Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives

Round  1

Reviewer 1 Report

The manuscript entitled "Crystal structures and optical properties of two novel 1,3,5-trisubstituted pyrazoline derivatives" prepared by Qi Feng, Wenhui Huan, Jiali Wang, Jiadan Lu, Guowang Diao and Yaqi Shan concerns two newly synthesized pyrazoline derivatives and provides structural and spectroscopic data about them, accordingly. The Authors performed proper material's analysis, namely 1H NMR, IR, then also X-ray from single crystal and powder form of both compounds. All the provided data are sufficient in order to make structural characterization of the new molecules. Then, the Authors were analyzed what is the influence of the chemical structure on the internal charge transfer (ICT) and basic spectroscopic features, namely absorption and fluorescent band for solutions in few different solvents. The latter one, fluorescence spectra, were done additionally for the solid state (single crystals).

In my opinion, several major revision in current form of the manuscript should be considered in order to be suitable for publication in the Crystals journal. All of the critical issues are pointed out below:

1) From the beginning it is not clear in the Introduction part as well as in the Conclusions part what was the goal of the paper. The Authors should improve these two parts in order to highlight more the point of planned and performed research.

 2) Introduction part is very poor and too short. The Authors did not provide sufficient data in both issues: (i) used materials (in here should be provided more literature data about the pyrazoline derivatives), and (ii) final goal of the manuscript - it is the spectroscopy part, as I suppose. So, any additional comparison with the available literature data would be well-seen. I think a lot of articles would be even convenient to make a discussion on the obtained results. Exemplary titles of papers and their doi numbers are listed below:

- High solid fluorescence of a pyrazoline derivative through hydrogen bonding, doi: 10.3390/molecules22081304

- Invelling a versatile heterocycle: pyrazoline a review, doi: 10.1039/c7ra08939b

- Low-molecular push pull pyrazoline derivatives: solvatochromic effect and theoretical insights into dye-based molecular engineering, doi: 10.1021/acs.jpca.8b04814

- Synthesis and fluorescent properties of poly(arylpyrazoline)'s for organic-electronics, doi: 10.1016/j.optmat.2016.06.042

 3) Since the main goal of the paper (as I supposed) is the proof of the ICT presence in one of the new compounds, which causes remarkable absorption as well as fluorescence shift, therefore presented and discussed results should be consistent. In my opinion:

- Fig. 7 and 8 should be combined in one (Table 5. already considers the data coming from absorption and fluorescence part)

- results presented in Fig. 9 is not consistent with the preparation part. In the chapter 2.2 Crystals' Preparation, the Authors wrote in the lines 66-67 that they growth the crystals from ethanol solvent. So, why in the further part of manuscript in the line 198-199 it was compared fluorescence shift coming from n-hexane solvent and another one from solid state (crystals), which were growth in ethanol? The comparison would be more reliable, if fluorescence shift for both compounds would be compared from the same solvent - ethanol. For the solution, directly from EtOH mixture with pyrazolines. For the single crystals - it were growth in the ethanol, as it was written before in the manuscript (lines 66-67). I suggest to add absorption and fluorescence spectra in ethanol solvent in current Fig. 7 and 8, and then compare the fluorescence shift for solid state. Then, environment for the molecules is the same. Only one changed parameter is the phase - liquid and solid. I think this is the most significant result of the paper, although for now - not reliable. Then, can be discussed more detailed and (probably) also compared with the literature. Also solvatochromic shift (as well as Stokes shift) can be discussed with the literature more significant. Nowadays, a lot of new compounds are provided to the community and the most important issue is to relate new ones to the already published/well-known.

 4) Some editor issues should be improved. As the examples, few of them were listed below:

- the text in many paragraphs is not adjusted

- maybe I missed it, but ORTEP acronym was not explained in the text (line 92)

- in Fig. 2 and 3, in the caption, proper legend due to the atom colors is useful to clarify the structures

- in the caption of Fig. 5 "the" was used two times

- Fig. 6 could be transferred to the SI file

- font number of X and Y axis, also the legend, in the current Fig. 7-9 should be increased

- English language should be improved and grammar issues polished

 5) It is not necessary, although if available, the structures could be refined using new version of the software, I mean SHELXL-2014 program.

 I encourage the Authors to improve the paper quality and make suitable to the Crystals journal.

