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Recently, the crystal structures and electrochemical properties of the isomers (Sc2S "trapped" in C82) have been reported, in which the Sc2S is located inside the different positions of the C82 cage. In the present work, three isomers of endohedral metallofullerenes Sc2S@C3v(8)-C82 (A, B, and C) have been designed to explore the effect of the position of Sc2S on their interaction energies and nonlinear optical properties. Among three isomers, the Sc2S is located in different positions of the C82 cage: the angles of Sc-S-Sc in A, B, and C are 104.9, 114.8, and 115.7°, respectively. Furthermore, the analysis of natural bond orbital (NBO) charge indicates that the electron-transfer is from the Sc2S to the adjacent carbon atoms of the C82 cage. The interaction energy of B is the smallest among three isomers which is -226.2 kcal mol(-1). It was worth mentioning that their first hyperpolarizabilities (β tot) were studied, we found that their β tot values were related to the positions of Sc2S: C (2100) > B (1191) > A (947 au). We hope that the present work can provide a new strategy to promote the nonlinear optical properties of endohedral metallofullerenes by changing the positions of the encapsulated molecular. Graphical abstract Three isomers of endohedral metallofullerenes Sc2S@C3v(8)-C82 (A, B, and C) have been designed to explore the position effect of Sc2S on the interaction energies and nonlinear optical properties. Among three isomers, the Sc2S in B has the most stable position. Significantly, the first hyperpolarizability is related to the position of Sc2S inside the C82 cage, which provides a novel strategy to enhance the first hyperpolarizability by the Sc2S revolving inside the C82 cage.

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72? To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (βtot). The βtot follows the order of 1174 au (Y2O@C72) ≈ 1179 au (Sc2O@C72) > 886 au (Y2S@C72) ≈ 864 au (Sc2S@C72) > 355 au (C72). This indicates that the βtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger βtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the βtot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance.

Stimulated by the recent isolation and characterization of C₅₆Cl₁₀ chlorofullerene (Tan et al., J Am Chem Soc 2008, 130, 15240), we perform a systematic study on the geometrical structures, thermochemistry, and electronic and optical properties of C₅₆X₁₀ (X = H, F, and Cl) on the basis of density functional theory (DFT). Compared with pristine C₅₆, the equatorial carbon atoms in C₅₆X₁₀ are saturated by X atoms and change to sp³ hybridization to release the large local strains. The addition reactions C₅₆ + 5X₂ --> C₅₆X₁₀ are highly exothermic, and the optimal temperature for synthesizing C₅₆X₁₀ should be ranged between 500 and 1000 K. By combining 10 X atoms at the abutting pentagon vertexes and active sites, C₅₆Cl₁₀ molecules exhibit large energy gaps between the highest occupied and lowest unoccupied molecular orbitals (from 2.84 to 3.00 eV), showing high chemical stabilities. The C₅₆F₁₀ and C₅₆Cl₁₀ could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states is also calculated, which suggest that the frontier molecular orbitals of C₅₆X₁₀ are mainly from the carbon orbitals of two separate annulene subunits, and the contributions derived from X atoms are secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C₅₆X₁₀ are calculated by means of time-dependent DFT and finite field approach, respectively. Both the average static linear polarizability <α> and second-order hyperpolarizability <γ> of these compounds are larger than those of C₆₀ due to lower symmetric structures and high delocalization of π electron density on the two separate annulene subunits.

ITIC-series nonfullerene organic photovoltaics (NF OPVs) have realized the simultaneous increases of the short-circuit current density (JSC) and open-circuit voltage (VOC), called the positive correlation between JSC and VOC, which could improve the power conversion efficiency (PCE). However, it is complicated to predict the formation of positive correlation in devices through simple calculations of single molecules due to their dimensional differences. Here, a series of symmetrical NF acceptors blended with the PBDB-T donor were chosen to establish an association framework between the molecular modification strategy and positive correlation. It can be found that the positive correlation is modification site-dependent following the energy variation at the different levels. Furthermore, to illustrate a positive correlation, the energy gap differences (ΔEg) and the energy level differences of the lowest unoccupied molecular orbitals (ΔELUMO) between the two changed acceptors were proposed as two molecular descriptors. Combined with the machine learning model, the accuracy of the proposed descriptor is more than 70% for predicting the correlation, which verifies the reliability of the prediction model. This work establishes the relative relationship between two molecular descriptors with different molecular modification sites and realizes the prediction of the trend of efficiency. Therefore, future research should focus on the simultaneous enhancement of photovoltaic parameters for high-performance NF OPVs. [ABSTRACT FROM AUTHOR]

