TD-DFT Approach Research Articles

Effect of Flavone and Isoflavone in the Triphenylamine-Based Sensitizers for Dye-Sensitized Solar Cell Applications: DFT and TD-DFT Approach

Several metal-free organic sensitizers have been designed for dye-sensitized solar cell applications. The effect of flavone and isoflavone in the triphenylamine sensitizers was investigated in the present work. The dyes with different donors are analyzed by density functional theory and time-dependent density functional theory. The various parameters such as geometry, electronic structure, highest occupied molecular orbital and lowest unoccupied molecular orbital, light harvesting efficiency and electronic absorbance spectrum of the designed sensitizers were analyzed. The absorption bands in the visible and near-Ultra Violet (UV) region are correlated to photoinduced electron transfer process. The effect of flavone on the triphenylamine donor retards the photo degradation of the dye. It gives hyperchromic and bathochromic shift in the dyes and it also acts as UV filters. Free energy change for electron injection and dye regeneration was calculated. The results show that the designed dyes may be an efficient sensitizer for DSSC applications.

Intermolecular interactions, spectroscopic and theoretical investigation of 4-aminoacetophenone

The molecular structure of 4-aminoacetophenone (PAAP) was determined by DFT calculations using different basis sets. The structural parameters, electronic properties and vibrational wavenumbrers of the optimized geometry have been determined. The vibrational wave-numbers of the fundamental modes of the title compound have been precisely assigned and analyzed and the theoretical results are compared with the experimental vibrations observing a very good correlation. TD-DFT approach was applied to assign the electronic transitions ob-served in the experimental UV-vis spectrum. The molecular electrostatic potential map was used to identify the possible electrophilic and nucleophilic sites. Natural bond orbital (NBO) analysis and atoms in molecules (AIM) approach are applied in order to quantify the relative strength of hydrogen bonding interactions and to account their effect on the stabilities of molecular arrangements. In addition, a detailed exploration of the intermolecular interactions that stabilizes the crystal packing has been performed by using the Hirshfeld surface analysis.  Â

Experimental and theoretical investingation on the effect of a spacer addition in zinc phthalocyanine-based anthracene properties

phthalocyanine-based anthracene (AnPc) and phthalocyanine-based triazole anthracene (AnPc-Tr) were characterized to emphasize the effect of adding spacer existing in AnPc-Tr on electronic, optical and electrical properties of AnPc. The structures of both molecules were confirmed by infrared spectroscopy, the obtained chart was compared to the theoretical calculation chart, Electronic properties were studied using the TD-DFT approach. The obtained results are harmonious with those obtained experimentally. Experimental and theoretical UV–Visible spectra showed six maxima, corresponding to the π-π* transitions of anthracene, B band, Q band and the dimerisation phenomenon. Current-Voltage characteristics showed typical diode trend where conduction is governed by space charge limited current without distributing traps. The dynamic AC electrical transport process was studied in function of temperature. It exhibited a hopping transport process according to an equivalent electrical circuit based on a resistance (Rs) in series with a resistance (Rp) which is parallel to a Constant Phase Element (CPE).

Methodological Survey of Simplified TD-DFT Methods for Fast and Accurate Interpretation of UV-Vis-NIR Spectra of Phthalocyanines.

A methodological survey of density functional theory (DFT) methods for the prediction of UV–visible (vis)–near-infrared (NIR) spectra of phthalocyanines is reported. Four methods, namely, full time-dependent (TD)-DFT and its Tamm–Dancoff approximation (TDA), together with their simplified modifications (sTD-DFT and sTDA, respectively), were tested by using the examples of unsubstituted and alkoxy-substituted metal-free ligands and zinc complexes. The theoretical results were compared with experimental data derived from UV–visible absorption and magnetic circular dichroism spectroscopy. Seven popular exchange-correlation functionals (BP86, B3LYP, TPSSh, M06, CAM-B3LYP, LC-BLYP, and ωB97X) were tested within these four approaches starting at a relatively modest level using 6-31G(d) basis sets and gas-phase BP86/def2-SVP optimized geometries. A gradual augmentation of the computational levels was used to identify the influence of starting geometry, solvation effects, and basis sets on the results of TD-DFT and sTD-DFT calculations. It was found that although these factors do influence the predicted energies of the vertical excitations, they do not affect the trends predicted in the spectral properties across series of structurally related substituted free bases and metallophthalocyanines. The best accuracy for the gas-phase vertical excitations was observed in the lower-energy Q-band region for calculations that made use of range-separated hybrids for both full and simplified TD-DFT approaches. The CAM-B3LYP functional provided particularly accurate results in the context of the sTD-DFT approach. The description of the higher-energy B-band region is considerably less accurate, and this demonstrates the need for further advances in the accuracy of theoretical calculations. Together with a general increase in accuracy, the application of simplified TD-DFT methods affords a 2–3 orders of magnitude speedup of the calculations in comparison to the full TD-DFT approach. It is anticipated that this approach will be widely used on desktop computers during the interpretation of UV–vis–NIR spectra of phthalocyanines and related macrocycles in the years ahead.