Author Response

Dear reviewer:

Thank you for your comments concerning our manuscript entitled " Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives". We have studied comments carefully and made corrections which we hope meet with approval.

The corrections in the paper and the responds for reviewers’ comments are as follows:

Question:

1) From the beginning it is not clear in the Introduction part as well as in the Conclusions part what was the goal of the paper. The Authors should improve these two parts in order to highlight more the point of planned and performed research.

Answer for reviewer :

The introduction part has been revised as follows:

A development in the design and preparation of novel organic luminescent materials has recently been the subject of great interest from both academia and industry, including the fields of fluorescent biological labels, optical sensors and organic light-emitting diodes (OLEDs), etc [1-4]. Amongst the numerous organic luminescent materials, pyrazoline and its derivatives have received increasing attention due to their excellent electro-optical properties and wide range of applications [5-10]. In the past decades, although extensive research focused on the photophysical properties of 1,3,5-triaryl-substituted pyrazolines [11,12], 1-acetyl-pyrazoline derivatives also have attracted a lot of attention, because they have many unique advantages [13]. For example, a large number of 1-acetyl-pyrazoline derivatives show high sensitivity and selectivity toward the different metal ions and can be used as fluorescent sensors [14]. However, the relevant research about the photophysical properties of 1,3,5-triaryl-substituted pyrazoline and 1-acetyl-pyrazoline derivatives, especially in solid-state, is rare.

In this work, two novel 1,3,5-trisubstituted pyrazoline derivatives: 1-acetyl-3-(4-methoxyphenyl) -5-(6-methoxy-2-naphthyl)-pyrazoline (2a) and 1-(4-nitrophenyl)-3-(4-methoxyphenyl)-5-(6- methoxy-2-naphtyl)-pyrazoline (2b) were synthesized and their structures were confirmed by the X-ray crystallographic analyses.        The two compounds contain the same substituent groups on 3- and 5-positions, but different electron withdrawing groups on 1-position. According to the previous reports, the substituent groups on 1-position of the pyrazoline ring could primarily influence the photophysical properties [15]. Thus, the different optical-physical properties of the two compounds in solvents and solid-state were investigated and discussed. Moreover, from the view of crystallography, the introduction of the hydrogen bond acceptors, such as methoxyl and carbonyl groups, could cause the formation of hydrogen bonds, which may primarily affect their 3D crystal structures. Therefore, Hirshfeld surface analyses was also performed to give insights regarding intermolecular interactions in the two crystals.

 Question:

2) Introduction part is very poor and too short. The Authors did not provide sufficient data in both issues: (i) used materials (in here should be provided more literature data about the pyrazoline derivatives), and (ii) final goal of the manuscript - it is the spectroscopy part, as I suppose. So, any additional comparison with the available literature data would be well-seen. I think a lot of articles would be even convenient to make a discussion on the obtained results. Exemplary titles of papers and their doi numbers are listed below:

- High solid fluorescence of a pyrazoline derivative through hydrogen bonding, doi: 10.3390/molecules22081304

- Invelling a versatile heterocycle: pyrazoline a review, doi: 10.1039/c7ra08939b

- Low-molecular push pull pyrazoline derivatives: solvatochromic effect and theoretical insights into dye-based molecular engineering, doi: 10.1021/acs.jpca.8b04814

- Synthesis and fluorescent properties of poly(arylpyrazoline)'s for organic-electronics, doi: 10.1016/j.optmat.2016.06.042

Answer for reviewer :

The introduction part has been revised and the references have been added.

1.   Zhang, L.; Liu, J.; Gao, J. K.; Zhang, F.; Ding, L. High Solid Fluorescence of a Pyrazoline Derivative through Hydrogen Bonding. Molecules. 2017, 22, 1304, DOI: 10.3390/molecules22081304.

2.  Varghese, B.; Al-Busafi, S. N.; Suliman, F. O.; Al-Kindy, S. M. Z. Unveiling a versatile heterocycle: pyrazoline a review. RSC Adv. 2017, 7, 46999-47016, DOI: 10.1039/c7ra08939b.

3.  Haupa, K. A.; Szukalski, A.; Mysliwiec, J. Low-Molecular Push Pull Pyrazoline Derivatives: Solvatochromic Effect and Theoretical Insights into Dye-based Molecular Engineering. J. Chem. Phys. 2018, 122, 7808-7818, DOI: 10.1021/acs.jpca.8b04814.