A hot exciton model is a widely accepted mechanism for the generation of photocurrent in organic bulk-heterojunction solar cells, in which the charge is transferred from the high-energy Frenkel exciton state (FE state) of the donor to the low-energy charge transfer states (CT states) and then is further separated into free charges. However, the FE state energy of the acceptor (FEA state) is usually lower than the values of CT states, which could hinder the pathway of efficient charge transfer from the FEA state to CT states. In order to take full advantage of this pathway, in this study, acceptor molecule 1 which breaks the Kasha's rule was selected to constitute the donor/acceptor (D/A) interface with donor molecule PTB7-Th. The density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) calculations focusing on the charge transfer mechanism were carried out to verify our supposition. The results indeed show higher energy in the FEA state than the lowest CT states and enhanced charge transfer contribution (about 90%), which implies the realization of this additional pathway. Meanwhile, based on acceptor molecule 1, molecules 2–6 were designed by introducing different functional groups with the aim of enhancing the open circuit voltage (VOC) and photo-absorption ability while maintaining the advantage of the higher FE state energy, which demonstrates the improvement in hole and electron generation efficiency to some extent. Therefore, this study may provide a good strategy for designing new non-fullerene acceptors for organic solar cells (OSCs). [ABSTRACT FROM AUTHOR]

An investigation of C36Xn (X=F,Cl,Br; n=2,4,6,12) formed from the initial C36 fullerene with D6h symmetry has been performed using the MP2 theory. Their equilibrium structures, reaction energies, strain energies, lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO-HOMO) gap energies, and aromaticities have been studied. The calculation results showed that those addition reaction were highly exothermic and C36Xn were more stable than C36. Moreover, from the view of thermodynamics it should be possible to detect C36X6. The LUMO-HOMO gap energies of C36Xn were higher than D6hC36 and the redox characteristics of C36Xn were weaker comparing to D6hC36. The analyses of π-orbital axis vector indicated that the chemical reactivity of C36 was the result of the high strain, and the nucleus independent chemical shifts research showed that the stabilities of the C36X6 were correlative with the conjugation effect. [ABSTRACT FROM AUTHOR]

• A comparation between P3HT and PDCBT with a tiny structure difference were investigated based on MD simulations and DFT calculations in non-fullerene OSCs. • V OC , absorption spectra, and the hole mobility which is in relation to the ability of charge transport were researched in depth. • By considering both of electron and hole transfer processes, the interface CS/CR rates were calculated. The PDCBT shows much better performance than P3HT in non-fullerene organic solar cell although the former only replaces hexyl by alkoxycarbonyl group compared with the latter. In this work, we will focus on this tiny difference in structure and huge difference in performance between these two polymers from theoretical perspective. Thus we present a comparative study based on the dependent/time-dependent density functional theory (DFT/TDDFT) calculations and molecular dynamic (MD) simulations. The results reveal that PDCBT not only possesses lower molecular orbital energy levels which leads to the increasement of the open circuit voltage (V OC), but also exhibits better planarity and larger hole mobility than P3HT. In particular, comparing with P3HT system, PDCBT system also displays the higher charge separation rate and smaller charge recombination rate both in hole transfer and electron transfer process at the interface, which promote the enhancement of short-circuit current density. Therefore, this work provides a fundamental understanding of the prominent influence of the replacement of hexyl group by alkoxycarbonyl in P3HT on the cell performance and also provides some theoretical guidance for further optimization of donor materials in non-fullerene organic solar cells (OSCs). [ABSTRACT FROM AUTHOR]

In this work, three complexes C59Co, C59Rh and C59Ir are devised by the transition metals (Co, Rh and Ir) doped into fullerenes to study the structure-property relationships of the heterofullerenes. Results show that the natural population analysis (NPA) revealed substituting one carbon atom arouse an apparent charge transfer, which can be proved by the strong electron density transfer from SOMO to LUMO. Significantly, the first hyperpolarisability (βtot) were investigated by BHandHLYP and CAM-B3LYP and got the same trend in βtot value: C59Ir > C59Rh > C59Co. Further, two-level expression was also provided to test the βtot values of C59Co, C59Rh and C59Ir. We hope our work can offer a new idea for designing high-performance NLO materials based on metal-doped fullerene. Density function theory can provide a precise calculation on the first hyperpolarisability of metal-doped fullerenes. In this work, compared to traditional fullerene, transition metal-doped fullerenes show spectacular NLO response, the three heterofullerenes: C59Co, C59Rh and C59Ir are designed to explore NLO materials. This article takes a look at initial reasons why they possess evident first hyperpolarisabilities and outlines a step to keep research on new NLO materials. [ABSTRACT FROM AUTHOR]