Syntheses, X-ray crystal structures of two new Zn(II)-dicyanamide complexes derived from H2vanen-type compartmental ligands: Investigation of thermal, photoluminescence, in vitro cytotoxic effect and DFT-TDDFT studies

Two new dicyanamide modulated zinc metal complexes [Zn4(LOMe)2(µ1-dca)2(µ1,5-dca)2] (1) and [Zn3(LOEt)2(H2O)(µ1-dca)(µ1,5-dca)] (2) have been synthesized using H2vanen-type compartmental ligands. Schiff base ligands and the complexes were characterized by means of elemental analyses, FT-IR, FT-Raman, UV–Visible, powder X-ray diffraction, TGA and fluorescence spectroscopy. Dicyanamide modulated Zn4/Zn3-nuclear metal complexes were structurally characterized by single crystal X-ray diffraction studies. In 1, the asymmetric Zn2-nuclear unit was ensembled with one fully deprotonated Schiff base ligand [LOMe]2− along with two dicyanamide ions where two structurally independent Zn(II) metal centers are found in the X-ray crystal structure. Single X-ray crystal structure confirmed the environment of Zn1 is distorted square pyramidal whereas Zn2 acquires distorted tetrahedral geometry. Unlike 1, in 2 three independent zinc metal centers have been identified as square pyramidal (Zn1), distorted trigonal bipyramidal (Zn2) and distorted tetrahedral (Zn3). 1 and 2 geometry were optimized using hybrid B3LYP functional with DGDZVP basis set to explain frontier molecular orbitals, molecular electrostatic potential and Hirshfeld surface (dnorm surfaces and 2D fingerprint plots). The electronic UV–Vis properties were determined by TD-DFT approach. The steady state and time-resolved fluorescence properties have been explored in DMSO solution. 1 and 2 exhibit bi-exponential decay and intra-ligand (π → π*) fluorescence behaviors with lifetimes in the range (2.45–5.71 ns). In addition, complexes solid-state and different solvent-dependent absorption and fluorescence spectra have been reported. Finally, the cytotoxic effect of the investigated dicyanamide complexes against breast cancer cell line (MCF7) shows promising results which makes them prospective complexes for anticancer medicament studies.

Designing dithienonaphthalene based acceptor materials with promising photovoltaic parameters for organic solar cells.

Scientists are focusing on non-fullerene based acceptors due to their efficient photovoltaic properties. Here, we have designed four novel dithienonaphthalene based acceptors with better photovoltaic properties through structural modification of a well-known experimentally synthesized reference compound R. The newly designed molecules have a dithienonaphthalene core attached with different acceptors (end-capped). The acceptor moieties are 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (H1), 2-(5,6-dicyano-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (H2), 2-(5-methylene-6-oxo-5,6-dihydrocylopenta[c]thiophe-4-ylidene)-malononitrile (H3) and 2-(3-(dicyanomethylene)-2,3-dihydroinden-1-yliden)malononitrile (H4). The photovoltaic parameters of the designed molecules are discussed in comparison with those of the reference R. All newly designed molecules show a reduced HOMO–LUMO energy gap (2.17 eV to 2.28 eV), compared to the reference R (2.31 eV). Charger transfer from donor to acceptor is confirmed by a frontier molecular orbital (FMO) diagram. All studied molecules show extensive absorption in the visible region and absorption maxima are red-shifted compared to R. All investigated molecules have lower excitation energies which reveal high charge transfer rates, as compared to R. To evaluate the open circuit voltage, the designed acceptor molecules are blended with a well-known donor PBDB-T. The molecule H3 has the highest Voc value (1.88 V). TDM has been performed to show the behaviour of electronic excitation processes and electron hole location between the donor and acceptor unit. The binding energies of all molecules are lower than that of R. The lowest is calculated for H3 (0.24 eV) which reflects the highest charge transfer. The reorganization energy value for both the electrons and holes of H2 is lower than R which is indicative of the highest charge transfer rate.