4.  Vandana, T.; Ramkumar, V.; Kannan, P. Synthesis and fluorescent properties of poly(arylpyrazoline)'s for organic-electronics. Opt. Mater. 2016, 58, 514-523, DOI: 10.1016/j.optmat.2016.06.042.

 Question:

3) Since the main goal of the paper (as I supposed) is the proof of the ICT presence in one of the new compounds, which causes remarkable absorption as well as fluorescence shift, therefore presented and discussed results should be consistent. In my opinion:

- Fig. 7 and 8 should be combined in one (Table 5. already considers the data coming from absorption and fluorescence part).

- results presented in Fig. 9 is not consistent with the preparation part. In the chapter 2.2 Crystals' Preparation, the Authors wrote in the lines 66-67 that they growth the crystals from ethanol solvent. So, why in the further part of manuscript in the line 198-199 it was compared fluorescence shift coming from n-hexane solvent and another one from solid state (crystals), which were growth in ethanol? The comparison would be more reliable, if fluorescence shift for both compounds would be compared from the same solvent - ethanol. For the solution, directly from EtOH mixture with pyrazolines. For the single crystals - it were growth in the ethanol, as it was written before in the manuscript (lines 66-67). I suggest to add absorption and fluorescence spectra in ethanol solvent in current Fig. 7 and 8, and then compare the fluorescence shift for solid state. Then, environment for the molecules is the same. Only one changed parameter is the phase - liquid and solid. I think this is the most significant result of the paper, although for now - not reliable. Then, can be discussed more detailed and (probably) also compared with the literature. Also solvatochromic shift (as well as Stokes shift) can be discussed with the literature more significant. Nowadays, a lot of new compounds are provided to the community and the most important issue is to relate new ones to the already published/well-known.

Answer for reviewer :

Fig. 7 and 8 have been combined in one.

Photo-physical Properties part has been revised as follows:

The absorption spectra of the two compounds in different solvents are shown in Fig.6. Because naphthalene exhibits several maximum peaks near 350 nm, the absorption of 2a was considered an combination of 3-(4-methoxyphenyl)-1-acetyl-2-pyrazolinyl and the 6-methoxy-2-naphthyl chromophores. In addition, it could be observed that the absorption spectra of 2a exhibit a little change with increasing solvent polarity, indicating that there is no charge transfer in its ground state. Compound 2b exhibits two absorption bands around 400 nm in non-polar solvent n-hexane (Table 5), which should be ascribed to the π-π* transition of 3-(4-methoxyphenyl)-1-(4-nitrophenyl)-2-pyrazoline chromophore. Compared with other 1,3,5-triphenyl-pyrazoline and 1,3-diphenyl-pyrazolines, the absorption band shift to lower energy in the solvents of moderate polarity. The red shift may be attributed to the stronger electron-withdrawing group located in 1-position in 2b, which causes intramolecular charge-transfer (CT) character for the transition.

Corresponding to the absorption spectra , the fluorescent spectra of 2b also exhibits a large red shift in the polar solvents. When the solvent is changed from n-hexane to methanol, the red shift in their emission bands is nearly 110 nm. This characters could be found in the fluorescence spectra of some other pyrazoline derivatives, when the electron-drawing substituents exist on 1-position [21]. The red shift could be attributed to intramolecular charge transfer (ICI) state formed by intramolecular electron transfer in 3-(4-methoxyphenyl)-1-(4-nitrophenyl)-2-pyrazoline chromophore, which is effectively stabilized in polar media such as methanol and causes increase of the Stokes’ shift. In contrast, 2a exhibits only one band with fluorescence maxima centered at 358 nm in the n-hexane and no obvious change could be found with increasing the polarity of solvents. It was considered that the fluorescence of 2a arises from the 6-methoxy-2-naphthyl, and the fluorescence of pyrazoline is quenched due to the enhanced intersystem crossing from pyrazoline excited state [22].

Solid fluorescence spectra of the two crystals are shown in Fig. 7. The fluorescence spectrum of 2a is similar with that in ethanol, which exhibits two emission peaks at 360 and 374 nm. According to it crystal structure, no strong π-π interaction exists between naphthalene rings in its crystal structure, it was considered that the fluorescent emission of 2a should be attributed to monomer fluorescence of 6-methoxy-2-naphthyl chromophore. Emission peaks of 2b are centered at 556 nm. Compared to its emission in ethanol solvent, it has a red shift of 23 nm in solid state. In solid-state, the molecules are closer to each other, which result in enhancement of dipole-dipole interaction of the polarized excited-state and a larger red shift in its fluorescence spectrum.

