4,7-Bis(5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine
Round 1
Reviewer 1 Report
In this short not the authors present the synthesis and spectroscopic characterization of titled obtained in two steps starting from f 4,7-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine. For the 1st step, an optimisation process for the bromination reaction is described with 3 different reaction condition tested. Basic photophysical properties (absorption and emission spectra) azre also provided.
This short note is of potential interest for Molbank reader but some point need to be adressed before and extra experiment need to be performed.
1- All compound name should be checked: d and H should be systematically italicized (eg 4,7-bis( 5-(9-
hexyl-9H-carbazol-3-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine
2- l 26: OLEDs and OFETs are not s organic photovoltaic devices. I suggest to replace this term by optoelectronic devices.
3- l 46: remove "was"
4- l 48 lowering the yield of dibromo derivatives
5- Scheme 1: please add yield (or yield range for the 1st step)
6- l 65: the solvents should be specified and their polarity (for exemple according to Reichardt polarity scale). Instead of optical absorption spectra: electronic spectra.
7- The discussion about aborption solvatochromism is wrong. It is stated: "Since the wavelength of the absorption maximum shifts to the blue region of the spectrum from 582 to 665 nm with increasing medium polarity..." Having a look to Fig S9 we be observed a slight shifts of absorption band from around 580 in THF and DMSO) to around 590 in CHCl3... Nothing related to blue region and the 665 nm value is not coherent with experimental data. Moreover the red shift is not observed for the more polar solvent.
8- Fig S10: the spectra are normalized: no unit should be provided for y-axis: please remove a.u. and change the y-axis legend to "normalized emission intensity"
9- For such structure respect of Kasha rule (only one emission band) is expected: the observance of a second band should be explained and discussed.
10- The authors claimed that the title compound has potential application as active emitting layer in NIR OLED. At least their should measured emission quantum yield to prove that emission of this compound is not negligible.
11- l97 microTOF insted of micrOTOF
12- l116 and l130 mp>250 °C
13- Please select and attribute the main IR bands
14- Finally a curiosity: Why using Br2 complexed with dioxane? would "classical" Br2 be also efficient?
Author Response
Reviewer 1
The authors are grateful to the reviewer for a kind and highly professional review.
Point 1.
All compound name should be checked: d and H should be systematically italicized (eg 4,7-bis( 5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4- d]pyridazine)
Response from authors.
Corrected as suggested by the reviewer.
Point 2.
l 26: OLEDs and OFETs are not s organic photovoltaic devices. I suggest to replace this term by optoelectronic devices.
Response from authors.
Corrected as suggested by the reviewer.
Point 3.
l 46: remove "was"
Response from authors.
Corrected as suggested by the reviewer.
Point 4.
l 48 lowering the yield of dibromo derivatives
Response from authors.
Corrected as suggested by the reviewer.
Point 5.
Scheme 1: please add yield (or yield range for the 1st step)
Response from authors.
The yields are added to the Scheme 1.
Point 6.
l 65: the solvents should be specified and their polarity (for exemple according to Reichardt polarity scale). Instead of optical absorption spectra: electronic spectra.
Response from authors.
The Stokes shift between absorption and emission maxima in cm-1 has a linear dependence on orientation polarizability according to Lippert-Mataga equation (see, Lippert E. Spektroskopische Bestimmung des Dipolmomentes aromatischer Verbindungen im ersten angeregten Singulettzustand. Zeitschrift Für Elektrochemie. Ber. 1957, 61, 962e75). The polarity values were added in captions of Fig. 9 and 10 in SI (Δf=0.149 for CHCl3, Δf =0.210 for THF, Δf =0.274 for DMSO).
Point 7.
The discussion about aborption solvatochromism is wrong. It is stated: "Since the wavelength of the absorption maximum shifts to the blue region of the spectrum from 582 to 665 nm with increasing medium polarity..." Having a look to Fig S9 we be observed a slight shifts of absorption band from around 580 in THF and DMSO) to around 590 in CHCl3... Nothing related to blue region and the 665 nm value is not coherent with experimental data. Moreover the red shift is not observed for the more polar solvent.
Response from authors.
We have rephrased this sentence. In particular we replaced “shifts to the blue region” on “absorption maximum has a blue-shift from 585 nm for slightly polar CHCl3 to 567 nm for polar mediums such as THF and DMSO.“
Point 8.
Fig S10: the spectra are normalized: no unit should be provided for y-axis: please remove a.u. and change the y-axis legend to "normalized emission intensity"
Response from authors.
According to referee’s recommendation we have modified a figure S10.
Point 9.
For such structure respect of Kasha rule (only one emission band) is expected: the observance of a second band should be explained and discussed.
Response from authors.
As described in the literature [Misra, Ramprasad, and Shankar P. Bhattacharyya. Intramolecular charge transfer: theory and applications. John Wiley & Sons, 2018.] the energy levels model for many D-A dyes has a more complicated shape. There are at least two competitive energy migration pathways S1->S0 (locally excited state emission, LE state emission) and relaxation in intramolecular charge transfer state S1->S1(ICT) with a consequent fluorescence from the ICT state. In some cases, ICT emission appears in a short wavelength region in comparison with LE state emission [Wiedbrauk, S., Maerz, B., Samoylova, E., Reiner, A., Trommer, F., Mayer, P., Zinth, W., and Dube, H. (2016) J. Am. Chem. Soc., 138, 12219.]. We suggest a similar situation takes place in the case of the investigated dye. The corresponding discussion was added to the text.
Point 10.
The authors claimed that the title compound has potential application as active emitting layer in NIR OLED. At least their should measured emission quantum yield to prove that emission of this compound is not negligible.
Response from authors.
We have measured luminescence quantum yield as 10% in CHCl3 solution by the absolute method. This value corresponds to the efficiencies obtained for many organic NIR dyes. However, to clearly reveal the suitability of the material for electroluminescence purpose one need to fabricated test OLED structures. Now we are conducting some investigations in this field.
Point 11.
l97 microTOF insted of micrOTOF
Response from authors.
Corrected as suggested by the reviewer.
Point 12.
l116 and l130 mp>250 °C
Response from authors.
Corrected as suggested by the reviewer.
Point 13.
Please select and attribute the main IR bands
Response from authors.
The main IR bands are selected and partly attributed.
Point 14.
Finally a curiosity: Why using Br2 complexed with dioxane? would "classical" Br2 be also efficient?
Response from authors.
When carrying out the reaction under the action of molecular bromine in chloroform or DMF, the formation of significant amounts of polybromination products was observed.
Round 2
Reviewer 1 Report
The manuscript has been improved.
I suggest to remove the sentencel 69-70 "it can be concluded that the
long-wavelength component corresponds to the process of intramolecular charge transfer (ICT)": In fact in case of ICT a slight postive solvatochromism (ie: a slight red shift of absorption) is expected wen increasing polarity. It is however not unusual to have the most red shifted absortion in chlorinated solvant( CHCl3 or DCM)
l80 CHCl3
Author Response
Reviewer 1
The authors are grateful to the reviewer for a kind and highly professional review.
Point 1.
I suggest to remove the sentence l 69-70 "it can be concluded that the long-wavelength component corresponds to the process of intramolecular charge transfer (ICT)": In fact in case of ICT a slight postive solvatochromism (ie: a slight red shift of absorption) is expected wen increasing polarity. It is however not unusual to have the most red shifted absortion in chlorinated solvent (CHCl3 or DCM)
Response from authors.
Corrected as suggested by the reviewer.