A combined experimental and computational studies of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione

ABSTRACTIn this work, we have recorded the Fourier Transform Infrared (FTIR) and Ultra-Violet Visible (UV–Vis) spectra of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione (C24H29NO3) in the spectral range 4000–400 cm−1 and 190–1400 nm, respectively. The thermo gravimetric (TG) analysis of the compound has been performed to check the thermal stability of the compound. The molecular geometry and complete vibrational spectra in the ground state are calculated by Hartree Fock (HF) and Density Functional Theory (DFT) using6-311G(d,p) basis set. The calculated vibrational harmonic frequencies are scaled using a proper scale factor, yielding a good agreement with the experimental data. Stability of the molecule arising from hyperconjugative interactions, charge delocalisation has been studied using natural bond orbital analysis (NBO). Mulliken charges, MEP mapping and temperature dependence on the thermodynamic properties in the optimised ground state have been calculated. UV–Visible spectrum of the molecule was calculated by using TD-DFT approach and the results were compared with the experimental one. We have calculated the several molecular parameters like ionisation potential, electron affinity, global hardness, electron chemical potential, electronegativity and global electrophilicity based on HOMO and LUMO energy values calculated at B3LYP/6-311G(d,p) level of theory. The calculated optimised structural parameters and vibrational wavenumbers are found to be in good agreement with the experimental results.

Synthesis, crystal structure, vibrational, optical properties, thermal analysis and theoretical study of a new Sn(IV) complex (C5H14N2)2[SnCl6]2·5H2O

In this study, a new organic-inorganic hybrid metal compound (C5H14N2)2[SnCl6]2·5H2O was crystallized at room temperature in the orthorhombic system (space group P212121) where the structure is determined by single crystal X-ray diffraction analysis. The examination of the structure shows the cohesion and stability of the atomic arrangement result from the establishment of N—H⋯Cl, O(W)—H(W)⋯Cl, N—H⋯O(W) and O(W)—H(W)⋯O(W) hydrogen bonds between 1-methylpiperazine-1,4-diium (C5H14N2)2+cations, isolated (SnCl6)2– anions and water molecules to form organic and inorganic layers parallel to the (a, c) plane and alternate along the b-axis. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D fingerprint plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The solid phase FTIR and FT-Raman spectra of this compound have been recorded in the regions 400–4000 and 100–500 cm−1, respectively. The vibrational frequencies were also predicted from the calculated intensities by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. Besides, the optical proprieties were investigated by UV-visible and photoluminescence spectroscopy studies in the region 200–700 nm and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. Moreover, this compound was characterized by thermal analysis between 300 and 500 K which revealing two phase transitions. Finally, X-ray photoelectron spectroscopy (XPS) analysis is reported to determine the degree of oxidation of tin in this compound and analyzing the surface chemistry of (C5H14N2)2[SnCl6]2·5H2O.

Novel and Convenient Synthesis of 2,7-Dialkyl-1,8-dihydro-as-indacenes­

A novel and convenient synthetic route towards dialkyl as-indacenes was achieved by alkylation of malonic esters with o-xylylene dibromide, to give the corresponding tetraester, and related diacid. The alkyl groups on the central benzene ring induce intramolecular, regiospecific cycloeliminations leading selectively to the diketones, the precursors of the corresponding 1,8-dihydro-as-indacenes. The structure of the 2,7-dimethyl-1,8-dihydro-as-indacene was determined by X-ray diffraction. The compound 2,7-diethyl-1,8-dihydro-as-indacene was characterized by means of 1H NMR, 13C NMR, FT-IR, UV/Vis measurements, electrochemistry, and elemental analysis. On the other hand, quantum chemical computations based on DFT methods were carried out to get insight into the molecular and electronic structures of the studied ligands. TDDFT approach was employed to calculate the vertical excitations and characterize the nature the UV/Vis absorption bands present in the experiments showing a very good agreement between experimental and calculated values. Finally, the reactivity of the compounds was assessed using the chemical potential (μ), chemical hardness (η), and electrophilicity (ω). Also, the electron-donating (ω–), electron-accepting (ω+), and the net electrophilicity powers (ω±) indexes were studied.

