Exploring the electronic, optical, and bioactive properties for new modified fullerenes via molecular modeling

Surface decor of pure fullerene motifs is greatly impacted by COOH, NH2, and Li terminals. Using DFT, the electrical, vibrational, and optical characteristics of unadorned and decorated fullerenes are thoroughly examined. For suggested fullerenes, QSAR descriptors are met via the PM6 interface. Results indicated that C60–2Li might compete with current kesterite Cu2ZnGeSe4 solar cells, which have an efficiency of more than 14% and a band gap range of 1.5–1.7 eV. The C60-2Li can be a brand-new row of manufactured solar cells with exceptional efficiency. According to MESP contours, while additional COOH and NH2 retain the original nucleophilic additions, additive Li exhibits a blue shift in Fullerene electronegative behavior toward electrophilic adds. The C60–2NH2 is recognized as a possible bioactive substrate for drug delivery based on QSAR values. This paves the way towed multidisciplinary adoption for mentioned fullerene systems.


Introduction
Carbon based-nanomaterials such as carbon nanotubes (CNTs) (Ghosh et al. 2021;Sakki et al. 2022), graphene (Hadad et al. 2021), fullerenes (Puente Santiago et al. 2021;Waite et al. 2021) and nano-diamonds (Khan et al. 2021;Yu et al. 2021;Mydlova et al. 2022) have surprised 1 3 100 Page 2 of 13 researchers by their unbelievable behaviors and extendable potential applications. Carbon quantum dots (CQDs) (Wu et al. 2021b;Chao et al. 2021) (Isabella et al. 2001) (Sahraoui et al. 2001)are zero-dimensional quasi-spherical carbon-nanoparticles with very small sizes (1-10 nm) and relatively distinctive fluorescence properties. Graphene quantum dots (GQDs) are nano fragments of graphene with anomalous luminescence behaviors (Shin et al. 2021;Liu et al. 2021a;Kulyk et al. 2020). The nitrogen-doped graphene quantum dots (N-GQDs) have been used for the delivery and fluorescence tracking of doxorubicin. In fact, N-GQDs have lowered 10 times doses of the drug taken by patients to achieve ordinary-like therapeutic effect used in controlling cancer cell growth (Frieler et al. 2021). Also, new fabricated GQDs with humic acid have efficiently acknowledged for Cu + 2 ions detection ). In addition, a highly efficient optosensors have been developed using TiO 2 /GQDs composited with specified imprinted polymer for cefazolin detection (Chansud 2021). Many computational studies have made graphene quantum dots with metal complexes to improve their optical and non-optical characteristics to foresees more advanced potential applications for GQDs (Permatasari et al. 2021;Zhao et al. 2021;Chen et al. 2021;Ezzat et al. 2021). Recent molecular modeling researches have focused on constructing electrostatic potential maps (ESP) for proposed chemical compounds (El-Mansy and El-Nahass 2014; Bayoumy et al. 2021;Ibrahim et al. 2013;Ismail et al. 2013). In consequences, ESP becomes a popular tool to provide precise mapping for active functional sites (Bulat et al. 2010;Soliman et al. 2013;El-Nahass et al. 2013) that characterize predominant chemical addition attitude for various structures; either electrophilic or nucleophilic tendency. Several articles were presented previously involve the various definitions of molecular surface (Bayoumy et al. 2020a;Bayoumy et al. 2020c;El-Mansy et al. 2020a;El-Mansy et al. 2020b). One of the common definitions considers MESP maps as the outer area surrounding a chemical structure rising from a group of intersected spheres, whereas their centers are aligned with the nucleus of each species (Connolly 1983;Dunitz et al. 2000;Arteca et al. 1988;Francl et al. 1984); these assumed spheres are produced from forces named Van der Waals radii of the interested atoms (Bondi 1964). On the other side, MESP maps were presented via Bader et al. (Bader et al. 1967(Bader et al. , 1987 as the external contour of electrons density ρ(r). Such term is the most popular relative to the first one because it includes more informative details on the chemical properties of the investigated chemical structures, e.g. lone pair electrons, σ-holes presence, and many more. These external contours have been always ensured to represent nearly 95-98% of the details regarding electronic density of some structures (Geesi et al. 2021;Wu et al. 2021a;Chai et al. 2021). The mapped electrostatic potential V(r) of a structure had been recognized as a major portion in controlling its reactive attitude. Recent physicochemical characteristics aided through QSAR technique have been an efficient tool in mapping pharmaceutical and biological applications for various molecules Rosa et al. 2021;Alves et al. 2021;Wu et al. 2021c;Chatterjee and Roy 2021). The aim of intended study is to investigate the effect of COOH, NH 2 as well as Li substituents on electronic, vibrational, and optical properties of fullerene. Moreover, QSAR descriptors are investigated to foresee medicinal applications as well. The Modified fullerenes are expected to offer new potential devices for solar cell and memory switches technology. et al. 2021; Liu et al. 2021b) and then both IR and Raman spectra are reproduced as well. Also, QSAR descriptors are computed via semiempirical PM6 interface (Wen et al. 2021;Alotaibi et al. 2021) provided by implemented SCIGRESS 3.0 (Badry et al. 2021;Elfiky,Azzam 2020) software at the same facility. Some QSAR indices are highlighted as total energy (E), resultant formation heat (FH), ionization potential (IP), partition coefficient (logP), molar-refractivity (M R ), molecule weight (M W ), and finally polarizability (P).

