Luminescent Diimine-Pt(IV) Complexes with Axial Phenyl Selenide Ligands

Round 1

Reviewer 1 Report

This is a study of luminescent Pt(IV) complexes by both experimental and theoretical means. It is interesting because Pt(IV) complexes have so far not received the same amount of attention as Pt(II) complexes. Although two of the three complexes investigated have been reported previously, their photophysical properties are studied here for the first time. All three complexes are seen to be luminescent, the emissive state presumably being a triplet state. However, the DFT calculations are insufficient to condifently assign the spectra. The stongest peaks of the TDDFT absorption spectra appear to be in error by more than 0.5 eV. The reason for this could be the CT character of the corresponding excited state, which might be better described by a range-separated functional (e.g. CAM-B3LYP). No attempt has been made to interpret the emission spectra by DFT calculations although this could be done with little additional computational effort by optimizing the T1 geometry. Therefore, publication of the manuscript in the present form would be premature. 

quite ok, with the occasional grammar mistake

Author Response

Dear reviewer,

thank you very much for the evaluation. 

We agree with the reviewer about the preliminary character of this study and we stress this preliminary character several time in the manuscript. Nevertheless, the situation at the moment is, that we cannot add more experiments, which we consider indeed as a problem. TR measurements would really help and we will do them in the near future.

It is also true that using other functionals for the DFT calculations might help to get a better agreement with the data. However, for DFT calculations, agreement with data is not an unequivocal sign that this functional is correct, while the other is not. Some people even say, that a good match is serendipity. I would not go so far.  I would say that our DFT results give “a good insight into the electronic structure”. Also, the results agree qualitatively well with other quantum chemical calculations on similar systems. This is why the discussion included so many other Pt(IV) complexes and even Re(I) complexes with selenolate or thiolate ligands (and might even be a bit lengthy). From the good match with these other examples (using various methods and functionals) we draw the confidence that our calculations are “ok”. DFT calculations to model emission spectra are not so simple and in first trials to do this we found no overlap – thus no emission spectra. We therefore “indirectly” assign the luminescence from the excitations as has been done by many others before.

So, we would be happy if the reviewer could accept the “preliminary” (instead of “premature”) character of our work which presents a new class of luminescent organoPt(IV) (which, in our eyes, is an important information).

Sincerely,

AK

Reviewer 2 Report

The authors report the synthesis of 3 diimine-Pt(IV) complexes with axial phenyl selenide ligands. As the authors state only the synthesis of derivative 3b is a novelty.

It is not clear the importance of the complex 3b.

Other comments:
The insets in Figure 3 are very small are not identified.
In Figure 4 all characters should have the same size.

Author Response

Dear reviewer,

thank you very much for evaluating our manuscript. Please find attached our point-by-point list of responses. All changes in the manuscript are highlighted in yellow.

Sincerely,

AXEL KLEIN

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper by Aseman and Klein et al. represents the synthesis and study of the photoluminescence of Pt complexes with theoretical insight. The complexes obtained are not novel, but the photophysical properties have not been investigated to date. Despite the absence of significant novelty, the photophysical studies could add a clue to the nature of the emission of such complexes. The paper is suitable for publication in molecules, but needs major revisions:

1. The order of text and corresponding figures/tables should be updated. For example, the figure should be inserted after its main discussion, not before.

2. The usage of neocuproine or 6,6-dimethyl-bipyridine, or ligands containing electron-withdrawing substituents seems to be more logical. All used ligands are very similar. Please explain.

3. Why do authors use the frontier orbitals from the DFT-optimised geometries to explain the electronic transitions obtained by TD-DFT? It is rational to use the energies and frontier orbitals representation obtained from TD-DFT calculations in the point of view of the discussion about the nature of transitions.  For example, the low values of the f –oscillator demonstrates the ineffective excitation channels, correlating with the low absorbance (and absence of any excitation bands in the solution). These transitions do not participate in electronic transitions and emissions.  Addition information about the nature (transitions) of the emission observed is suggested being given.

3. Check the excitation in DMSO in fig.  5 for 1b.

4. It is unfortunate that the lifetimes have not been measured. It really could help not only demonstrate the phosphorescence or fluorescence nature but also to discuss the transitions of the emission observed.

Author Response

Dear reviewer,

thank you very much for evaluating our manuscript. Please find attached our list of point-by-point responses. All changes in the manuscript are highlighted in yellow.

Sincerely,

AXEL KLEIN

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Unfortunately, the authors have made no attempt to rectify the problems with their DFT calculations. I do not agree with their statement that the choice of functional is arbitrary. It is well known that long-range corrections are required to describe CT excitations. Also, they state that they were unable to calculate emission spectra due to lack of wavefunction overlap. They are referring to vibrationally resolved emission spectra, however they could still calculate the 0-0 and vertical emission wavelengths, analyse the excited state geometry and the orbital transitions involved in the emission. All of this can be done with very little computational effort in a short space of time.

largely satisfactory

Author Response

Dear Reviewer,

thank you very much for your comments. Find attached our response letter.

Best wishes,

AXEL KLEIN

Author Response File: Author Response.pdf

Reviewer 2 Report

My questions were answered by the authors.

But I would like to know why the red emission spectrum in Figure 4. 1b stops at 625 nm and the black spectra only starts at 550 nm? The spectra should start and finish at a point in which the intensity is approximately zero.

Author Response

Dear Reviewer,

thank you very much for your comments.

Reviewer 2:

But I would like to know why the red emission spectrum in Figure 4. 1b stops at 625 nm and the black spectra only starts at 550 nm? The spectra should start and finish at a point in which the intensity is approximately zero.

Response: The spectra were cut from the noise that is observed before 550 nm for the black spectrum and after 625 nm for the red spectrum. Without this noise, the “look” is much better, while no information is missing.

Best wishes,

AXEL KLEIN

Reviewer 3 Report

The authors performed revision and answered to the all questions/suggestions. The paper could be published in its present form

Author Response

Dear Reviewer,

thank you very much for your comment.

Best wishes,

AXEL KLEIN

Round 3

Reviewer 1 Report

I am happy with the additional theoretical analysis.

mostly fine

Author Response

Dear reviewer,

thank you very much for your positive response.

Best wishes,

AXEL KLEIN

Reviewer 2 Report

I can not agree with the fact that “no information is missing”, The idea that “the “look” is much better,” it is not a reasonable reason to cut the spectra. If the spectra present a huge noise level the author should comment on why the noise level is so high. Is it due to a limitation of the experimental setup used for the measurements?

Author Response

Dear reviewer,

thank you very much for your comments. We have re-evaluated all spectra of compound 1b and found more suitable ones (with a minor noise problem). We hope that the spectra in Figure 4 are now acceptable.

Best wishes,

AXEL KLEIN

Round 4

Reviewer 2 Report

no