Tuning of some novel triphenylamine-based organic dyes for their potential application in dye-sensitized solar cells: A theoretical study

Here, we have studied the structural and optoelectronic properties of three series of TPA-based dyes viz. TPA-BBTA, TPA-BTA and TPA-NBT by using density functional theory (DFT). The study is performed by introducing different electron-donating and electron-withdrawing substituents to the TPA-based dyes. Based on the optimized geometries, the relative energy alignment of the frontier molecular orbitals (MO) has been analyzed. The photoelectron spectra and photovoltaic properties have also been investigated with the TDDFT approach. Our study reveals that the dyes substituted with the N(CH3)2 and OC2H5 groups will show maximum photovoltaic efficiencies along with low ΔH-L values compared to the other substituted dyes. As a result, these dyes will act as potential candidates for fabrication of dye sensitized solar cells (DSSCs).

Benzoylguanidines as Anion-Responsive Systems.

A series of benzoylguanidinium salts was prepared and the changes in UV/Vis spectra, triggered by the presence of anions, were investigated. All compounds undergo deprotonation with basic anions like dihydrogenphosphate and acetate in acetonitrile. The most pronounced spectral changes were obtained by deprotonation of N1 -benzoyl-N3 -(p-nitrophenyl) guanidinium chloride which shows the naked-eye visible color change from colorless to yellow. Measured pKa (BH+ ) in acetonitrile ranges from 12-16, which is comparable to the pyridinium cations. The proton transfer equilibria were also tested in acetonitrile/water mixture where all but the most acidic derivatives showed pKa (BH+ ) of 4-6 units which corresponds to apparent association constants of 104 -106 dm3 mol-1 . UV/Vis spectra of neutral and protonated forms were modelled by the TD-DFT approach using CAM-B3LYP and PBE0 functionals and compared to CC2 results. In the case of CAM-B3LYP, a parameter ω, defining amount of long-range exchange correction, was varied to achieve the best agreement with the experimental spectra. The optimized ω parameters are 0.10 a0 -1 for neutral benzoylguanidines and 0.20 a0 -1 for neutral nitrobenzoyl and protonated systems. The larger ω parameter in the latter is ascribed to more pronounced charge transfer character of the HOMO-LUMO transition - the one responsible for the lowest energy absorption band.

Experimental vibrational spectroscopy (FTIR and FT-Raman) of D-tryptophan and its anharmonic theoretical studies using density functional theory

The present work has explored the anharmonic vibrational spectroscopy of D-tryptophan (DTRP) with the help of the FTIR (4000-400 cm−1) and FT-Raman (4000-50 cm−1) spectra as well as DFT calculations. Anharmonic corrections are computed within the generalized vibrational perturbation theory (GVPT2) approach using the DFT/6-31G(d,p) quantum-mechanical model. The anharmonic frequencies calculated at GVPT2 level is found to be in remarkable agreement with experimental results and show a significant improvement over the harmonic approximation. The effect of intermolecular interaction (OH⋅⋅⋅⋅⋅O) on the geometrical parameters and vibrational frequencies are analyzed by the calculations on the dimeric structure of the title molecule. Further, the electronic spectrum in DMSO solvent has been analyzed using TD-DFT approach and it is compared with experimental results. Moreover, other molecular properties such as frontier molecular orbitals and nonlinear optical (NLO) properties are also investigated.

Performance analysis of $$\hbox {TiO}_{2}$$ TiO 2 -flavylium compound-based dye-sensitized solar cell (DSSC): a DFT–TDDFT approach

The computational study of flavylium compound consists of anthocyanin pigments: callistephin, Chrysanthemin, oenin and mytrillin, and anthocyanidin pigments: peonidin and petunidin dyes are used to identify the potential photosensitizer for dye-sensitized solar cell (DSSC). Density functional theory is adopted to study methoxyl and hydroxyl groups in six pigments. The computed results of six dyes show good oscillator strength (f), light harvesting efficiency, electron injection $$(\Delta G^\mathrm{{inject}})$$ and electron regeneration $$({\Delta } G^\mathrm{{regen}})$$ . The short-circuit current density $$({J}_{\mathrm{sc}})$$ , total reorganization energy $$({\uplambda }_{\mathrm{total}})$$ and open-circuit voltage $$({V}_{\mathrm{oc}})$$ were also discussed. Intermolecular charge transfer of six dyes was examined using frontier molecular orbital. However, Peonidin/Titanium dioxide system has shown a significant response in density of states. Hence, this study confirms peonidin dye can be used as a photosensitizer for DSSC applications.

