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Local density approximation (LDA), several popular general gradient approximation (GGA), hybrid module based density functional theoretical methods: SVWN, BLYP, PBE, HCTH, B3LYP, PBE1PBE, B1LYP, and BHandHLYP, and some nonstandard hybrid methods are applied in geometry prediction for C60 and C70. HCTH with 3-21G basis set is found to be one of the best methods for fullerene structural prediction. In the predictions of relative stability of C50 isomers, PM3 is an efficient method in the first step for sorting out the most stable isomers. HCTH with 3-21G predicts very good geometries for C50, similar to the performance of B3LYP/6-31G(d). The gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital from the predictions of all the density functional theory methods has the following descending order: Egap(half-and-half hybrid)>Egap(B3LYP)>Egap(HCTH)(GGA)>Egap(SVWN)(LDA). [ABSTRACT FROM AUTHOR]

A series of three-coordinate octupolar compounds with varied centers (boron, aluminum, and nitrogen), which exhibit very large effective two-photon absorption cross sections have been theoretically studied. The ground state geometries and electronic structures are obtained using the density functional theory with the B3LYP functional and 6-31G(d) basis set, and the results are comparable to the available experimental determinations. Based on the correct geometrical and electronic structures, the one- and two-photon absorptions are predicted by the ZINDO-SOS method. Among these compounds, the boron (B) and aluminum (Al) centers act as acceptors, while the nitrogen center acts as donor according to the net charge changes during the excitation. It is found that (i) the compounds with boron and aluminum centers show two large two-photon absorption peaks, while the molecule with nitrogen center show only one two-photon absorption peak; (ii) the cross sections of the molecules with B or Al as centers are larger than that of the molecule with nitrogen as center; furthermore, the two-photon absorption cross section of the molecule with Al center is larger than that of the molecule with B center, from this point of view, our theoretical prediction provides for the experiment a good new candidate with large two-photon absorption cross section for further research; (iii) lengthening the conjugation bridge by inserting a benzene ring on the organoborane compounds (forming the investigated molecule B-2) enhances the two-photon absorption cross section, and keeping good transparency at the same time. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A series of regiochemically varied and core size extension-modulated arene- and fluoroarene-thiophene co-oligomers and the unsubstituted sexithiophene α6T were investigated theoretically to explore their electronic and optical properties. These phenylene-thiophene oligomers show great potential for application in organic light-emitting diodes (OLEDs), organic diode lasers, and organic thin-film transistors (OTFTs) because of their feasible tuning of optical and electronic properties by the various structural tunings. Density functional theory (DFT) and the ab initio HF were employed to investigate the geometric and electronic structures of the oligomers in the ground state, and the singles configuration interaction (CIS) methods were used to study the lowest singlet excited state. The lowest excitation energies (Egs), the radiative lifetime τ, and the maximal absorption/emission wavelength of the oligomers were studied within time-dependent DFT (TDDFT). All calculations were performed using the 6-31G(d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials (IPs), electron affinities (EAs), and reorganization energies are significantly affected by the various structural tunings in these co-oligomers, which is important for the improvement of the hole and electron injection into OLEDs. Interestingly, the LUMO energy of 1b, 2b, and 3b is lower than that of α6T and 1a, 2a, 3a by about 0.12 ∼ 0.47 eV, indicating that the fluorophenyl-substitution has significantly improved the electron injection properties of the oligomers. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The purpose of this work is to provide an in-depth investigation of the electronic and optical properties of a series of n-type conjugated oligomers, including 4-phenyl-6-(4-phenylquinolin-6-yl)quinoline (B1), 6,6′-bis(2,4-diphenylquinoline) (B1PPQ), 6,6′-bis(2-(4-tert-butylphenyl)-4-phenylquinoline) (BtBPQ), 6,6′-bis(2-p-biphenyl)-4-phenylquinoline) (B2PPQ), and 4-(6-(2-(4-aminophenyl)-4-phenylquinolin-6-yl)-4-phenylquinolin-2-yl)benzenamine (BNPPQ). The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized with ab initio CIS. To assign the absorption and emission peaks observed in the experiment, we computed the energies of the lowest singlet excited states with time-dependent (TD) DFT (TD-DFT). All DFT calculations were performed using the B3LYP functional and the 6-31G basis set. The results show that the HOMOs, LUMOs, energies gaps, ionization potentials and electron affinities for each molecular are significantly affected by varying the aryl substituents, which favor the hole injection into OLEDs. The absorption and emission spectra exhibit red shifts to some extent [the absorption spectra: 335.85 (B1)< 370.63 (B1PPQ) < 376.77 (BtBPQ)< 388.67 (B2PPQ)< 412.93 nm (BNPPQ); the emission spectra: 391.48 (B1)< 430.11 (B1PPQ)< 435.86 (BtBPQ)< 444.57 (B2PPQ)< 463.28nm (BNPPQ)]. The radiative lifetimes (τ) of each oligomers are calculated as well. Because of introducing the cooperation with the electron donators such as the amidocyanogen in the common 4-phenyl-6-(4-phenylquinolin-6-yl)quinoline core for BNPPQ, which results in improving the hole-creating ability. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we have theoretically investigated bis((4-phenylethynyl)phenyl) ethynyl)bis(trimethylphosphine)platinum(ll) (PE2) and its analogs—three platinum acetylide complexes (1-3) that feature highly π-conjugated ligands (alkynyl-dimethylfluorene substituted with electron-donating or -withdrawing moieties). The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, P, N, S) basis set level by the density functional theory (DFT) method; one-photon absorption properties have been calculated by using time-dependent DFT (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods, and two-photon absorption (TPA) properties are obtained with the ZINDO/sum-over-states method. The values of βsp and βd for Pt are adjusted to -1 eV and -28.5 eV, respectively, to make one-photon absorption spectra calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate that all molecules in this work (involving cis isomers of molecules 1-3) take on two TPA peaks in the 600-800 nm region. The peak at 700-750 nm should not be simply attributed to the appearance of noncentrosymmetric cis isomers in solution, although trans and cis isomers adhere to a different selection rule. Every TPA peak results from its transition character. Molecules 1-3 show greater two- photon absorption strength compared with PE2 and retain good transparency. [ABSTRACT FROM AUTHOR]