 Question:

4) Some editor issues should be improved. As the examples, few of them were listed below:

- the text in many paragraphs is not adjusted

- maybe I missed it, but ORTEP acronym was not explained in the text (line 92)

- in Fig. 2 and 3, in the caption, proper legend due to the atom colors is useful to clarify the structures

- in the caption of Fig. 5 "the" was used two times

- Fig. 6 could be transferred to the SI file

- font number of X and Y axis, also the legend, in the current Fig. 7-9 should be increased

- English language should be improved and grammar issues polished.

Answer for reviewer :

All the issues have been revised. In addition, according to Reviewer 2, the PXRD part should be removed. Thus, we deleted Fig.6 and 6S in original manuscript.

 Question:

5) It is not necessary, although if available, the structures could be refined using new version of the software, I mean SHELXL-2014 program.

Answer for reviewer :

Unfortunately, I'm so sorry to tell you some raw data, such hkl. has been lost from computer.

Yours sincerely,

Qi Feng

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, Feng and coworkers present crystal structures of two new pyrazoline derivatives and study their photo physical properties. Overall, the research appears to be carried out thoroughly and the results were presented properly. The authors only offer one sentence of background and motivation for this work at the very beginning, leaving it unclear why the authors characterized these two pyrazolines in such detail.  This is a major weakness of this manuscript, and I suggest that some more content be added here before publishing a final draft.

Both of the pyrazolines were prepared in a similar way, first by Claisen-Schmidt and then Paal-Knor Synthesis. This chemistry is unremarkable, but adequately recorded. The authors then describe the crystal packing of these compounds, including a Hirshfield surface analysis to explain the role of hydrogen bonding in the structure. Although this is not my area of expertise, I find their reasoning here accurate and compelling. Next there is an irrelevant section (3.3) about powder X-ray diffraction analysis; apparently the PXRD pattern matches that simulated from the single crystal X-ray diffraction data. This is a fairly obvious result; if it were not true that would be more interesting than anything else in this manuscript. I suggest that this section be removed. Finally, the authors report the fluorescence properties in various solvents to provide a mechanism for fluorescence quenching. Again, this is not my area of expertise, but their reasoning sounds fine to me. 

In summary, I think that this manuscript needs a longer introduction and motivation, and that the PXRD section can be removed.

Author Response

Dear reviewer:

Thank you for your comments concerning our manuscript entitled " Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives". We have studied comments carefully and made corrections which we hope meet with approval.

The corrections in the paper and the responds for reviewers’ comments are as follows:

Question:

In this paper, the Authors describe very routine chemistry to prepare two 4,5-dihydropyrazoles and then carry out X-ray analyses of these compounds. The organic synthetic chemistry is of no novelty and this method of preparing dihydropyrazoles is very well known. The interest in this paper, then, must rest on the significance, or not, of the crystal structure determinations. I am not a crystallographer, but the work seems to have been done correctly and one can trust the results. However, whether they are of greater interest than just the structures is in doubt. I do not think that the Authors explain clearly enough the significance of the structures that they have determined - why did they do this work? What further work will these results lead to?

Answer for reviewer :

The introduction about the background and significance of this work has been revised as follows:

A development in the design and preparation of novel organic luminescent materials has recently been the subject of great interest from both academia and industry, including the fields of fluorescent biological labels, optical sensors and organic light-emitting diodes (OLEDs), etc [1-4]. Amongst the numerous organic luminescent materials, pyrazoline and its derivatives have received increasing attention due to their excellent electro-optical properties and wide range of applications [5-10]. In the past decades, although extensive research focused on the photophysical properties of 1,3,5-triaryl-substituted pyrazolines [11,12], 1-acetyl-pyrazoline derivatives also have attracted a lot of attention, because they have many unique advantages [13]. For example, a large number of 1-acetyl-pyrazoline derivatives show high sensitivity and selectivity toward the different metal ions and can be used as fluorescent sensors [14]. However, the relevant research about the photophysical properties of 1,3,5-triaryl-substituted pyrazoline and 1-acetyl-pyrazoline derivatives, especially in solid-state, is rare.