Why Do Silver Trimers Intercalated in DNA Exhibit Unique Nonlinear Properties That Are Promising for Applications?

Our investigation of one-photon absorption (OPA) and nonlinear optical (NLO) properties such as two-photon absorption (TPA) of silver trimer intercalated in DNA based on TDDFT approach allowed us to propose a mechanism responsible for large TPA cross sections of such NLO-phores. We present a concept that illustrates the key role of quantum cluster as well as of nucleotide bases from the immediate neighborhood. For this purpose, different surroundings consisting of guanine-cytosine and adenine-thymine such as (GCGC) and (ATAT) have been investigated that are exhibiting substantially different values of TPA cross sections. This has been confirmed by extending the immediate surroundings as well as using the two-layer quantum mechanics/molecular mechanics (QM/MM) approach. We focus on the cationic closed-shell system and illustrate that the neutral open-shell system shifts OPA spectra into the NIR regime, which is suitable for applications. Thus, in this contribution, we propose novel NLO-phores inducing large TPA cross sections, opening the route for multiphoton imaging.

Structural and energetic properties of tautomeric forms of phosphonyl thioamides

Stable tautomeric forms in a series of phosphonyl thioamides have been studied using DFT methods. The molecules studied in this contribution present a phosphonyl group in β-position of the C–S bond connected to the amine group. The three most stable tautomeric forms with double bonds on either C=N, C=S, or adjacent C=C have been described, and their relative energies together with the transition barriers have been evaluated. In such molecules a six-member ring can be formed by a hydrogen bond between the oxygen of the phosphonyl group and the H–N bond of the thioamide. The tautomeric form involving a C=N double bond is found less stable than the two other forms by more than 10 kcal/mol. The transition barriers between the various tautomers are calculated to be as large as 40 kcal/mol for the isolated molecules, but less than 30 kcal/mol in the presence of one water molecule. Similar results are obtained with various substituents on the phosphorus or on the nitrogen atom. Electronic vertical spectra have been calculated using the TD-DFT approach for the three stable tautomeric forms in a series of six substituted phosphonyl thioamides, and it is found that the signature of each tautomer is sufficiently specific to allow for their clear identification in a mixture using UV–Vis spectroscopy.

Towards first-principles calculation of electronic excitations in the ring of the protein-bound bacteriochlorophylls

Modeling electronic excitation of bacteriochlorophyll (BChl) molecules in light-harvesting (LH) antennae from photosynthetic centers presents a challenge for the quantum theory. We report on a quantum chemical study of the ring of 32 BChl molecules from the bacterial core complex LH1-RC. Diagonal and off-diagonal elements of the excitonic Hamiltonian matrices are estimated in quantum chemical calculations of relevant fragments using the TD-DFT and CIS approaches. The deviation of the computed excitation energy of this BChl system from the experimental data related to the Qy band maximum of this LH1-RC complex is about 0.2 eV. We demonstrate that corrections due to improvement in modeling of an individual BChl molecule and due to contributions from the protein environment are in the range of the obtained discrepancy between theory and experiment. Differences between results of the excitonic model and direct quantum chemical calculations of BChl aggregates fall in the same range.

Binaphthyl-containing Schiff base complexes with carboxyl groups for dye sensitized solar cell: An experimental and theoretical study

We report on synthesis and characterization of binaphthyl containing Schiff base Ni(II), Cu(II), and Zn(II) complexes as promising photosensitizers for dye-sensitized solar cells (DSSC). Based on theoretical and experimental data, the possibility of their application in DSSC was confirmed. To our knowledge, we find dye performance of complex is steric and rigid structure widely spread to efficiency. The spatial and electronic structures of the complexes were studied by means of the quantum chemical modeling using DFT and TD-DFT approaches. The adsorption energies of the complexes on TiO2 cluster were calculated and appeared to be very close in value. The Zn(II) complex has the biggest value of molar extinction.