Bis-dipolar emissive oligoarylfluorenes, OF(2)Ar-NPhs(2), bearing an electron affinitive core, 9,9-dibutylfluorene, as conjugated bridges and diphenylamino as endcaps, show great potential for application in organic light-emitting diodes. The various electron affinitive central aryl cores that include thiophene S,S‘-dioxide, dibenzothiophene S,S‘-dioxide, 2,1,3-benzothiadiazole, 4,7-dithien-2-yl-2,1,3-benzothiazole, dibenzothiophene, and dibenzofuran produce a remarkable influence on their optical and electronic properties. In this contribution, we apply quantum-chemical techniques to investigate a series of bis-dipolar diphenylamino-endcapped oligoaryfluorenes, OF(2)Ar-NPhs(2). The geometric and electronic structures in the ground state are studied using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states are optimized with ab initio CIS. The maximal absorption and emission wavelengths are investigated by employing time-dependent density functional theory (TDDFT). As a result, HOMOs, LUMOs, energy gaps, ionization potentials, electron affinities, and reorganization energies are affected by varying the electron affinitive cores in OF(2)Ar-NPhs(2). The absorption and emission spectra of this series of bis-dipolar oligoarylfluorenes also exhibit red shifts to some extent due to the electron-withdrawing property and the conjugated length of the electron affinitive cores. Remarkably, their calculated emission spectra can cover the full UV−vis spectrum (from 412 to 732 nm). Also, the Stokes shifes are unexpectedly large, ranging from 34 to 234 nm, resulting from a more planar conformation of the excited state between the two adjacent units in the oligoarylfluorenes. All the calculated results show that the oligoarylfluorenes can be used as hole and electron transport/injection materials in organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

The purpose of this work is to provide an in-depth interpretation of the optical and electronic properties of a series of phosphole derivatives, including 2,5-diphenylthiooxophosphole (2a), 2-phenyl-5-biphenylthiooxophosphole (3a), 2-phenyl-5-stilbenylthiooxophosphole (4a), 2,5-dithienylthiooxophosphole (2b), 2-thienyl-5-biphenylthiooxophosphole (3b), 2-thienyl-5-stilbenylthiooxophosphole (4b), and dibenzophosphole 1. These thiooxophospholes show great potential for application in OLEDs as efficient red emitters due to the tuning of the optical and electronic properties by the use of various substituents at the 2,5-positions of the phosphole ring. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized with ab initio CIS. To assign the absorption and emission peaks observed in the experiment, we computed the energies of the lowest singlet excited states with time-dependent DFT (TD-DFT). All DFT calculations were performed using the B3LYP functional and the 6-31G (d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials, and electron affinities for the phosphole derivatives are significantly affected by varying the phosphole ring substituents at the 2,5-positions, which favor the hole and electron injection into OLEDs. The absorption and emission spectra exhibit red shifts to some extent [the absorption spectra: 339.63 (1) < 358.65 (2a) < 373.77 (3a) < 443.89 nm (4a) and 403.03 (3b) < 449.11 (2b) < 460.19 nm (4b); the emission spectra: 418.42 (1) < 513.62 (2a) < 556.51 (3a) < 642.59 nm (4a) and 568.31 (2b) < 631.11 (3b) < 647.35 nm (4b)] and the Stokes shifts are unexpectedly large ranging from 78 to 228 nm resulting from a more planar conformation of the excited state for the phosphole derivatives. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