Two non-fullerene acceptors with a three-dimensional structure based on the reported DBFI-T molecule (an arylenediimide-containing system) were theoretically modelled to study their performance as acceptor materials in organic solar cells (OSCs). Many performance indices were employed to judge the molecules designed by us on the basis of density functional theory/time-dependent density function theory (DFT/TDDFT). Compared with DBFT-T, the modelled molecule 2 has a larger density of states in the lowest unoccupied molecular orbitals and more low lying excited states in the anion, which greatly favors the charge separation process in OSCs. The comparison of charge separation/recombination rates (kCS/kCR) evaluated by considering the influence of low-lying excited states at the PSEHTT (donor)/acceptor interface suggests that molecules 1 and 2 have a higher short-circuit current density (Jsc) than DBFI-T, since they have higher kCS and lower kCR. Moreover, many other important parameters, such as the open circuit voltage, energetic driving force and absorption spectrum were also provided, which further illustrates the efficacy of molecules 1 and 2 in OSCs. [ABSTRACT FROM AUTHOR]

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72 To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (βtot). The βtot follows the order of 1174 au (Y2O@C72) 1179 au (Sc2O@C72) > 886 au (Y2S@C72) 864 au (Sc2S@C72) > 355 au (C72). This indicates that the ßtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger βtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the tot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance. [ABSTRACT FROM AUTHOR]

A systematic density functional study was performed on the structures and bonding features in a homologous metal-metal (M-M) host-guest series M2@C50X10 (M = Zn, Cd, Hg; X = CH, N, B). Calculations indicated that D5 d conformers are energy minima for Zn2@C50X10 (X = CH, N) and Cd2@C50X10 (X = CH, N, B), whereas Zn2@C50B10 has no imaginary frequency with the lowered C2 h symmetry. Among these hybrid fullerene-metal complexes, those with dizinc and dicadmium guests adopt η5/η5 coordination, except for an η2/η2 case in C2 h-Zn2@C50B10, to meet appropriate interactions between the metal atom and cage; and the η1/η1 coordination mode can only be satisfied in just one (Hg2@C50N10) of the complexes with Hg-Hg guests, regardless of the enforced coordination surroundings. The nature of metal-cage interactions between M22+ and C50X102- moieties and M-M bonds have been analyzed by means of the topological properties of electron densities and energy-partitioning methods, and results suggest that the two types of interactions are almost similar to those in their M2(C5H5)2 counterparts. [ABSTRACT FROM AUTHOR]

To maximize the efficiency of heterojunction organic photovoltaics (HJOPVs), it is imperative to increase not only the open-circuit voltage ( V) but also the short-circuit current ( I). Therefore, it is desirable to find an organic acceptor material that possesses a higher lowest unoccupied molecular orbital (LUMO) level for higher V and can absorb photons in the solar spectrum efficiently for larger I. In this paper, in comparison with the typical donor poly(3-hexylthiophene) (P3HT) and acceptor [6,6]-phenyl-C-butyric acid ester ([60]PCBM), the geometries, electronic structures, absorption spectra, and transport properties of a series of organic compounds containing 9,9′-bifluorenylidene (9,9′ BF) were systematically investigated using density functional and the semiclassical Marcus charge transfer theory calculation to evaluate their potential severing as acceptor. Our results indicate that the absorption spectra of 99′ BF derivatives have better overlap with the solar spectrum than those of [60]PCBM, and higher LUMOs result in a significant enhancement of V when they are used in HJOPVs with P3HT as donor materials. On the other hand, these compounds own higher electron carrier mobilities comparing with [60]PCBM. The study also demonstrates that the H-shaped compounds based on the 99′ BF backbone possess good photophysical and charge transport properties, can be promising organic semiconductor for heterojunction photovoltaics. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory (DFT) calculations on the finite clusters of perfect and defective armchair (5,5) and zigzag (9,0) single-walled carbon nanotubes (SWCNTs) terminated by hydrogen atoms and fullerene hemispheres were carried out at the B3LYP/6-31G* level of theory. The most negative potentials and their positions, reactivity index in SWCNTs with no defects, with a carbon ad-dimer (CD) defect and with a Stone–Wales (SW) defect were compared. The results indicate that the CD defective sites in both the open-ended and cap-ended SWCNTs are chemically more reactive than the SW defective sites and the perfect sites. In contrast, the SW defect in the cap-ended armchair (5,5), zigzag (9,0) as well as the open-ended armchair (5,5) SWCNTs has slight effect on the molecular electrostatic potential (MEP) compared with the MEP of pristine SWCNTs; the SW defective sites become more reactive than the perfect sites for open-ended zigzag (9,0) SWCNT. [ABSTRACT FROM AUTHOR]