Inheritance of Photochromic Properties of Nitro-Substituted and Halogenated Spiropyrans Containing the Pyrrolidino[60]fullerene.

The photophysical and isomerization properties of hybrid molecular compounds that consist of photochromic nitro-substituted and halogenated spiropyran derivatives bonded to the surface of the [60]fullerene cage through the pyrrolidine bridge were investigated using various functionals and basis sets of TD-DFT and semiempirical quantum-chemical approaches. The role of nπ* states formed by the lone pairs of substituents in changing of the electronic structure and photochromic properties of spiropyran derivatives was evaluated. The Sππ(spiropyran) → intermediate nπ* states → Sππ(merocyanine) channel for phototransformation of the hybrid compound containing a nitro-substituted spiropyran moiety was established and compared with similar systems of halogenated spiropyrans attached to the [60]fullerene bulk where photoinduced isomerization does not process due to high probability of internal conversion from the excited electronic state localized on the spiropyran fragment to the states of the pyrrolidino[60]fullerene.

Fe-V sulfur clusters studied through photoelectron spectroscopy and density functional theory.

Iron-vanadium sulfur cluster anions are studied by photoelectron spectroscopy (PES) at 3.492 eV (355 nm) and 4.661 eV (266 nm) photon energies, and by density functional theory (DFT) calculations. The structural properties, relative energies of different structural isomers, and the calculated first vertical detachment energies (VDEs) of different structural isomers for cluster anions FeVS1-3- and FemVnSm+n- (m + n = 3, 4; m > 0, n > 0) are investigated at a BPW91/TZVP theory level. The experimental first VDEs for these Fe-V sulfur clusters are reported. The most probable ground state structures and spin multiplicities for these clusters are tentatively assigned by comparing their theoretical and experiment first VDE values. For FeVS1-3- clusters, their first VDEs are generally observed to increase with the number of sulfur atoms from 1.45 eV to 2.86 eV. The NBO/HOMOs of the ground state of FeVS1-3- clusters are localized in a p orbital on a S atom; the partial charge distribution on the NBO/HOMO localized site of each cluster anion is responsible for the trend of their first VDEs. A less negative localized charge distribution is correlated with a higher first VDE. Structure and steric effect differences for FemVnSm+n- (m + n = 3, m > 0, n > 0) clusters are suggested to be responsible for their different first VDEs and properties. Two types of structural isomers are identified for FemVnSm+n- (m + n = 4, m > 0, n > 0) clusters: a tower structure isomer and a cubic structure isomer. The first VDEs for tower like isomers are generally higher than those for cubic like isomers of FemVnSm+n- (m + n = 4, m > 0, n > 0) clusters. Their first VDEs are can be understood through: (1) NBO/HOMO distributions, (2) structures (steric effects), and (3) partial charge numbers on the NBO/HOMO's localized sites. EBEs for excited state transitions for all Fe-V sulfur clusters are calculated employing OVGF and TDDFT approaches at the TZVP level. The OVGF approach for these Fe/V/S cluster anions is better for the higher transition energies than the TDDTF approach. The experimental and theoretical results for these Fe/V/S cluster anions are compared with their related pure iron sulfur cluster anions. Properties of the NBO/HOMO are essential for understanding and estimating the different first VDEs for Fe/V/S, and comparing them to those of the pure Fe/S cluster anions.

Theoretical study on the optical and electronic properties of graphene quantum dots doped with heteroatoms.

The effects of four heteroatoms (B, N, P, and S) with three doping patterns on graphene quantum dots (GQDs) are systematically investigated using time-dependent density functional theory (TD-DFT). The absorption spectra and HOMO-LUMO gaps are quantitatively analyzed to study the correlations between the optical properties and heteroatom doping of doped GQDs. Heteroatom doping can endow GQDs with various new optical and structural properties, depending on the dopants and doping configurations. Compared with the absorption spectra of pristine GQD, both N and S surface doping demonstrate a slight blue shift, whereas B and P doping lead to a blue shift for edge-doped GQDs with heteroatoms in a pentatomic ring. The absorption process is investigated along with excited state analysis, which includes the density of state, natural transition orbital, and charge difference density. The results indicate that large radius atoms assist charge transfer in the excited state and play an important role in recombining the electron density distribution in the doped GQDs.