We present a detailed study of the structural, electronic, and optical properties of the bis-dipolar emissive oligoarylfluorenes, OF(2)Ar-NPhs. The aim of our quantum-chemical calculations is to investigate the role of the transition and the influence of the optical properties of the various central aryl cores in the oligoarylfluorenes. Geometry optimizations were performed for the ground-state and for the first electronically excited-state. The absorption and emission spectra were calculated using time-dependent density functional theory (TD-DFT). The results show that the HOMO, LUMO, energy gap, ionization potentials (IP), electron affinities (EA) and reorganization energy (λ) of the oligoarylfluorenes are significantly affected by the electronic withdrawing property and the conjugated length of the central aryl core. Consistently, the stronger the electron withdrawing strength, the lower the LUMO energy is. This thus improves the electron-accepting and transporting properties by the low LUMO energy levels. The absorption and emission spectra of this series of bis-dipolar molecules exhibit red shifts to some extent by the electronic nature of the electron affinitive central core in the oligoarylfluorenes. All the calculated results show that the oligoarylfluorenes are promising as useful light emitting materials for OLEDs. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The molecular equilibrium structures, electronic structures, and one- and two-photon absorption (TPA) properties of C2v(Zn(II), Fe(II) and Cu(I)) dipolar and D2d(Zn(II) and Cu(I)) and D3(Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands have been studied by the ZINDO-SOS method. The calculated results show that one- and two-photon absorption properties of metal complexes are strongly influenced by the nature of the ligands (donor end groups and linkers) and metal ions as well as by the symmetry of the complexes. The length of the -conjugated backbone, the Lewis acidity of the metal ions, and the increase of ligand-to-metal ratio result in a substantial enhancement of the TPA cross sections of metal complexes. Substitution of CN and NN for CC plays an important role in altering the maximum TPA wavelengths and the maximum TPA cross sections of metal complexes. Of them, the CN substituted metal complexes have relatively large TPA cross sections. Replacing styryl with thienylvinyl makes the one-photon absorption wavelength red shift and at the same time leads to a great decrease of the maximum TPA cross sections of metal complexes. The possible reason is discussed. In the range 500−1250 nm, octupolar metal complexes exhibit intense TPAs and therefore are promising candidates for TPA materials. [ABSTRACT FROM AUTHOR]

The ground and excited structures of the molecules are compared basis on the calculated by HF and CIS, respectively. The ionization potentials (IPs), electron affinities (EAs) and HOMO–LUMO gaps (ΔEHOMO–LUMO) of the oligomers are studied by the density functional theory (DFT) with B3LYP functional while the vertical excitation energies (Egs) and the maximal absorption wavelength λabs of oligomers of bifluorene and its derivatives DFE, DFA, DFBT, FDBO, and FSCHD are studied employing the time dependent density functional theory (TD-DFT) and ZINDO. Compared with BF, the derivatives DFE, DFA, and DFBT are better conjugated, easier to give an electron or a hole, as well as get an electron or a hole. Their HOMO–LUMO gaps are narrower and they have lower vertical excitation energies. The absorption and emission spectra of them are red shifting. However, FDBO and FSCHD are in the other way round. It is important that FDBO and FSCHD are good blue emitters. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G) and ZINDO/SOS methods. The electronic structure, one-photon absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths maxare blue-shifted and the TPA cross sections maxare increased 22.7-112.1 GM when the N atoms one by one are inverted from core to position to form multiply N-confused porphyrins. Especially maxof N3CP get to 164.7 GM. The electron donors -C6F5s at meso-position can make the TPA cross section maxincrease. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N3CP, N4CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation. [ABSTRACT FROM AUTHOR]

The electronic structures, one-photon absorption (OPA), and two-photon absorption (TPA) properties of a series of ferrocene-based chromophores with TCF-type acceptors (TCF 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran) have been studied by using the ZINDO-SOS method. The results have revealed that OPA and TPA of ferrocenyl derivatives are affected by the strength of the acceptor, especially the -bridge conjugation length. The TPA cross section increases with increasing acceptor strength and -bridge conjugation length. The TCF-type acceptor with a phenyl group can lead to a larger TPA cross section. Quadrupole molecules have the largest TPA cross sections (2000-3000 GM), which are about 4 times that of the corresponding dipolar molecules, indicating larger interactions between the top and bottom branches. Finally, the origins of the two-photon excitations for ferrocenyl derivatives are analyzed. The calculations show that ferrocenyl derivatives with TCF-type acceptors (especially quadrupole molecules) are promising candidates for TPA materials. [ABSTRACT FROM AUTHOR]

The electronic structures and the one- and two-photon absorption (TPA) properties of two series of the olefin-linked paracyclophane (pCp) oligomers have been studied using AM1 and ZINDO-SOS methods. The relationship between the TPA cross sections and the molecular chain length is obtained. The maximum TPA cross section increases in proportion to Nα (N denotes the number of repeat units) and the values of α depend on different molecular structures. The olefin-linked pCp oligomers, which have good transparency and large TPA cross sections, are promising candidates for TPA materials. [ABSTRACT FROM AUTHOR]

Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)-co-alt-2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (ΔH-L), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength λabs of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as ΔH-L, Eg, IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)n series. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 969–979, 2005 [ABSTRACT FROM AUTHOR]

