Control of the Organization of 4,4′-bis(carbazole)-1,1′-biphenyl (CBP) Molecular Materials through Siloxane Functionalization

Round 1

Reviewer 1 Report

The manuscript presents the functionalization of 4,4′-bis(carbazole)-1,1′-biphenyl (CBP) with siloxane units of various length. It leads to significant destabilization of the crystal phase, which enables obtaining the less-ordered states in lower temperatures. The phase identifications is made based on the results of polarizing optical microscopy and X-ray diffraction. The photophysical properties in solutions and of thin films are investigated. I recommend the publication of this work after minor revision. My remarks are given below:

lines 58, 65, 66, 67, 73, 464 – there are some spaces and hyphens “ -” in the text which probably should be absent

line 176 – Fig. 4d shows the supercooled liquid phase, not mesophase, according to the main text (line 222)

Author Response

We are thankful to the reviewer for pointing out miswritten characters and errors in the text.

 

1) lines 58, 65, 66, 67, 73, 464 – there are some spaces and hyphens “ -” in the text which probably should be absent

We went through the whole manuscript to correct all typo errors, including the one mentioned.

 

2) line 176 – Fig. 4d shows the supercooled liquid phase, not mesophase, according to the main text (line 222)

The reviewer is perfectly right, and we are thankful for noticing a mistake in the figure caption of Fig. 4. It was therefore corrected as mentioned below:

Old caption of figure 4 in lines 174-176: "SWAXS patterns of the CBP materials recorded at room temperature: a) CBP-2Si₃ (solid state), b) CBP-4Si₃ (liquid phase), c) CBP-2Si₁₀ (pristine, solid state) and d) CBP-2Si₁₀ (after melting, in the mesophase)."

New caption of figure 4: "SWAXS patterns of the CBP materials: a) CBP-2Si₃ (solid state at 20°C), b) CBP-4Si₃ (liquid phase at 20°C), c) CBP-2Si₁₀ (mesophase at 10°C) and d) CBP-2Si₁₀ (supercooled liquid phase at 20°C)."

Reviewer 2 Report

This article is about Control of the organization of 4,4′-bis(carbazole)-1,1′-biphenyl 2 (CBP) molecular materials through siloxane functionalization. It is very well written with recent important references. However, prior to publish some minor revision should be taken into account. 

1. Explain the reason for dual peak in the emission curve.

2. How the authors have calculated the quantum yield? And how it relates with intensity photoluminescence peak?

3 Have authors also calculated the full width and half maxima (FWHM)? If yes, kindly mention.

4. Kindly add some more recent references related to your work in the introduction section.

Author Response

We are thankful to the reviewer for his careful reading and for his valuable suggestions. We answered all the points he/she addressed as detailed in the joint document.

Author Response File: Author Response.pdf

Reviewer 3 Report

Reviewer’s comment

This original article describes the self-assembling behaviors of four CBP compounds bearing oligosiloxane

unit at the extremity of sidechain. In this study. the authors investigated their phase transition behaviors by

polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction measurements.

Furthermore, photophysical properties of oligosiloxane-modified CBPs were experimentally and theoretically

revealed by UV-vis and photoluminescent spectroscopies as well as DFT calculation. The concept described in

this article will be helpful to understand the self-organization of oligosiloxane-modified aromatic compounds as

well as the precisely control of nanostructure based on “nano-segregation”. Although, the present manuscript has

some issues as described later, I think that the overall is good. Therefore, I recommend that the manuscript should

be acceptable after minor revision on the findings that I point out as following.

Comments on the manuscript:

1. (p.3, Figure 1)

The chemical structure of CBP-2Si10 in Figure 1 should be changed. I think that the description of “n~8” is

unsuitable. The subscript in the chemical structure must be “n”. The description of “n ≈ 8” should be placed in

the side of “CBP-2Si10”.

2. (p.3, Synthesis; Characterization of CBP-2Si10 in ESI)

Because the oligomer uniformity affects to the physical properties, the polydispersity index of CBP-2Si10

should be estimated by size exclusion chromatography (SEC). Please show the value of polydispersity index

and provide SEC trace. In addition, please mention the assignment of following signals on 1H- and 13C-NMR

spectra of CBP-2Si10. The corresponding signal are appeared at  = 1.3, 3.5 ppm and C = 30 ppm. Please

justify the chemical purity.

3. (p.5, Figure 2)

Why is the indicated temperature range of the DSC curves not same? Please explain.

Are the DSC curves shown in Figure 2 for the first cooling and second heating scans? If so, the authors should

state in plot or caption.

4. (p.5, POM study; p.8, lines 231-232)

Please display the POM images in the crystal (soft-crystal) phase of CBP-2Si3 at room temperature. In p.8,

why did the authors use the “soft crystal phase” not “crystal phase” for the solid state of CBP-2Si3 at room

temperature. Please briefly mention in the manuscript.

