Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism

Round 1

Reviewer 1 Report

The manuscript  "Fluorescent Azobenzene-Containing Compounds: from Structure to Mechanism" written by Lulu Xue et al. represents a literature survey related to low-molecular azobenzenes, multi-azobenzenes, and azobenzene-containing polymers which possess fluorescent properties. This review tries not only to list the examples of the azobenzenes with afore-mentioned properties but to describe the manipulations to the chemical structure of azos which would promote the targeting properties. It was done in the original papers following the rules of material science and its rational design approach, and the present manuscript summarizes the examples of the original results.

This paper is probably publishable, but to my opinion, its text should be revised before the final decision is made by the editor of the Journal.

First of all, it is unclear, which relation the authors have to the described problem. Usually, the authors provide the review of something which they are familiar to and the particular paragraph of the paper begins in this case with the following words: "As we have shown in our previous publications..." In this case the reader understands the authors contribution to the problem.

Another concern is related to terminology: line 31 - "intramolecular rotation of single bond" - what do the authors mean here? how the bond itself can rotate?  line 45 "methods" - another term should be used here, since method is usually reffered as experimental techniuque but not as some manipulation to the chemical structure or to the system composition. Line 158 "bad" solvent, please replace by poor solvent. line 176 "fluorescence .... IS more complicated..." line 188: macromolecule and polymer are synonyms, and what the authors meant by "macromolecules" is usually called multiazobenzene-containing, but low-molecular compounds, like the star-shaped molecule illustrated in Figure 10. Please correct. 

It is also recommended to include a paragraph summarizing theoretical studies related to the targeted properties, and probably here the authors will find more information about the mechanisms underlying the fluorescence that the effects coming from various manupulations to the structure or composition.

What is also strongly recommended is not just list some examples from the literature, but write the review more critically. Conclusion also should be re-written and the ideas should ne described more precisely, how to controle, enchance or supress the fluorescent properties.

The part 5 provides the examples of so-called coordination complexes/compounds. In this regard it would be interesting to get from the authors the conclusion why the coordination helps the fluorescence.

 

Author Response

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Reviewer 2 Report

The present paper shows an overview of the recent progress in the chemistry of fluorescent azobenzenes. This class of organic molecules are of a great importance, from both, theoretical and experimental point of views. This review paper is well-written and covers the recent progress in the filed in a constant way. I have to admit, that I am far more familiar with theoretical work on the studied systems, so I will restrict my comments to this part of the paper. In my opinion this is very interesting paper, and I would recommend acceptance of the manuscript, after dealing with some minor points.

* In the part where the substitution effect are discussed the authors can quote some Angelini’s papers (for instance: https://doi.org/10.1016/j.molliq.2019.04.048 or https://doi.org/10.1021/acs.joc.5b00898).

 

* The authors can also consider to quote some of the recent paper on the photoisomerization azobenzene derivatives: https://doi.org/10.1002/chem.201703376 and DOI: 10.1039/D1SC01717A

Author Response

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Reviewer 3 Report

This manuscript is a review paper regarding fluorescent azobenzene and its possible mechanism of fluorescence emission. This manuscript has significant issues to be considered as a review paper, as follows:

 

1. The total number of references are 52. Although there is not an absolute number for required references, typical review papers should have more than 100 references. Just one of many examples that requires more references is in Line 56 & 57:

“… which has been utilized for making smart switches [8], self-assembly materials [9], light-responsive liquid crystals [4, 10, 11], gels [12] etc.”

 

Each of listed applications has only one or a few references. This limited number of references won’t be able to address all previously reported seminal works.

 

2. The authors claimed that “we described the recently reported progress.” However, there are not many recent papers cited: two papers published in 2020 and one paper published in 2019 in the references. Addressing a greater number of recently reported paper should be very important particularly for this review paper that has rather shorter length than other more comprehensive review papers.

 

3. The length and the scope discussed in this manuscript is rather short to be considered as a comprehensive review paper. However, explanation on each sub-topic and each cited reference is not sufficient to be considered as a short yet focused review paper. One of many examples is from Line 181:

“…extensive studies on the aggregation luminescence of azobenzenes have been performed. Chen et al. designed a series of azopyridine-containing three-arm star salts 12 (see Figure 10) [32], which present fluorescence enhancement owing to the restriction of intramolecular motion upon addition of a poor solvent (H2O).”

 

One sentence from one reference should not be sufficient to convince “extensive studies on the aggregation luminescence of azobenzenes.”

 

As above, this manuscript has rather limited scope with shorter length compared to other previous more comprehensive review papers, for example,

https://doi.org/10.1016/j.ccr.2017.05.009

https://doi.org/10.1016/j.progpolymsci.2003.07.002

https://doi.org/10.1016/j.aca.2015.10.022

 

If that is the case, this paper must have a clear point of difference from previous review papers. It can be, for example, addressing the recent papers or focusing on a certain sub-topic. Based on the three reasons above, unfortunately, this manuscript cannot convince these points.

Author Response

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Round 2

Reviewer 1 Report

I do not have further comments or recommendations regarding the scientific content of the paper. Only a minor spell check is required.

Author Response

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Reviewer 3 Report

Thanks for addressing the reviewer’s previous comments. New comments for the revised manuscript are as follows. Some comments could be minor, but the numbers of these comments are not small, so the major revision is requested.

 

More references may need to be included in each mechanism. For example, is there only one reference (reference 50) that introduced various derivatives onto azobenzene to see steric hinderance? Although the authors select one representative reference and focus to explain that, all relevant references that studied the same methods need to be added.

 

Figures need to have appropriate copyright permission.

 

Line 37, 181, and 198: A sentence starting with 'while' has to be paired with the main sentence which is not starting with 'when' or 'which'. For example, line 218 is correct. 

 

Line 78: If a reference has multiple co-authors, it should be called “Han et al.” The same error is repeated in other parts. All errors need to be fixed.

 

Line 155: "Tang's team" is not consistent with other references. It should be “Tang et al.”

 

Line 119 to 125: There is no comparison to a compound without the guest part. How can we tell if the compound with the guest enhances emission of fluorescence?

 

Line 130: The reference 57 has two authors. In this case, it needs to put both names instead of using ‘et al.’ or using only one name.

 

Line 130 to 137: Additional description may be required. What is T0 to T90 in Figure 6? How can continuous irradiation data explain the guest impact? Or is the continuous irradiation another mechanism to control PET?

 

Line 141 to 149: It needs to check the grammar. It is recommended to separate a long sentence to multiple shorter sentences. Brief description consisting of three long sentences would be very difficult for readers to understand the mechanism. Additional figure would also be helpful.

 

Line 196: There is no 12a mentioned.

 

Part 4 and 5: All figures (Figure 8 to 19) present chemical structures. Additional figures to present supporting data would be helpful for readers to understand these mechanisms. A few examples could be images of micelle/vesicles, UV-Vis spectra as a function of aggregation, UV or pH responses, etc.

Author Response

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Round 3

Reviewer 3 Report

Thanks for accepting the reviewer's comments.  I have only a few minor comments:

If abbreviations from the original paper are used, those need to be explained. For example, in Figure 11 caption, what is fw? What is 10TBMB? In Figure 17 caption, what is ETO? 

Except these above, I agree with publishing this manuscript. Thank you.

Author Response

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