The application of polyfluorenes in polymeric light-emitting diodes has been hampered because of the charge injection difficulties and the troublesome formation of a tailed emission band at long wavelengths (>500 nm) during device fabrication and operation, leading to both a color instability and reduced efficiency. The incorporation of the phenothiazine units has been proven to significantly enhance the hole injection and charge carrier balance and at the same time efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate poly[10-(N-(2′-methyl)phenothiazine-3,7-diyl) and its fluorene copolymer poly[10-(N-(2′-methyl)-phenothiasine-3,7-diyl)-co-alt-2,7-(9,9-dimethylfluorene)] (PFPTZ) and gain a detailed understanding the influence of phenothiazine units on the electronic and optical properties of fluorene derivatives. Density functional theory (DFT) and time-dependent DFT approaches are employed to study the neutral molecules, HOMO-LUMO gaps (ΔH-L), the lowest excitation energies (Eg's), positive and negative ions, as well as the IPs and EAs, focusing on the superiority of the electronic and optical properties attributed to the introduction of electron-donating moiety phenothiazine (PTZ) through comparing with pristine polyfluorene. The outcomes show that the highly nonplanar conformation of phenothiazine ring in the ground state preclude sufficiently close intermolecular interactions essential to forming aggregates or excimers. Furthermore, the HOMO energies lift about 0.4 eV, and thus, the IPs decrease about 0.3 eV in PFPTZ, suggesting the significant improved hole-accepting and transporting abilities, due to the electron-donating properties of phenothiazine ring by the presence of electron-rich sulfur and nitrogen heteroatoms and highly nonplanar characters, resulting in the enhanced performances in both efficiency and brightness compared with pristine polyfluorene. In addition, even though the introduction of electron-donating moiety PTZ onto fluorene leads to a slight bathochromic shift in absorption and emission spectra, the copolymer still exhibited strong blue emission. [ABSTRACT FROM AUTHOR]

The absorption and emission spectra for a series of substituted 1,3-diphenyl-5-pyrene-2-yl-4,5-dihydro-1H-pyrazole (DPPyP) molecules are computed by TDDFT methods. The solvent effect is modeled using the self-consistent reaction field (SCRF) method with Tomasi's polarized continuum model (PCM). The ground-state geometries were optimized by the Hartree–Fock method with the 6-31G basis set (and also with 3-21G* for molecule A) (HF/6-31G), and the lowest singlet excited-state geometries were optimized at the ab initio CIS level with the 6-31G basis set (CIS/6-31G). The calculated results indicate that the TDDFT method can reproduce the experimental values. We consider the effects of different basis sets on the optimization of the ground-state geometries. Specially, some insights on the differences observed for these compounds in changing the substituted donors (H, CH3, and NH2) and acceptor group (CN) are given; the results indicate that introduction of the donor groups will lead emission to be red-shifted, while introduction of the acceptor will induce the emission to be blue-shifted, which provides useful information for modulating light-emitting material colors. [ABSTRACT FROM AUTHOR]

Using density functional theory and the semiempirical ZINDO method, we have investigated the equilibrium geometries, electronic spectra, and the second and third hyperpolarizabilities of C74 and the metallofullerene Ca@C74. Theory predicts that Ca@C74 has greater stability than C74 and that the UV–Vis spectrum of Ca@C74 shifts to the blue. Both species possess relatively large βμ values and thus are promising as nonlinear optical materials. [Copyright &y& Elsevier]

The geometrical structure, electronic structure, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the perylene tetracarboxylic derivatives (PTCDs) were studied theoretically by using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods. The results revealed that increasing the number of naphthalene nucleus, extending the conjugated length on long axis, increasing the strength of donor group on lateral side, decreasing the ΔEH-L (energy gap between the highest occupied orbital and the lowest unoccupied orbital) and keeping the conjugation effect and inductive effect along the same molecular axis are the efficient ways to enlarge TPA cross section of PTCDs compounds. The results that PTCDs compounds exhibited extremely large TPA cross section of around 800–1100 nm (near infrared region) shed light into the significance of the PTCDs compounds for applications in TPA labeling materials in vivo. [ABSTRACT FROM AUTHOR]

All the 924 classical isomers of fullerene C56 have been investigated by PM3, and some most stable isomers are refined with HCTH/3-21G and B3LYP/6-31G(d) methods. D2:003 with the least number of adjacent pentagons is predicted to be the most stable isomer at B3LYP/6-31G(d) level, while Cs:022 and C2:049 possess nearly degenerate energies with relative energies of 0.03 and 3.90 kcal/mol, respectively. However, as to dianionic C562- fullerene, C2v:011 is predicted to be the most stable isomer. Investigations also show that the encapsulation of Ca atom in C56 fullerene is exothermic and the metallofullerenes Ca@C56 can be described as Ca2+@C562-. The computed relative stabilities show that the D2:003 behaves more thermodynamically stable than other isomers in a wide temperature interval, and C2v:011 should also be an important component. The electronic isomerization of C56 (C2v:011) and C50 (D5h:002) indicates that this phenomenon might be rather general in fullerenes and causes different properties, thus bringing about new possible applications of fullerenes. The static second-order hyperpolarizabilities of the three most stable isomers are slightly larger than that of C60. [ABSTRACT FROM AUTHOR]

The 437 classical isomers of fullerene C52 have been studied by PM3, HCTH/3-21G, and B3LYP/6-31G(d). C2:029 with the least number of adjacent pentagons is predicted to be the most stable isomer. The investigations show that both the number of adjacent pentagons and the degree of aromaticity play important roles in the relative stabilities of fullerene isomers. To clarify the relative stabilities of the C52 isomers in a wide range of temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. C2:029 prevails in a wide temperature range. In addition, the electronic spectra and second-order hyperpolarizabilities are determined by means of ZINDO and sum-over-states model. The static second-order hyperpolarizability of C2:029 is 51% larger than that of C60. Furthermore, intensity-dependent refractive index γ (-ω;ω,ω,-ω) (ω=1.1653 eV) of C2:029 is 13 times larger than that of C60. The encapsulation of Ca atom in C52 fullerene is exothermic and the metallofullerene Ca-C52 is described as Ca2+-C522-. [ABSTRACT FROM AUTHOR]

