Systematic Engineering of Properties of Graphene Quantum Dots by Aryl Amines

doi:10.21203/rs.3.rs-3233626/v1

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Systematic Engineering of Properties of Graphene Quantum Dots by Aryl Amines

https://doi.org/10.21203/rs.3.rs-3233626/v1

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Graphene quantum dots (GQDs) are becoming an efficient nanomaterial to control their optoelectronic properties by molecular engineering due to the advantages of tunability by size, shape, doping, and comparatively low degree of toxicity and a great extent of spatial confinement. Their bandgap can be tuned effectively by functionalization of their surface or edges with some specific groups. In the present study, systematic efforts have been made to tune the band gap and corresponding optical properties of the GQDs by functionalizing them with different aryl amine groups because of their potential for extremely strong and wide-ranging light absorption; these GQDs have also been demonstrated to be advantageous for photocatalysis. The absorption and fluorescence spectra have been investigated by employing density functional theory with Becke three parameters hybrid functional with Lee-Yang-Perdew (B3LYP) correlation functional as implemented in Gaussian 09 package. Functionalization with such aryl amine groups accounts for the decrement in band gap and shift of absorption spectra towards longer wavelength. Such narrow band gap GQDs are highly required for the applications such as photocatalysis and bio-imaging etc. The outcomes achieved in this way are highly consistent with other experimental findings.

Graphene quantum dots

aryl amines

density functional theory

photo catalysis

Two-dimensional graphene exhibits a zero bandgap due to the overlapping of conduction and valance bands at the Dirac point, which restricts its possible usage in electronic applications. But when the lateral attributes of graphene are diminished to the nano size, a band gap with non-zero value is introduced in a size-dependent manner resulting in graphene quantum dots (GQDs) [1, 2]. Owing to very interesting properties of GQDs like biocompatibility, high water solubility, non-toxic nature, and stable fluorescence, the GQDs have a wide range of applications in solar cells [3–5], light emitting diodes [6], bio-imaging and drug delivery [7, 8], sensing [9, 10], etc. But the challenges of obtaining a defined and favored bandgap for a given motive drastically affect the uses of GQDs. The variety of new GQDs is typically green or blue fluorescent, with a band gap between 2.2 to 3.1 eV [11, 12]. The low bandgap and corresponding longer wavelength fluorescent GQDs are extremely rare and desired for applications, especially for bio-imaging. This is because biological organisms have a background of scattered light in a short-wavelength region, therefore, don’t provide good image contrast. There are many strategies to tune the band gap of quantum dots, which includes the change in size, and shape [13, 14], the introduction of heteroatoms [15, 16], modifying their surfaces [17, 18], etc.

Since the band gap of GQDs depends on the surface area of the sp² region of GQDs and is found to be inversely proportional to it [19, 20]. This sp²-conjugated carbon network can be enlarged by functionalizing the GQDs with aromatic rings. In this work, a systematic approach is used to gradually reduce the band gap of GQD and produce a variety of different bandgap GQDs theoretically for the first time. The aryl amines (o-phenylenediamine (OPLD), 2,3-diaminonaphthalene (DNT23), 1,8-diaminonaphthalene (DNT18)) have been used to functionalize the GQDs because these groups enlarge the sp² region and these also contain an electron-withdrawing element (Nitrogen atom) which causes a significant reduction in the bandgap of GQDs. These GQDs have also been proven to be favorable for photocatalysis because they promise highly intense and extensive light absorption [11]. The absorption and photoluminescence spectra have been calculated by using density functional theory, and the outcomes so acquired are discovered to be in fair accord with the previously reported experimental conclusions.

The present investigation of structural, electronic, and optical properties of GQDs has been investigated by using the Gaussian 09 package [21]. The density functional theory (DFT) has been used to optimize the ground state of the QDs by using Becke three parameters hybrid functional with Lee-Yang-Perdew (B3LYP) correlation functional with 6-31G* basis set [22]. All the GQDs are relaxed to optimized geometry with all positive frequencies. Following optimization, the excited state predictions are performed utilizing time-dependent DFT in the geometry of the optimized ground state. The first 25 excited states are used for the calculation of the absorption and photoluminescence spectra. All the calculations are computed for the GQDs dispersed in the water employing the polarizable continuum model (PCM), considering that the PCM/TD-DFT approach has been proven to be effective in studying the excited states and optical properties [23]. GaussView (version 5) has been used as a visualization tool for the visualization of molecular orbitals [24]. Multiwfn has been used to plot the absorption and photoluminescence spectra [25].

