of PDA films upon heating treatment more clearly, we repeated the experiment after your serious comment immediately. Firstly, we prepared a PDA sample in blue phase, and it exhibited typical intense absorption maximum at about 645 and 594 nm, which is similar to the picture you mentioned. Secondly, the sample was put in the oven at 70 u00b0C for 8 min, which was a little shorter than that in the paper online (10 min). Thus, we could also observe little blue phase PDA, even though the whole film was mostly in red phase (as shown in photograph). The incomplete red phase PDA exhibited typical absorption owing to the classical thermochromic phase transition of PDA backbone. Importantly, the incomplete red phase PDA exhibited a weak absorption peak at around 638 nm, which was ascribe to the little blue phase PDA. Although it was an incomplete red phase PDA, the curves of blue and incomplete red phase PDA were very similar. If the incomplete red phase PDA sample was put in the oven for another 2 min, we could get complete red phase PDA. We could observe that the curves of blue and red phase PDA were almost the same, except for the position of the absorption peak, which is the typically characteristic of BSDA monomer used in experiment. If the experimental conditions were better controlled, the curves would be more similar. We thank you again for your comment, and hope above explanation will satisfy you. ![file] , 
 I appreciate the quick double answer. Indeed, these new pairs of curves look way more different than those presented in the article. **Now**, the bandwidth changes in accordance to the change of wavelength range. Thus, I have nothing to comment about these new figures. However, **you did not explain the identical background noise on figure S4.** I had already mentioned the slight difference of height in between the different curves. Looking to Shimadzu documentation, I see that the  Lamp interchange wavelength can be set between 282 nm and 393 nm which do not correspond to your explanation ( undesired break at 410 nm). Furthermore in your last experiments, these breaks seem to appear at different positions on your spectra (contrary, to the perfect match observed on Fig. S4). Producing, new data do not help do understand what was going on with the previous ones; particularly when the new data do not present the same features than the original ones (changing bandwidths). My different observations rely on features that can be easily corrected once known. For example, running five times the same experiment on the spectrophotometer will generate five different spectra (with different background noise). So, a more convincing overlay could be obtained after an editing process but it will not clear the issue that was identify in the first place. , 
 #7 Response: Thanks for serious comment. Five curves in Fig. S4 were mainly overlapped, expect for the slight difference at the absorption peak position. Although the curves were slightly different, they do look very similar, especially the background noise, which also makes us very confused. We repeated the experiment after your response immediately, the UV-Vis spectra of three different PDA samples was shown blow. As shown in the UV-Vis spectra, three different curves were mainly overlapped, and the background noise of different curves seemed similar to each other. Besides, the  undesired break appeared in different three curves at around 410 nm, which is very similar to the article online. We have contacted the instrument engineer in the hope of solving this problem. We will pay attention to this problem and avoid misunderstanding of readers. We thank you again for your comment. ![file] , 
 #8 I thank the author for this new update. Indeed, a malfunction could explain the break at 410 nm but not the identical background noise, observed on the whole range of the spectra, on Fig. S4. ![file] , 
 #9 Response: Thanks for serious comment. In order to eliminate your doubts, we provided the raw data diagram from 200-800 nm, as shown below. We could find obvious differences in the diagram. ![file] As for the background noise, we reduced the thickness of the curves, which would cover up a lot of information about the background noise. Then, we zoomed in the curves on the raw data diagram to see if the background noise was the same. Just zooming in on the picture in article, we cannot get the key information. As shown below, five curves exhibited different background noises, indicating that five curves came from different samples. I hope it helps, and there is no need for more discussion. , 
 #9 As for the background noise, we reduced the thickness of the curves, which would cover up a lot of information about the background noise. Then, we zoomed in the curves on the raw data diagram to see if the background noise was the same. Just zooming in on the picture in article, we cannot get the key information. As shown below, five curves exhibited different background noises, indicating that five curves came from different samples. I hope it helps, and there is no need for more discussion. ![file] , 
 #10 Thanks for serious answer. Despite a high-resolution, the image you provided does not allow any clear comparison due to the large curve thickness. Nevertheless, zooming in the area that I previously discussed (#9), the background noises seem now pretty different. I do not understand such difference. Are you sure that it s the same data? ![file] Could you provide the same zoom you did for comment #11, with a lower thickness, for the range 380-600 nm? Thank you in advance for these clarifications. , 