Among all the 4478 classical isomers of C66, C66( C s:0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66( C2 v:0011) and C66( C2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66( C2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66( C2 v:0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage. [ABSTRACT FROM AUTHOR]

Doubly ortho-linked cis-4,4′-bis(diarylamino)stilbene/fluorene hybrids have potential application in organic light emitting diodes. These organic molecules can function as efficient hole transport materials, with sky-blue emission and high efficiency and stability. To reveal the relationship between the properties and structures of these functional materials, we apply quantum-chemical techniques to investigate their optical properties and electronic structures. It is found that 8- and 8′-substituents give an antibonding contribution to the highest occupied molecular orbitals (HOMO), thus increasing the HOMO energy, implying an enhancement of hole-creating ability. Changes in ionization potentials confirm this presumption. The absorption and emission spectra exhibit red shifts to some extent with the various 8- and 8′-substituents, which are in good agreement with the experimental values. The Stoke shifts range moderately from 40 to 86 nm, due to the rigid spiral structure that hinders geometrical relaxation. [ABSTRACT FROM AUTHOR]

The 3465 classical isomers of C64 fullerene have been investigated by quantum chemical methods PM3, and the most stable isomers have been refined with HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-311G(d)//B3LYP/6-31G(d) level. C64(D2:0003) with the lowest e55 (e55 = 2), the number of pentagon-pentagon fusions, is predicted to be the most stable isomer and it is followed by the C64(Cs:0077) and C64(C2:0103) isomers within relative energy of 20.0 kcal/mol. C64(D2:0003) prevails in a wide temperature range according to energy analysis with entropy contribution at B3LYP/6-31G(d) level. The simulated IR spectra and electronic spectra help to identify different fullerene isomers. All the hexagons in the isomers with e55 = 2 display local aromaticity. The relative stabilities of C64 isomers change with charging in ionic states. Doping also affects the relative stabilities of fullerene isomers as demonstrated by Sc2@C64(D2:0003) and Sc2@C64(Cs:0077). The bonding of Sc atoms with C64 elongates the C&bond;C bond of two adjacent pentagons and enhances the local aromaticity of the fullerene cages. Charging, doping, and derativization can be utilized to isolate C64 isomers through differentiating the electronic and steric effects. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [ABSTRACT FROM AUTHOR]

The photophysics of a series of molecular organic light-emitting diodes (OLEDs) has been studied by theoretical calculation. These molecular OLEDs have been integrated by an electron- and hole-transporting components as well as an emitting components into the donor-π-acceptor (D-π-A) structures: 2-carbazolyl-7-dimesitylboryl-9,9-diethylfluorene (1), trans-4′-N-carbazolyl-4-dimesitylborylstilbene (2), and trans-2-[(4′-N-carbazolyl)styryl]-5-dimesitylborylthiophene (3). To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials and electron affinities were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The lowest excitation energies (Eg) and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory methods. The solvent effect on the emission spectra of these compounds was considered by a polarizable continuum model. As a result of these calculations, it was concluded that the electron injections of these compounds are much easier than Mes2B[p-4,4′-biphenyl-NPh(1-naphthyl)], and the diethylfluorene-based compound has higher electron mobility and better equilibrium properties as compared to the stilbene-based and styrylthiophene-based compounds. [ABSTRACT FROM AUTHOR]

The electronic structures and stabilities of pure M12-and M122-were systematically investigated within density functional theory. The nucleus-independent chemical shifts (NICSs) of IhSn122-and Pb122-are −5.0 and −20.7 ppm, respectively, based on B3LYP/aug-cc-pVDZ-PP predictions, whereas the NICS of Sn122-is predicted to be 1.1 ppm by B3LYP/LanL2DZ. A startling conclusion is that the NICS4dof Sn122-and NICS5dof Pb122-are −5.0 and −7.5 ppm, respectively, suggesting the significant contribution of the inner d orbitals to the total NICS values. This provides the first quantitative evidence for the existence of “d-orbital aromaticity” in Sn- and Pb-based clusters with three-dimensional structures. The d orbitals also contribute to the total NICSs of the K-coordinated clusters. The NICS predictions suggest that larger basis sets including d-orbitals are needed to analyze the aromaticity of some main-group-metal-based clusters (e.g., Sn- and Pb-based clusters) to obtain accurate predictions. [ABSTRACT FROM AUTHOR]

Calculations with B3LYP within quantum chemical density functional theory have been carried out for 1-H-phosphininium cation and a series of 1-R-phosphininium molecules (R = cyclopentadiene, α and β pyrroles, α and β phosphole, C5BH5&bond; and CH2&bond;). The negative nuclear-independent chemical shift values and the positive aromatic stabilization energies confirm that they are aromatic compounds. In particular, the 1-H-phosphininium cation even exhibits stronger aromatic character than the well-known aromatic phosphinine. The aromatic substituents have strong capability to attract electrons. It is the conjugation and aromaticity that keeps the stability and conformations of the molecules investigated. Owing to the perturbation of the aromatic substituted groups, the predicted large T values and the enlarged HOMO-LUMO gap of the phosphininium cation indicate that these compounds are expected in experiment. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