ABSTRACT: Stability and electronic property calculations are performed systematically based on density functional theory at the B3LYP/6-31G(d) level for Td C28 fullerene and exohedral fluorine and trifluoromethyl derivatives C28F4–n(CF3)n (n = 0,1,2,3,4). All the exohedral derivatives that are on the potential energy surfaces are kinetically stable with large HOMO-LUMO gaps. Further investigations show that binding energies of C28F4–n(CF3)n (n = 0,1,2,3,4) molecules are positive, suggesting they are thermodynamically stable. An analysis of the π-orbital axis vector indicates the high strain in Td C28 cage could be greatly released by fluorine and trifluoromethyl decorations. Mulliken charge analysis reveals that adding different electron groups to the Td C28 cage can cause remarkably different charge populations. In addition, from the ionization potential and electron affinity investigations, the C28F4–n(CF3)n (n = 0,1,2,3,4) molecules manifest weak redox properties. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Abstract: Three different nanotube structures, armchair, zigzag and wurtzite, were studied using B3LYP/6-31G(d) for carbon, BN, AlN and GaN nanotubes, respectively. Our calculations found that AlN and GaN can implausibly form the usual tubular morphologies of carbon and BN nanotubes. The same conclusion was confirmed based on analyzing the different configurations of benzene, borazine, and the analogies of the hexagonal Al3N3H6 and Ga3N3H6 at the same level of calculations. [Copyright &y& Elsevier]

A 3D chiral nanoporous coordination framework consisting of homochiral nanotubes assembled from octuple helices with a 19.4 Å by 22.4 Å aperture is formed by the parallel alignment of eight infinite helical chains. [ABSTRACT FROM AUTHOR]

Theoretical predictions of macroscopic performance (power conversion efficiencies [PCEs]) and experimental analyses for microscopic material (conformation) have always urged for organic photovoltaics. A series of acceptors based on multi‐conformation bistricyclic aromatic enes core have been designed. The results suggested that A4‐2, A5‐2, and T4‐2 show the full folded conformation, fitting, and exhibiting advantageous properties of various parts for acceptors effectively, thus getting high VOC and JSC (kCS/kCR exceeds 1012) as well. Their PCEs of devices matching different donors were predicted through machine learning (ML). In traditional device structures and crude environments, a maximum PCE is about seven times higher than original. Herein, a comprehensive investigation, ranging for conformations → donor/acceptor interfaces → morphology → PCEs, is carried out by pure theoretical methods. Therefore, this quantitative micro‐analysis combined with the ML intelligent prediction leads to a new approach in the development of the next generation of nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

Structure of (M+@C 50 N 5 H 5)Mʹ−(M = Li and Na; Mʹ = Li, Na, and K) with alkalides characteristics and large nonlinear optical response. [Display omitted] • In this work, a novel type of compound (M+@C 50 N 5 H 5)Mʹ−(M = Li and Na; Mʹ = Li, Na, and K) was designed. • Their alkalides' properties are confirmed by their FMO and NPA charges analysis. • The proposed alkalides exhibited considerable first hyperpolarizability up to 1.91 × 105 a.u. Based on open-cage fullerenes C 50 N 5 H 5 , a novel type of compounds (M+@C 50 N 5 H 5)Mʹ− (M = Li, Na; Mʹ = Li, Na and K) was designed and studied. Firstly, their alkalides' properties are confirmed by their FMO and NPA charges analysis. In particular, the proposed alkalides exhibited considerable first hyperpolarizability (β 0) up to 1.91 × 105 a.u., which indicated that they could be regarded as high-performance novel NLO molecules. These alkalides will pave the way for further exploration of electronic-stable, high-performance NLO materials. [ABSTRACT FROM AUTHOR]