First of all, the stability of the GQDs used for the present work has been checked. Following the stability check by figuring out the cohesive energy, the structural properties of the GQDs are discussed. The HOMO - LUMO molecular orbitals and their respective band have been calculated in this section. The optical properties, particularly absorption and photoluminescence spectra, have also been studied and have been used for estimating the QY of the respective GQD.

Structural Properties and Energetic Stability

Figure 1 displays all of the GQDs’ optimized structures. The C-C bond length of all these has been found to be in the range of 1.42–1.44 Å, which is in consonance with other reported results [26] while the bond length of the C-N bond has been estimated between 1.30–1.33 Å which verifies the fact that when an atom of smaller radius replaces the carbon atom, the bond length gets reduce [27].

It is well established that cohesive energy can be used to evaluate the stability of a structure. The structure’s stability is demonstrated by its possessing a negative cohesive energy value. Cohesive energy is defined as the variation between the energy of the entire system and the sum of the energy of their constituent atoms [28]. The cohesive energy of the presented GQDs has been calculated by using the Eq. (1):

$${E}_{cohesive}=\frac{{E}_{GQD}-{N}_{c}{E}_{c}-{N}_{N}{E}_{N} -{N}_{H}{E}_{H}}{{N}_{C}+{N}_{N}+{N}_{H}}$$

Where ${E}_{cohesive}$ represents the cohesive energy of the GQDs. ${E}_{GQD}$ represents the energy of the GQD, ${N}_{C}, {N}_{N}, \text{a}\text{n}\text{d} {N}_{H}$ represent the numbers of carbon, nitrogen, and hydrogen atoms in the structure. And, ${E}_{c}, {E}_{N}, \text{a}\text{n}\text{d} {E}_{H}$ represent the atomic energy of these atoms, respectively.

The cohesive energies of all the QDs have been shown in Table 1. Their negative value indicates that the structures of GQDs used for the calculations of the electronic and optical properties are stable.

Table 1

Cohesive energies of all the GQDs.
Quantum Dots	Pristine GQD	GQD-OPLD	GQD-DNT23	GQD-DNT18
Cohesive Energy (eV)	-6.83	-6.90	-6.89	-6.86

Electronic and Optical Properties

The difference between the HOMO and LUMO of the corresponding GQD has been utilized to calculate the optical band gap of that GQD. The calculated band gap and the corresponding change with enlarging the sp² region of C-atoms is indicated in Fig. 2.

The absorption and photoluminescence plots of all the GQDs are shown in Fig. 3. It is clear from the figure that the functionalization with aryl amine groups results in the red shift of the absorption and emission spectra. The emission peaks of GQD, GQD-OPLD, GQD-DNT23, and GQD-DNT18 are located at 306 (305), 585 (610), 640 (637), and 658 (652) nm, respectively and are in excellent concordance with the experimentally reported values indicated in brackets with these [29, 11]. The emission energy corresponding to these values are 4.05 eV, 2.11 eV, 1.93 eV, and 1.88 eV of these conjugated GQDs, which is a manifestation of the narrowing of the band gap. The presence of aryl amine groups decreases the emission energy and shifts it from the yellow to the red region, which is required for photocatalysis.

The observed red shift of the absorption and photoluminescence spectra can be explained by using the molecular orbital surfaces of the HOMO and LUMO. Therefore, to clearly understand this effect, the HOMO and LUMO of all the GQDs are plotted in Fig. 4. It is clear from Fig. 3 that the HOMO –LUMO of pristine GQDs have π bonding characteristics, but when aryl amine groups are attached to the GQD, LUMO orbital shows some σ-bonding characteristics, which cause a reduction in the band gap and corresponding shift in absorption and photoluminescence spectra towards longer wavelength. The HOMO-LUMO orbital surfaces of conjugated GQDs show some additional π bond properties than the pure GQD because of the conjugation with the aromatic ring, which also lowers the energy of π* orbital and results in narrowing the band gap.

In conclusion, this study illustrates a method for systematically engineering the optical and electronic properties of GQD. In particular, modifying GQDs with aryl amines to increase conjugated sp²-carbon systems reduces the GQD bandgap, which in turn increases PL wavelength primarily by decreasing the π* orbital. In principle, the bandgap of GQD can be precisely tuned simply by increasing the aromatic ring conjugated to pristine GQD. This conjugation shifts the emission energy of pristine GQD from 4.05 eV to 1.88 eV. With such exquisite bandgap engineering, GQDs can be precisely customized for specific applications. Additionally, these GQDs could also be utilized in bio-imaging because of the possibility of less scattering and better imaging contrast than the lower wavelength emitting GQDs.

Acknowledgements

Priya Rani thankfully acknowledges the funding received in the form of a University Research Scholarship. The authors gratefully acknowledge HPCC Panjab University Chandigarh for providing the Gaussian 09 Package and the Department of Physics, Guru Jambheshwar University of Science and Technology, Hisar, for providing the necessary computational facilities.