5. (p.6, Figure 4)

Although the shoulder found at q = 0.16 Å-1 in Figure 4c is possible to be considered as the diffraction of a

liquid-crystalline columnar structure such as (110) plane, is the attribution of the liquid crystalline phase of

SmE appropriate? Because fan-shaped textures can be also observed in some liquid-crystalline columnar

phases, it cannot let go of the possibility that molecules of CBP-2Si10 form a complicated columnar structure

such as B1 structure in the room temperature mesophase. Please briefly explain. If possible, I recommend to

the remeasurement of XRD for the pristine sample of CBP-2Si10. I think the comparison between the XRD

results and theoretical molecular length for all those compounds by MM2 or DFT calculation is preferable.

6. (p.9, Figure 6; p.10, Figure 7, 8; Figure S6 in the ESI)

I firstly imagined the self-assembled structures of bent-core liquid crystals (i.e. B1, B1rev, B2 etc. [Top. Curr.

Chem. 2012, 318, 281-330; J. Am. Chem. Soc. 2000, 122, 1593.]) from Figure 6, because the molecular shapes

of CBP-2Si3 and CBP-2Si10 should be not straight bar but bended. I hope the authors discussion in this article

about the crystalline and liquid-crystalline structures of CBPs from the viewpoint of the similarity in molecular

shapes between the CBPs and bent-core molecules bearing oligosiloxane units [J. Am. Chem. Soc. 2004, 126,

14312; J. Am. Chem. Soc. 2006, 128, 3051; Chem. Mater. 2015, 27, 4525; CrystEngComm 2020, 22, 8412.].

For Figures 6, and 7, I request the replacement of illustrations to the other one, which is more visually

imaginable of the molecular orientation of CBPs in the crystal or liquid-crystal structures. I think the present

illustrations are unsuitable, because the oligosiloxane units are linked by covalent bond via aliphatic spacer to

central CBP core. In addition, I do not deny the existence of dynamic short-range molecular order in a liquid

phase. However, I think the illustration of the “liquid” in Figure 7 and Figure S6 is inapt as following reasons.

The intermolecular distance in isotropic liquid phase should be longer than that in mesophases. In addition,

the macroscopic layer structure and molecular order must be broken in the liquid phase so that optically

isotropic. Thus, the illustration should be fixed as considering the above issues. Since these two figures are

overlapped, the authors should delete either one. If the authors can use Chem3D or similar modelling software,

the three-dimensional molecular models should be constructed by using the software. The three-dimensional

molecular models must be useful for schematically depicting of molecular packing in several phases. Although

I guess that Figure 8 could be deleted depending on the situation, the change of illustrations in Figure 8 should

be also required.

7. (p.12-15, photophysical property)

Please discuss the difference in the optical band gaps and emission maxima between theoretical values and

experimentally obtained values.

8. (p.15, TOF mobility)

I think that the measurement conditions of the TOF measurement such as excitation light source, sample

thickness and applied voltage so important. Please described the conditions. If the authors want to measure the

TOF mobility in crystalline phase, the thick sample is favorable. However, the thick sample often provides the

dispersive photocurrent decay. In order to obtain the large domains with poor trapping sites, the cooling rate

must be precisely controlled. In addition, the additional purification can be helpful, because the ionic impurities

inhibit efficient carrier transport. If the authors are possible to carry out it, I recommend the remeasurement

according to the above cautions. If CBP-2Si₁₀ forms B1-like structure at room temperature, I guess that the

electron carrier transport should be hindered so that low TOF photocurrent. In contrast, CBP-2Si10 forms good

SmE structure, high TOF photocurrent should be found. Therefore, I am interested in their carrier transport

properties.

9. (In the whole of the manuscript and ESI)

Please check the font of physical quantity. The representative alphabet of physical quantity must be italic

font. Furthermore, please check the garbled characters written in symbol font. The unit notation rule should be

unified. The unit of “cm²/V.s” must be changed to “cm² V⁻¹ s⁻¹”. In case of SI derived unit, the half-space

should be inserted not “.” between each SI units.

Summary:

The concept described in this article will attracts broad research interests for material scientists as well as the

expert of liquid crystals. The authors have been evaluated four-types of CBPs and got good results, the discussion

described in present manuscript seems to be reasonable except for the issues that I point out above. I recommend

that the manuscript acceptable after minor revision.

Comments for author File: Comments.pdf

Author Response

We are grateful to the reviewer for his careful reading and his valuable comments. All comments have been succesfully addressed, as detailed in the document here enclosed.

Author Response File: Author Response.pdf

Reviewer 4 Report

This manuscript can no doubt be published in ‘Molecules’ with little or no editing.

List of minor сorrections is contained in the attached pdf file

 

Comments for author File: Comments.pdf

Author Response

We are grateful to the reviewer for his careful reading and his valuable comments. All comments have been succesfully addressed as detailed in our response here enclosed.

Author Response File: Author Response.pdf