Building model molecules
Fullerene is studied as a model molecule as indicated in Fig. 1, at sites 4 and 5 one bond is broken then two units of COOH, NH 2 as well as Li are attached as complex through 4 and 5 atoms of fullerene forming C 60 -2COOH, C 60 -2NH 2 and C 60 -2Li, respectively as indicated in Fig. 2a-c.

Frontier molecular orbitals (FMOs) analyses
As structural reactivity and reactants selective pathways are clarified by FMOs theorem  Table 1 for studied configurations. Results showed that designed C 60 -2Li configuration have high total dipole moment (12.74 Debye) and optical energy gap (1.41 eV). The decorated C 60 -2Li solar efficiency may compete recent kesterite Cu 2 ZnGeSe 4 solar cell which have band gap range as 1.5-1.7 eV and efficiency > 14% (Khelifi et al. 2021). Figure 3 represent HOMO/ LUMO offsets for designed C 60 configurations at B3LYP/6-31G(d,p).

IR and Raman analyses
Both calculated IR and Raman wavenumbers and the corresponding assignments for designed C 60 configurations are collected in Table 2. Computed IR and Raman spectra for proposed C 60 configurations at B3LYP/6-31G(d,p) in Fig. 4. Results showed that more indexed peaks have been recorded in C 60 -2Li configuration due to its large reactivity (TDM = 12.74 Debye) and lower band gap offset (1.41 eV). The assignments are briefly disused as the following: The O-H and N-H stretch modes are observed in the region 3400-3800 cm −1 (Branca et al. 2016;Karimi-Maleh et al. 2021). The O-H stretch for C 60 -2COOH is observed at 3746 cm −1 for both IR and Raman spectra. The O-H plane-in bend for C 60 -2COOH is noticed at 1194 cm −1 for both IR and Raman pattern. While O-H Plane-out bend for C 60 -2COOH is detected at 712 and 624 cm −1 for IR and Raman charts, respectively.
The N-H stretch for C 60 -2NH 2 is seen at 3572 and 3482 cm −1 in IR and Raman spectra, respectively. The N-H plane-in bend for C 60 -2COOH is assigned at 1098 and 1135 cm −1 Fig. 2 Model molecules for fullerene-2X whereas a-x = 2COOH; b-x = 2NH 2 and C-X = 2Li for IR and Raman pattern, respectively. Whereas N-H Plane-out bend for C 60 -2COOH is detected at 893 and 795 cm −1 for IR and Raman charts, respectively. The C = O and C = C stretch modes are scanned in spectral range 1850-1300 cm −1 (Dos Santos et al. 2021;Lin et al. 2021;Zhou et al. 2021). The C = O stretch for C 60 -2COOH is observed at 1828 cm −1 for both IR and Raman spectra. The Original C = C stretch for C 60 is found at 1436 and 1617 cm −1 for IR and Raman, respectively. The C = C stretch for C 60 -2COOH is seen at 1330 and 1609 cm −1 in IR and Raman, respectively. The C = C stretch for C 60 -2NH 2 is recorded at 1495 and 1603 cm −1 in IR and Raman plots, respectively. The C = C stretch for C 60 -2Li is indexed at 1607 and 1567 cm −1 in IR and Raman, respectively.
The C-C stretch is observed at 969 and 1072 cm −1 for C 60 -2COOH at IR and Raman peaks, respectively. Similarly, The C-C stretch is observed at 965 and 988 cm −1 for C 60 -2Li in IR and Raman, respectively.
The C-O plane-in bend is observed at 665 and 560 cm −1 for C 60 -2COOH at IR and Raman peaks, respectively. The C-N plane-in bend is observed at 599 cm −1 for C 60 -2NH 2 in both IR and Raman, respectively. Finally, The C-Li plane-in bend is observed at 593, 558 cm −1 for C 60 -2LI in IR and Raman, respectively.