In this work, two novel 1,3,5-trisubstituted pyrazoline derivatives: 1-acetyl-3-(4-methoxyphenyl) -5-(6-methoxy-2-naphthyl)-pyrazoline (2a) and 1-(4-nitrophenyl)-3-(4-methoxyphenyl)-5-(6- methoxy-2-naphtyl)-pyrazoline (2b) were synthesized and their structures were confirmed by the X-ray crystallographic analyses.        The two compounds contain the same substituent groups on 3- and 5-positions, but different electron withdrawing groups on 1-position. According to the previous reports, the substituent groups on 1-position of the pyrazoline ring could primarily influence the photophysical properties [15]. Thus, the different optical-physical properties of the two compounds in solvents and solid-state were investigated and discussed. Moreover, from the view of crystallography, the introduction of the hydrogen bond acceptors, such as methoxyl and carbonyl groups, could cause the formation of hydrogen bonds, which may primarily affect their 3D crystal structures. Therefore, Hirshfeld surface analyses was also performed to give insights regarding intermolecular interactions in the two crystals.

Yours sincerely,

Qi Feng

Author Response File: Author Response.docx

Reviewer 3 Report

 In this paper, the Authors describe very routine chemistry to prepare two 4,5-dihydropyrazoles and then carry out X-ray analyses of these compounds. The organic synthetic chemistry is of no novelty and this method of preparing dihydropyrazoles is very well known. The interest in this paper, then, must rest on the significance, or not, of the crystal structure determinations. I am not a crystallographer, but the work seems to have been done correctly and one can trust the results. However, whether they are of greater interest than just the structures is in doubt. I do not think that the Authors explain clearly enough the significance of the structures that they have determined - why did they do this work? What further work will these results lead to? 

Author Response

Dear reviewer:

Thank you for your comments concerning our manuscript entitled " Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives". We have studied comments carefully and made corrections which we hope meet with approval.

The corrections in the paper and the responds for reviewers’ comments are as follows:

Question:

In this paper, the Authors describe very routine chemistry to prepare two 4,5-dihydropyrazoles and then carry out X-ray analyses of these compounds. The organic synthetic chemistry is of no novelty and this method of preparing dihydropyrazoles is very well known. The interest in this paper, then, must rest on the significance, or not, of the crystal structure determinations. I am not a crystallographer, but the work seems to have been done correctly and one can trust the results. However, whether they are of greater interest than just the structures is in doubt. I do not think that the Authors explain clearly enough the significance of the structures that they have determined - why did they do this work? What further work will these results lead to?

Answer for reviewer :

The introduction about the background and significance of this work has been revised as follows:

A development in the design and preparation of novel organic luminescent materials has recently been the subject of great interest from both academia and industry, including the fields of fluorescent biological labels, optical sensors and organic light-emitting diodes (OLEDs), etc [1-4]. Amongst the numerous organic luminescent materials, pyrazoline and its derivatives have received increasing attention due to their excellent electro-optical properties and wide range of applications [5-10]. In the past decades, although extensive research focused on the photophysical properties of 1,3,5-triaryl-substituted pyrazolines [11,12], 1-acetyl-pyrazoline derivatives also have attracted a lot of attention, because they have many unique advantages [13]. For example, a large number of 1-acetyl-pyrazoline derivatives show high sensitivity and selectivity toward the different metal ions and can be used as fluorescent sensors [14]. However, the relevant research about the photophysical properties of 1,3,5-triaryl-substituted pyrazoline and 1-acetyl-pyrazoline derivatives, especially in solid-state, is rare.

In this work, two novel 1,3,5-trisubstituted pyrazoline derivatives: 1-acetyl-3-(4-methoxyphenyl) -5-(6-methoxy-2-naphthyl)-pyrazoline (2a) and 1-(4-nitrophenyl)-3-(4-methoxyphenyl)-5-(6- methoxy-2-naphtyl)-pyrazoline (2b) were synthesized and their structures were confirmed by the X-ray crystallographic analyses.        The two compounds contain the same substituent groups on 3- and 5-positions, but different electron withdrawing groups on 1-position. According to the previous reports, the substituent groups on 1-position of the pyrazoline ring could primarily influence the photophysical properties [15]. Thus, the different optical-physical properties of the two compounds in solvents and solid-state were investigated and discussed. Moreover, from the view of crystallography, the introduction of the hydrogen bond acceptors, such as methoxyl and carbonyl groups, could cause the formation of hydrogen bonds, which may primarily affect their 3D crystal structures. Therefore, Hirshfeld surface analyses was also performed to give insights regarding intermolecular interactions in the two crystals.