Rani, P., Dalal, R., Srivastava, S., Kumar, T.: Phys. Chem. Chem. Phys. 24, 26232 (2022)
Rani, P., Dalal, R., Srivastava, S.: Proc. 65th DAE SSPS, 55, 562–563 (2021)
Chatterjee, M., Nath, P., Kadian, S., Kumar, A., Kumar, V., Roy, P., Manik, G., Satapathi, S.: Sci. Rep. 12, 9061 (2022)
Kwon, W., Kim, Y.H., Kim, J.H., Lee, T., Do, S., Park, Y., Jeong, M.S., Lee, T.W., Rhee, S.W.: Sci. Rep. 6, 24205 (2016)
Areerob, Y., Oh, W.C., Hamontree, C., Nachaithong, T., Nijpanich, S., Pattarith, K.: Sci. Rep. 13, 7762 (2023)
Liu, Q., Sun, J., Gao, K., Chen, N., Sun, X., Ti, D., Bai, C., Cui, R., Qu, L.: Mater. Chem. Front. 4, 421–436 (2020)
Biswas, M.C., Islam, M.T., Nandy, P.K., Hossain, M.M.: ACS Mater. Lett. 3, 889–911 (2021)
Li, Z., Qi, G., Shi, G., Zhang, M., Hu, H., Hao, L.: Molecules. 28, 2363 (2023)
Kalkal, A., Kadian, S., Pradhan, R., Manik, G., Packirisamy, G.: Mater. Adv. 2, 5513–5541 (2021)
Lee, J., Park, M., Song, Y.G., Cho, D., Lee, K., Shim, Y.S., Jeon, S.: Nanoscale Adv. 5, 2767 (2023)
Yan, Y., Chen, J., Li, N., Tian, J., Li, K., Jiang, J., Liu, J., Tian, Q., Chen, P.: ACS Nano. 12, 3523–3532 (2018)
Tan, X., Li, Y., Li, X., Zhou, S., Fan, L., Yang, S.: Chem. Commun. 51, 2544–2546 (2015)
Rani, P., Dalal, R., Srivastava, S.: Appl. Nanosci. 12, 2127–2138 (2022)
Rani, P., Singh, R., Srivastava, S.: Materials Today Proceedings, 46, 5817–5822 (2021)
Feng, J., Dong, H., L. Yu., and, Dong, L.: J. Mater. Chem. C. 5, 5984–5993 (2017)
Rani, P., Dalal, R., Srivastava, S.: Phys. Scr. 98, 064004 (2023)
Feng, J., Guo, Q., Song, N., Liu, H., Dong, H., Chen, Y., Yu, L., Dong, L.: Diam. Relat. Mater. 113, 108264 (2021)
Rani, P., Dalal, R., Srivastava, S.: App. Sur. Sci. 609, 155379 (2023)
Zheng, X.T., Ananthanarayanan, A., Luo, K.Q., Chen, P.: Small. 11, 1620–1636 (2015)
Sk, M.A., Ananthanarayanan, A., Huang, L., Lim, K.H., Chen, P.: J. Mater. Chem. C. 2, 6954–6960 (2015)
Frisch, M., Trucks, G., Schlegel, H., Scuseria, G., Robb, M., Cheeseman, J., Scalmani, G., Barone, V., Mennucci, B.: G (2009). .Petersson, Gaussian 09, revision D, 01
Schumacher, S.: Phys. Rev. B. 83, 081417 (2011)
Riesen, H., Wiebeler, C., Schumacher, S.: J. Phys. Chem. A. 118, 5189–5195 (2014)
Dennington, R., Keith, T., Millam, J.: GaussView, version 5, Semichem Inc.: Shawnee Mission, KS (2009)
Lu, T., Chen, F.: J Comput. Chem. 33, 580–592 (2012)
Kim, S., Hwang, S.W., Kim, M.K., et al.: ACS nano. 6, 8203–8208 (2012)
park, H., Woo, D., Lee, J.M., Park, S.J., Lee, S., Kim, H.J., Lee, G.D.: Sci. Rep. 9, 18961 (2019)
Deb, J., Paul, D., Sarkar, U.: J. Phys. Chem. A. 124, 1312–1320 (2020)
Clar, E., Schmidt, W.: Tetrahedron. 34, 3219–3224 (1978)

No competing interests reported.

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Systematic Engineering of Properties of Graphene Quantum Dots by Aryl Amines

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Abstract

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Introduction

Computational Details

Results and Discussion

Structural Properties and Energetic Stability

Electronic and Optical Properties

Conclusion

Declarations

Acknowledgements

References

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