Stimulated by recent preparation and characterization of the first C58F18fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18(A) and C58X18(B), where X H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from −10.0 to −13.9 ppm) of C58X18(A) and C58X18(B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18(B), which has been experimentally characterized, C58F18(A) should also be isolated. In addition, C58F18and C58Cl18are predicted to possess large electron affinities, especially for C58F18(B) and C58Cl18(B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18and C58Cl18can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18greatly decrease compared to those of C58. [ABSTRACT FROM AUTHOR]

We report on a quantum-chemical study of the electronic and optical properties of gold(I) complex AuTFT (1) and its electron-withdrawing substitutents, AuTFOT (2) and AuTFCNT (3) where TFT diethynylfluorenyl, TFOT diethynylfluorenone and TFCNT diethynyl-(9-(dicyanomethylene)fluorene). Our theoretical calculations indicate that for all systems the reorganization energies of electron and hole are in the same order of magnitude and similar to those of the well-known electrontransport material Alq3. The substitution of -CO and -C(CN)2for -CH in AuTFT significantly decreases the bond length alternation and increases the electron affinity, which would effectively lower the energy barrier for electron injection from cathode and thus qualify AuTFOT (2) and AuTFCNT (3) as candidates for the electron transport layer (ETL) in light-emitting diodes (LEDs). The lowest lying excited-states of gold(I) diethynylfluorenyl derivatives have been studied by the singles configuration interaction (CIS) method and time-dependent density functional method (TDDFT). It is found that the electron-withdrawing substitutions evidently decrease the energy gap, leading to a remarkable red shift in transition energy and transformation in the direction of charge transfer. Our research is important in the development of new functional materials for the design of LEDs with enhanced performance. [ABSTRACT FROM AUTHOR]

Poly(fiuorene)-type materials are widely used in polymer-based emitting devices. One of the drawbacks of light-emitting diodes based on polyfiuorene derivatives is the injection of holes from the anode due to the high ionization potential (IP) of most derivatives. Substitution by electrondonating alkoxy substituents or by adding charge carriers on the conjugated polymer's backbone produces a remarkable influence on its electrical and optical properties. In this contribution, we apply quantum-chemical techniques to investigate a family of π-conjugated polymers with substituted dimethoxy groups at the 3,6 positions of the fiuorene ring, namely, poly(2,7-(3,6dimethoxy-fiuorene)(PDMOF), poly(2,7-(3,6-dimethoxy-fiuorene)-co-alt-fiuorene (PDMOFF), and poly(2,7-(3,6-dimeth-oxy-fiuorene)-co-alt-2,5-thiophene (PDMOFT). The electronic properties of the neutral molecules, HOMO-LUMO gaps (ΔH-L), in addition to the positive and negative ions, are studied using the B3LYP functional. The lowest excitation energies (Eg) and the maximal absorption wavelength Λabs of PDMOF, PDMOFF, and PDMOFT are studied by employing time-dependent density functional theory (TD-DFT) and the ZINDO semiempirical method. The IP, EA, and Eg values of each polymer were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The influence of the presence of methoxy groups on the fiuorene moiety on the ionization potential is especially emphasized. The outcomes show that the HOMO energies of these systems under study increase by about 0.4 eV and the IP values decrease by about 0.3 eV compared to those of the corresponding polyfiuorene. Both effects result in a reduction of the energy barrier for the injection of holes in related polymeric light-emitting devices and should contribute to the enhancement of their performances. Because of the cooperation with thiophene in PDMOFT, which results in a good planar conformation, both the hole-creating and electronaccepting abilities are improved. [ABSTRACT FROM AUTHOR]

The photophysical properties, which vary as X is varied, of Re(I)-halide complexes (X2-bpy)ReICl(CO)3 (where X = ph, DAE, DNE, and DPE; ph = phenyl (1); DAE = di(amineoethynylbenzene) (2); DPE = di(phenylethynylbenzene) (3); DNE = di(nitroethynylbenzene) (4); bpy=2,2'bipyridine), are investigated using density functional theory (DFT). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using B3LYP functional. Excited singlet and triplet states are examined using time-dependent density functional theory (TDDFT). The Iow-lying excited-state geometries are optimized at the ab initio configuration interaction singlets level. As shown, the diarylethynyl-based structure is an integral component of the bpy π-conjugated network, which results in a good planar structure. The occupied orbitals involved in the transitions have a significant mixture of metal Re and group Cl, and the lowest unoccupied orbital is a π* orbital, which extends from ligand bpy to diarylethynyl-based substituents. The luminescence for each complex originates from the lowest triplet excited states and is assigned to the mixing of MLCT and LLCT characters. Significant insights on the effects of these diarylethynyl conjugated structure and ending substituents (NH2, ph, and NO2) on absorption and emission spectra are observed by analysis of the results of the TDDFT method. The diarylethynyl-based π-conjugated network makes both the absorption and emission spectra red-shifted compared with simple complex (bpy)ReICl(CO)3. Furthermore, an electron-releasing group (NH2) makes absorption and emission spectra blue-shift and an electron-withdrawing group (NO2) makes them red-shift. [ABSTRACT FROM AUTHOR]