Yours sincerely,

Qi Feng

Round  2

Reviewer 1 Report

According to my previous revision letter, here are the up-date'ed conclusions:

1) OK

2) OK

3) NOT OK - still, there is no sufficient discussion with available literature data.

4) NOT OK, still some editor issues pointed out here should be improved in the paper.

5) OK

Author Response

Dear reviewer:

Thank you for your comments concerning our manuscript entitled " Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives". We have studied comments carefully and made corrections which we hope meet with approval.

The corrections in the paper and the responds for reviewers’ comments are as follows:

Question3 there is no sufficient discussion with available literature data.

Answer for reviewer :

In order to understand the photophysical properties of 2a and 2b more deeply, we compared their fluorescence with several analogous pyrazoline derivatives: 5-(9-anthryl)-3-(4-nitrophenyl)-1-phenyl-2-pyrazoline (ANPP), 1-acetyl-3-naphthyl-5-(9-anthryl)-2-pyrazoline (APPP). The similar emission bands or characters suggests that the luminescent mechanism for these pyrazoline derivatives.

The paragraph was revised as follows:

Corresponding to the absorption spectra , the fluorescent spectra of 2b also exhibits a large red shift in the polar solvents. When the solvent is changed from n-hexane to methanol, the red shift in their emission bands is nearly 110 nm. The red shift could be attributed to intramolecular charge transfer (ICT) state formed by intramolecular electron transfer in 3-(4-methoxyphenyl)-1- (4-nitrophenyl)-2-pyrazoline chromophore, which is effectively stabilized in polar media such as methanol and causes increase of the Stokes’ shift. This characters are similar with 5-(9-anthryl)-3-(4-nitrophenyl)-1-phenyl-2-pyrazoline (ANPP), etc [21,22]. Although the electron-drawing substituent groups exist on the other positions (for ANPP, the nitro group exists on 3- position), they emit a large red shift of about 110 nm in the polar solvents, which are also caused by charge transfer from N1 to C3 in the pyrazoline moiety in the excited state. In contrast, 2a exhibits only one band with fluorescence maxima centered at 358 nm in the n-hexane and no obvious change could be found with increasing the polarity of solvents. It was considered that the fluorescence of 2a arises from the 6-methoxy-2-naphthyl, and the fluorescence of pyrazoline is quenched due to the enhanced intersystem crossing from pyrazoline excited state [23]. The similar circumstance could be found in 1-acetyl-3-naphthyl-5-(9-anthryl)-2-pyrazoline (APPP), the emission band is assigned to anthracene chromophore and is fairly insensitive to the solvent polarity [24], suggesting the same optical-physical process for these 1-acetyl-pyrazolines.

Solid fluorescence spectra of the two crystals are shown in Fig. 7. The fluorescence spectrum of 2a is similar with that in ethanol, which exhibits two emission peaks at 360 and 374 nm. According to it’s crystal structure, no strong π-π interaction exists between naphthalene rings, it was considered that the fluorescent emission of 2a should be attributed to monomer fluorescence of 6-methoxy-2-naphthyl chromophore. Emission peaks of 2b are centered at 556 nm. Compared to its emission in ethanol solvent, it has a red shift of 23 nm in solid state. In solid-state, the molecules are closer to each other, which result in enhancement of dipole-dipole interaction of the polarized excited-state and a larger red shift in its fluorescence spectrum.

Question 4  some editor issues pointed out here should be improved in the paper.

Answer for reviewer :

ORTEP means thermal ellipsoids plots, the text and acronym have been revised.

Atom colors has been added. C atoms in gray, N atoms in blue and O atoms in red

One of  two "the" in the caption of Fig.5 has been deleted.

Font number of X and Y axis and the legend in the current Fig. 7-9 have been increased.

We have check the manuscript for several times. If there is still a serious grammar or vocabulary error, please inform us.

Yours sincerely,

Qi Feng

Reviewer 3 Report

the Authors have made a good job of revising their paper and that my criticisms have been met in full. I now recommend publication of the paper as it now stands.

Author Response

Dear reviewer:

Thank you for your comments concerning our manuscript entitled " Crystal Structures and Optical Properties of Two Novel 1,3,5-Trisubstituted Pyrazoline Derivatives". 

Yours sincerely,

Qi Feng