Molecular electrostatic potential (MESP)
Geometry optimization calculations are performed for fullerene structure as well as its proposed derivatives to show their MESP distribution. Generally, MESP maps appear in several color gradients indicating regions of different electronegativity. These colors always go from red to dark blue spectrum, the red one corresponds to sites of extreme negativity while the blue is for positive regions. The full colors range is red, yellow, green, light blue and dark blue representing the most negative and most positive, respectively. MESP colors are always attributed, in some way, to the electronegativity of the shared atoms where atoms having high electronegativity will appear in red at bonding to others of lower electronegative values. Therefore, presence of species of similar electronegativity creates narrow color distribution and green color may be predominant. Figure 5 shows the calculated MESP maps of fullerene and its suggested derivatives. The illustrated MESP maps are characterized by the presence of some colors of the previously mentioned ones. A spherical red elliptical region can be noticed obviously at the central region of fullerene structure that attributed previously (Bayoumy et al. 2020b) for the strong electron delocalization resonance for multiple benzene moieties forming fullerene. Such light blue color is the main color in all proposed derivatives especially for C 60 -2Li in which Li addition affect significantly both circumference and red ellipse inside fullerene ball, that appear in very faint red flag. Small dark blue regions appear as well around the additive Li atoms. However, additive COOH and NH 2 groups has no noticeable impact on this red elliptical sphere inside fullerene ball. New mapped regions arising upon additive COOH. Firstly, a yellow region around O atoms indicating the withdrawing electrons quarrel occurs between COOH group and fullerene sphere. Toward each other. Presence of yellow instead of red color around O represent success of fullerene to attract electrons from O. Dark blue color appears in the vicinity of terminal H atoms of COOH groups due to electrons attraction via O atoms. Similarly, MESP map of C 60 -2NH 2 has the same pattern of C 60 -2COOH, however the yellow color around N atoms is light not dark which may be due to that O is more electronegative than N atom. Eventually, Additive Li possesses a blue shift in Fullerene electronegative behavior towards electrophilic additions whereas additive COOH and NH 2 maintain the same intrinsic nucleophilic additions.

QSAR analyses
QSAR technique provides a clear and extensive scheme for potential biological sharings of target biostructures. QSAR has been acknowledged as the most valuable tool for mapping structures bioactivities (Shylaja et al. 2021;Ojha et al. 2021). Table 3 lists the PM6 QSAR characters such as overall energy (E) (stability index), resultant formation heat (FH) (enthalpy change during a chemical formation process), ionizating-potential (IP), partitioncoefficient (logP), molar-refractivity (M R ), molecule-weight (M W ), and polarizability (P).
Results showed that additive Li has no significant impact on fullerene stability whereas both additives NH 2 and COOH are highly lower its stability. The FH for C 60 -2COOH, Fig. 5 Calculated MESP maps for a C 60 , b C 60 -2COOH, c C 60 -2NH 2 and d C 60 -2Li Page 9 of 13 100 C 60 -2NH 2 and C 60 -2Li are 616.475, 783.445 and 778.903 kcal mol −1 , respectively. The electric conductivity is improved a little bit for both C 60 -2NH 2 and C 60 -2COOH than pristine fullerene. Unfortunately, the lack in C 60 -2Li conductivity may be attributed to Li mono-valence nature. Regarding log P values, both pristine and decorated fullerenes ensure a dominant hydrophobic character. The C 60 hydrophobicity seems to be down grading upon additive 2COOH, 2Li, and 2NH 2 as C 60 > C 60 -2COOH > C 60 -2Li > C 60 -2NH 2 . The low C 60 -2NH 2 hydrophobic character emphasize that more attached amino antennae would drag the original fullerene towards improved bioactivities. Molar-refractivity of C 60 has improved positively by additive 2COOH and 2NH 2 in contradict to 2Li. Polarizability index for pristine fullerene has improved slightly by additive 2COOH, 2NH 2 , and 2Li groups. Hereby, the C 60 -2NH 2 is acknowledged as potential bioactive substrate for drug delivery.

Conclusion
All electronic, spectroscopic and optical features for both pristine and decorated fullerenes via subsequent terminals (COOH, NH 2 , Li) are completed by G09W (BELYP 6-31G(d,p)) interface. The predicted spectral (IR & Raman) charts for designed C 60 configurations are calculated considering desired functional group assignments at the same level. It is remarkable that Additive Li possesses a blue shift in C 60 electronegative behavior towards electrophilic additions. On the other hand, additive COOH and NH 2 maintain the same intrinsic C 60 nucleophilic additions. In Fact, C 60 -2Li have high total dipole moment (12.74 Debye) and band offset (1.41 eV). Hopefully, the upcoming decorated C 60 -2Li solar efficiency may compete recent kesterite Cu 2 ZnGeSe 4 solar cell which have band gap range as 1.5-1.7 eV and efficiency > 14%. Finally, The QSAR descriptors for functionalized C 60 showed that additive 2NH 2 implies bioactivities of pristine C 60 than 2COOH and 2Li terminals. The C 60 -2NH 2 is acknowledged as potential bioactive substrate for drug delivery.
Funding There is no funding received.

Data availability
The data will be available upon request.

Declarations
Conflict of interests I declare that the authors have no competing interests as defined by Springer, or other interests that might be perceived to influence the results and/or discussion reported in this paper.
Ethical approval This work is not applicable for both human and/ or animal studies.