The one-photon and two-photon absorption properties of donor–acceptor substituted dehydrobenzo[18]annulenes were determined by using density functional theory and ZINDO methods. The macrocycle containing C2v symmetry exhibited the largest TPA cross-section value of 3376 × 10–50 cm4 s/photon. The calculated results indicate that the TPA response in the whole molecule comes from the contribution of that in the every side in the trigon. It is notable that the magnitudes of the transition dipole moment from the virtual intermediate state to the TPA final state and the dipole moment difference between the ground state and the virtual intermediate state play important roles in increasing the TPA cross-section value. This series of molecules can circumvent the trade-off between efficiency and transparency, and they provide a promising direction for the further development of novel two-dimensional molecules with such properties. [ABSTRACT FROM AUTHOR]

The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pcs) were studied using the semiempirical ZINDO method and time-dependent density functional theory (TDDFT), respectively. The compared results confirmed that the semiempirical ZINDO method was reasonably reliable when calculating the OPA of tetrabenzoporphyrins and phthalocyanines. On the basis of the OPA properties obtained from the ZINDO method, two-photon absorption (TPA) properties of two series of molecules were investigated, using ZINDO and sum-over-states (SOS) methods. The results showed that the TPA cross-sections of all molecules were in the range of 220.6 × 10–50 – 345.9 × 10–50 cm4·s·photon–1, which were in the same order of magnitude as the values reported in the literature. The relatively larger δ(ω) value for Pcs with respect to that for corresponding TBPs originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment between S0 and S1 and the transition dipole moment between S1 and S5. [ABSTRACT FROM AUTHOR]

Two-photonfluorescence probes used in two-photon fluorescencemicroscopy (TPM) can achieve intact tissue imaging without destruction.Therefore, for a long time, TPM has been an important tool in biologyand medicine. In this background via a quantum chemical method, aseries of zinc ion probe molecules using N,N-di(2-picolyl)ethylenediamine (DPEN) as the recognitiongroup were studied, which are based on the photoinduced electron transfer(PET) mechanism. The fact that the one-photon absorption peak is almostunchanged and the fluorescence emission intensity increased significantlyupon coordination with a zinc ion reveals that these probes can bePET fluorescent bioimaging reagents. And it is predicted that whenthe chemically modified probe molecule is incorporated with Zn2+, the two-photon absorption (TPA) cross-section (δmax) will greatly increase and the TPA peak will be in thenear-infrared region. The molecules after changing the fluorophorebecome more suitable for probing Zn2+in vivo, and a modificationat the end of the fluorophore can fine-tune the fluorescence and TPAproperties. The detailed investigations will provide a theoreticalbasis for synthesizing new zinc-ion-responsive two-photon fluorescentprobes. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons (GNRs) have attracted increasing attention due to high potentiality in nanoelectronics. In the present study, quantum-chemical calculations of structural and nonlinear optical properties have been first carried out for the nanoelectronical materials, a new series of ladder-type N-annulated quaterrylenes and their imide chromophores. The effects of the solvent, terminal groups, the number of N-annulated bridges, and π-conjugated length are discussed in detail. The solvent effect is significant on the one-photon absorption (OPA). Moreover, the OPA and two-photon absorption (TPA) properties of the two series of DI and N-MI molecules show a dear solvent dependence, which is attributed to the carboximide substitution featuring larger polarization. Introducing electron-donating groups and dicarboximides and increasing the conjugated length lead to red-shifts of the OPA, emission, and TPA spectra, lower emission lifetimes, and enhanced TPA cross sections (δmax), but further extension of the conjugated framework does not always promote an increase of δmax. The changing trends of δmax can be explained by the transition moment and the intramolecular charge transfer. All N-annulated quaterrylene and their imide derivatives possess small energy gaps, intense near-infrared absorption and emission, and large δmax, which are important for use as two-photon fluorescent labeling materials. [ABSTRACT FROM AUTHOR]

Two important classes of organic molecules, perylene diimide (PDI) and pyrene derivatives have been found to possess relatively excellent photophysical and photochemical properties and especially high two-photon absorption cross sections ( δ). Herein, one-photon absorption (OPA) and two-photon absorption (TPA) properties of some novel PDI and pyrene derivatives were comparatively investigated by the density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The calculated results indicate that with respect to PDI derivatives, the maximum TPA cross-sections for pyrene compounds increase obviously, the maximum peaks of OPA and TPA spectra are blue-shifted, the Δ E (energy gaps between the highest occupied orbital and the lowest unoccupied orbital) increase. The different π-conjugated bridges (fluorene and pyrene) and terminal groups have slight effect on the OPA properties. Nevertheless, the molecules bearing 1,6-disubstituted pyrene as the π-conjugated bridge display the largest δ in both series of compounds 3 and 4. Moreover, the δ values of molecules with benzothiazole-substituted terminal groups are larger than those of the molecules with diphenylamine, which is attributed to benzothiazole groups stabilizing the planarity of the branch parts, extending the conjugated length and increasing the π-electron delocalized extent. Furthermore, the molecular size has marked effect on OPA and TPA properties. It is worthy to mention that cruciform 8 displays the largest δ among all the studied molecules in the range of 600-1100 nm. This research could provide a better understanding for the origin of the linear and nonlinear optical properties, and it would be helpful to gain more information about designing two-photon absorption materials with large δ. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The photophysical properties of a series of multifunctional compounds applied in organic light-emitting diode (OLED) materials have been studied by quantum chemistry. These compounds have been integrated by an electron and hole transporting component as well as an emitting component into the donor–π–acceptor (D–π–A) structures. To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials and electron affinities were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The maximum absorption and emission wavelengths of compounds 1– 4 were calculated by time-dependent density functional theory method. As a result of these calculations, it was concluded that the electron injections of compounds 2– 6 are much easier than Mes2B[ p-4,4′-biphenyl-NPh(1-naphthyl)] (BNPB) due to the introduction of the thiophene group, anthracene group, and N=N as a part of the π-conjugated bridge, compounds 5 and 6 can act as electron transport and hole transport materials, respectively. Compounds 1 and 2 have higher electron mobility and light-emitting efficiency as compared to compounds 3 and 4. Compounds 3 and 4 have quite longer fluorescence lifetimes than compounds 1 and 2 due to the larger Stoke’s shifts. [ABSTRACT FROM AUTHOR]