Non-fullerene organic solar cells (OSCs) based on Y6 molecule have developed rapidly in recent years, and the power conversion efficiency (PCE) varies greatly when the OSC device constructed by Y6 and donor molecules with small structural difference. In this work, the influence of six donor-acceptor (D-A) polymer donors on Y6 -based OSCs were focused. The ground-state properties (planarity, frontier molecular orbital energy levels, driving force), excited-state properties of donors (primary indicators, Coulomb attraction) and donor/acceptor interfaces (Frenkel excitation (FE) and charge transfer (CT) states, electron coupling and charge separation rates) were discussed. The results show that symmetrical alkyl chains in the acceptor unit is favorable for maintaining planarity of molecule, while fluorination induces twisting in the thiophene bridge and acceptor unit. And the investigated high-performance molecules have desirable driving force, smaller Coulomb attraction and significant degree of holes and electrons delocalization. Also, the highest-performance system has multiple charge transfer pathways, which can improve charge separation efficiency. At the same time, high-performance systems often have better planarity and more favorable substituent positions. The high-performance donor/ Y6 systems have more advantage in charge separation than the low-performance systems. This work provides a fundamental understanding of the impact of D-A type donor materials on the cell performance and theoretical guidance for further optimization of polymer donor materials in Y6 -based OSCs. [Display omitted] • The relationship between the structure of donors and the performance of Y6 -based devices has been theoretically investigated. • High-performance donors have desirable driving force, small Coulomb attraction and significant hole-electron delocalization. • Polymer donors with improved planarity has multiple charge transfer pathway and fast charge separation rate. [ABSTRACT FROM AUTHOR]

A family of heterojunction photocatalysts C 60 /TpPa have been constructed from fullerenes (C 60) and TpPa-1 via in-situ solvothermal method firstly. The photocatalytic activity toward CO 2 of C 60 /TpPa has been evaluated through the gas-solid reaction system under pure CO 2 and low concentration CO 2 (10 %) atmosphere, respectively. The results show that the maximum CO formation rates for C 60 /TpPa are as high as 48.16 μmol·g−1·h−1 and 90.25 μmol·g−1·h−1 under pure CO 2 and 10 % CO 2 environment, respectively. The attractive experimental phenomenon is assigned to the existence of C O groups in TpPa-1. Due to the presence of Z-scheme heterojunction, the separation of photoexcited electrons and holes is effectively enhanced, and the photocatalytic performances are significantly improved. This work suggests that the construction of COF-based photocatalysts with heterojunction for efficient photoreduction of CO 2 is a promising strategy. [Display omitted] • It is the first work that combining C 60 with TpPa-1 build Z-scheme heterojunction photocatalysts. • Due to the presence of C O groups, C 60 /COF achieve higher performance in 10 % CO 2 environment. • Z-scheme heterojunction enhances the performances by improving the efficient separation of photo-excited electrons and holes. [ABSTRACT FROM AUTHOR]

Recently, the non-fullerene acceptor ITIC has attracted a lot of attention in terms of its prominent performance in organic solar cell (OSC). A better match with the donor materials is critical for it, so we on one hand compared the match of two typical donors PBDB-T and PBQ-0F with ITIC trying to find the main difference between them. On the other hand, we designed two donors 1 and 2 based on the same 2D-BDT unit and estimated their cell efficiency aiming to explore more effective donors for ITIC . The molecular dynamics simulation was carried out to get more practical photovoltaic interface, and the density functional theory was employed to estimate the cell efficiency. It is found that PBDB-T not only exhibits higher charge separation efficiency depending on larger charge separation and smaller charge recombination rates than PBQ-0F , but also displays stronger electron-hole coherence from donor to acceptor fragments at its S 1 state than PBQ-0F indicating its easier exciton dissociation at excited states. The stronger electron-withdrawing ability of the acceptor fragment in PBDB-T is concluded to make the main contribution to its higher charge separation efficiency, which is further proved by our designed donors 1 and 2 . Molecule 2 with stronger electron-withdrawing ability of the acceptor fragment than PBDB-T shows better charge separation performance at the interface than PBDB-T , which again suggests introducing strong electron-withdrawing group in this kind of donors may be a good choice for improving the performance of organic solar cell using ITIC as acceptor. [ABSTRACT FROM AUTHOR]