Angle-Resolved Photoemission Study on the Band Structure of Organic Single Crystals

Round 1

Reviewer 1 Report

The manuscript presents a well organized and accessible review. Minor problems with language are detected. I support publication in present form

Author Response

We’d like to thank the reviewer for the careful review and kind approval.

Reviewer 2 Report

The work entitled "Angle-Resolved Photoemission Study on the Band Structure of Organic Single Crystals" by Ke Wang, Ben Ecker and Yongli Gao is devoted to shred some light to the ARPES technique for studying electronic band structure of different materials, including conductors, semiconductors and perovskites, which contain organic molecules. The work is written in clear English, has well-formulated goal and sufficient data to perform a good review.

Despite this work makes a good overall impression, minor revision is required to make it even more valuable for readers. Some comments are provided below:

1. Fig.1 can definitely be improved. A lot of free space is seen between "a", "b" and "c" parts of the figure, while font is small. Yellow color is not proved to be used on the white (light) background, can it be changed?
2. Line 57 should be "does not show any energy loss...".
3. Lines 142 - 154 is not supported with appropriate refs. I would suggest to illustrate mechanical properties, e.g. bending crystals with several Dr. Reddy works ( C.M. Reddy, R.C. Gundakaram, S. Basavoju, M.T. Kirchner, K.A. Padmanabhan, G.R. Desiraju, Structural basis for bending of organic crystals, Chem. Commun. 1 (2005) 3945. https://doi.org/10.1039/b505103g. and P.P. Bag, M. Chen, C.C. Sun, C.M. Reddy, Direct correlation among crystal structure, mechanical behaviour and tabletability in a trimorphic molecular compound, CrystEngComm. 14 (2012) 3865. https://doi.org/10.1039/c2ce25100k. ) at least, as well as first example of bending crystal at liquid nitrogen temperature by Rychkov et al. (S.G. Arkhipov, E.A. Losev, T.T. Nguyen, D.A. Rychkov, E. V. Boldyreva, A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures, Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater. 75 (2019) 143–151. https://doi.org/10.1107/S2052520619000441. and T.T. Nguyen, S.G. Arkhipov, D.A. Rychkov, Simple crystallographic model for anomalous plasticity of L-Leucinium hydrogen maleate crystals, Mater. Today Proc. 25 (2020) 412–415. https://doi.org/10.1016/j.matpr.2019.12.137.). A comprehensive review of mechanical properties can be found at work P. Naumov, S. Chizhik, M.K. Panda, N.K. Nath, E. Boldyreva, Mechanically Responsive Molecular Crystals, Chem. Rev. 115 (2015) 12440–12490. https://doi.org/10.1021/acs.chemrev.5b00398. Solubility and different polymorphs are well illustrated at works J. Bernstein, Polymorphism in Molecular Crystals, Oxford University Press, New York, 2002., Y. Zhang, Z. Yang, S. Zhang, X. Zhou, Synthesis, Crystal Structure, and Solubility Analysis of a Famotidine Cocrystal, Crystals. 9 (2019) 360. https://doi.org/10.3390/cryst9070360., L. Nicoud, F. Licordari, A.S. Myerson, Estimation of the Solubility of Metastable Polymorphs: A Critical Review, Cryst. Growth Des. 18 (2018) 7228–7237. https://doi.org/10.1021/acs.cgd.8b01200., etc.
4. Line 275 "demonstrated the similar behavior" instead of "behaviors"
5. At section 3 "Organic Semiconductors" many examples are illustrated with computational works. It is recommended to highlight in the introduction, that computational methods are used in many different fields (e.g. A.H. Mazurek, Ł. Szeleszczuk, D.M. Pisklak, Periodic DFT calculations—Review of applications in the pharmaceutical sciences, Pharmaceutics. 12 (2020). https://doi.org/10.3390/pharmaceutics12050415.,  D.A. Rychkov, A Short Review of Current Computational Concepts for High-Pressure Phase Transition Studies in Molecular Crystals, Crystals. 10 (2020) 81. https://doi.org/10.3390/cryst10020081., ) as well as more specific (e .g. N. Van Trang, T.N. Dung, N.T. Cuong, L.T.H. Hai, D. Escudero, M.T. Nguyen, H.M.T. Nguyen, Theoretical study of a class of organic D‐π‐A dyes for polymer solar cells: Influence of various π‐ spacers, Crystals. 10 (2020). https://doi.org/10.3390/cryst10030163.) I am sure that  several additional papers can be found to illutrate this, including journals from MDPI.
6.  Some references are given in capital letters (please see 21, 50, 52, 69 etc.), which looks being not according to the rules of the journal.

Finally I should conclude that despite some minor changes are needed, the paper looks solid and may attract general chemical audience. It would be useful for many young researchers, studying new organic materials.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors wrote a review on angle-resolved photoemission spectroscopy (ARPES) focusing on studies of the electronic band structure of organic single crystals, including organic charge transfer conductors; organic semiconductors; and organo-metallic perovskites.  ARPES technique is very important for investigating the electronic band structure of crystalline solids and is crucial for the development of functional materials, especially in optoelectronic devices.

The article is very well written and provides a comprehensive review about ARPES which can be very helpful to those researchers working on organic and hybrid metal organic conductors and semiconductors with applications in optoelectronic devices.  The references are appropriate for this type of article.  The paper has some minor revisions which need to be addressed prior publication.

The points to be corrected are the following:

i) In section 4. Organo-metallic perovskite charge transfer crystals, the authors start the section explaining that perovskites have a cubic structure. While this is true for the prototypical CaTiO₃, which is the structure from which all the other perovskites have been described having the ABX₃ general formula, the large amount of new hybrid perovskite reported are not cubic. In fact, the example given is not cubic. The authors should re-write this part of article.

ii) In the same section 4, the organic A cations methylammonium (CH₃NH₃⁺) and formamidinium (CH(NH₂)₂⁺), should be written correctly.

iii) In the article, the authors mention the reciprocal lattice.  Maybe it can be briefly mentioned that reciprocal lattice is different from crystal lattice.

Author Response

Please see the attachment.

Author Response File: Author Response.docx