 #12 Response: Thanks for your comment. It is not appropriate to draw any conclusions by simply zoom in the picture in article. On the raw data diagram with the large curve thickness, three curves in red, blue, and purple color (the curves in the middle) were highly overlapped, causing the background noise to be covered up. However, we could observe that the background noise near 300 nm of the diagram in article was obviously different. ![file] Meanwhile, we provided the same zoom with a lower thickness on the raw data diagram, for the range 400-550 nm. The background noise of the five curves were slightly different. In addition, we have asked the engineer to update the instrument, which could avoid the same misleading for readers in the future. I hopes it helps. ![file] , 
 #13 Thanks a lot for this new high resolution overlay of the area I discussed in comment #9. I agree that  It is not appropriate to draw any conclusions by simply zoom in the picture in article and I think it is why it is so important to allow an answer from the author for each comment of the reader. Unfortunately in absence of raw data (tables of coordinates), looking closely to details in the figures of an article is the only way to check the corresponding experiments. I really hope that editors will ask for this kind of data in the future to make any manipulation more difficult. I had a doubt about the fact the data you provided in comment #10 were the same presented in the article. Overlaying the high resolution zoom in this data (#13) with the exact same area of the figure S4 confirms the presence of differences that were not on the Fig. S4. In particular, the blue curve seems less noisy and does not match with the identical noise that was observed on Fig. S4 (while the green curve matches perfectly). ![file] I am pretty convince that the second figure of comment #13 does not correspond to the data that were used to produce Fig. S4. I think a smoothing may have been apply. Although different, the four curves present similarities that can not be due to the expected random noise. It appears looking closely on the area framed in red in the following figure that the green curve is shifted by 1 nm to the higher wavelength and that different smoothing factors could have been applied to generate the 4 other curves. For example, the symmetry in the series of coordinates in the red rectangle is clearly conserved for the 5 curves (a possible effect of the smoothing). ![file] , 
 #14 In addition to my previous comment, we can also observed that the precision of the absorption measurement changes between the different curves. It is impossible because it is an internal characteristic of the apparatus. Drawing horizontal lines connecting coordinates of the green curve forms a regular pattern and gives a good estimation of the precision of the measurement. For the 4 other curves, the same process can t be done. This is another clue pointing to a smoothing process. ![file] I do not understand why the red lines do not match to the vertical scale as it should be. Finally, the absorbance is never expressed as an arbitrary unit. , 
 #14 #15 If you insist on zooming in the picture for comparison and insist on your point, I can not help more. , 
 #16 Actually, **you could provide a high-resolution zoom in the raw data corresponding to the comment #9**. I think I clearly demonstrate the differences with the previous data you presented. I am really sorry if I have to insist. As I wrote, zooming in low resolution data is the only thing I can do right now. **I have a legitimate concern about Fig. S4** (see #9) and you are the only one that seems ready to help me. I thank you for all your helpful answers. , 
 In Fig. 8, the data interval is not constant contrary to what would be expected. Furthermore, these intervals change from Fig.8a to Fig.8b. ![file] , 
 #18 Thanks for your comment. Actually, the ideal experimental results of the data interval should be constant. However, the angle of the polarizer can only be adjusted by the experimenter in our instruments, resulting in the data interval was not constant with some randomness. We tried our best to ensure that these data were taken at equal intervals and control the angles in Fig.8a and Fig.8b to be consistent. Above operation did not affect the curve fitting. There are many similar diagrams about SHG-LD experiment with unequal data intervals appeared in the previous literature, you can check them yourself. Hope it helps. , 
 #19  ...the angle of the polarizer can only be adjusted by the experimenter in our instruments, resulting in the data interval was not constant with some randomness . I am concern about such a good overlay between many points (green crosses) of Fig8a and Fig8b considering the inherent randomness of your measurement. Furthermore, the fitting seems pretty odd as it doesn t intercept all the points. Also, I notice that a slight vertical stretching or compression is able to perfectly overlay the different bands observed on these figures. What s the chance that completely random data sets behave like that. ![file] ,