The electronic structures, charge injection and transport, absorption and emission spectra, properties of two series of fluorene-based oligomers {2-[2-{2-[5-(9H-Fluoren-3-yl)-thiophen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran- 4-ylidene]-malononitrile} n (FTPM) n and {2-{2-{2-[5-(9H-Fluoren-2-yl)-2-hydroxy- 3-methoxy-phenyl]-vinyl}-6-[2-(2-hydroxy-3-methoxy-phenyl)-vinyl]-pyran-4- ylidene}-malononitrile} n (FOOPM) n ( n = 1–4) have been investigated by the density functional theory (DFT) approach. The ground-state geometries of (FTPM)4 and (FOOPM)4 optimized at B3LYP/6-31G(d) level exhibited zigzag arrangements. The energies of HOMO and LUMO, HOMO–LUMO energy gaps (Δ E H– L) of (FTPM) n and (FOOPM) n ( n = ∞) were obtained by linear extrapolation method. Moreover, the calculations of ionization potential (IP), electronic affinity (EA), and reorganization energy (λ) were used to evaluate the charge injection and transport abilities. For (FTPM)4 and (FOOPM)4, the TDDFT calculations revealed that the absorption peaks can be characterized as π–π* transition and couple with the location of electron density distribution changes in different repeat units. All the earlier theoretical investigations are intended to establish the structure–property relationships, which can provide guidance to design the organic light-emitting diodes (OLEDs) with high performance. [ABSTRACT FROM AUTHOR]

Ambipolar diphenylamino end-capped oligofluorenylthiophenes and fluoroarene-thiophene show great potential for application in organic light-emitting diodes (OLEDs). Here, we provide an in-depth investigation on the optical and electronic properties of OF(2)TP-NPh ( 1a), OF(2)DTP-NPh ( 2a), OF(2)TTP-NPh ( 3a), OF(2)QTP-NPh ( 4a), and 2,5-bis-(2,3,5,6-tetrafluoro-4-trifluoromethyl-phenyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene ( 5a). The geometric and electronic structures of the oligomers in the ground-state are studied with density functional theory (DFT) and ab initio Hartree-Fock, whereas the lowest singlet excited states are optimized by ab initio CIS. The energies of the lowest singlet excited states are calculated by employing time-dependent density functional theory (TDDFT). The results show that the highest occupied molecular orbitals, lowest unoccupied molecular orbitals, energy gaps, ionization potentials, and electron affinities for the oligomers are affected by the thiophene chain length and the different end-caps. The absorption and emission spectra exhibit red shifts to some extent due to the increasing thiophene chain length and the enhancing electron-donating property of the end-caps. Furthermore, the large Stokes shifts ranging from 58 to 80 nm are examined, resulting from a more planar conformation of the excited-state between the two adjacent units in the oligomers. All the calculated data show that the fluoroarene-thiophene has improved electron transport rate and charge transfer balance performance, and all the studied molecules can be used as ambipolar-transporting materials in OLEDs. [ABSTRACT FROM AUTHOR]

The first singlet excited state geometries of various isomers and tautomers of firefly oxyluciferin (OxyLH 2), as well as their fluorescence spectra in aqueous solution, were studied using time dependent density functional theory (TDDFT). With changing pH in aqueous solution, three fluorescence peaks, blue (450 nm), yellow-green (560 nm), and red (620 nm) correspond to neutral keto and enolic forms, the monoanionic enolic form, and the monocationic keto form respectively. A counterion, Na +, was predicted to cause a blue shift in the fluorescence of anionic OxyLH 2. The contributions of a charge transfer (CT) state upon electronic excitation of the planar and twisted structures were predicted. CT was large for the twisted structures but small for the planar ones. The differences between p Kand p K* of various oxyluciferin species were predicted using a Forster cycle. A new possible light emitter, namely, the monocation keto form (keto+1), was considered. [ABSTRACT FROM AUTHOR]

The 2385 classical isomers and four nonclassical isomers of fullerene C62have been studied by PM3, HCTH/3-21G//SVWN/STO-3G, B3LYP/6-31G(d)//HCTH/3-21G, and B3LYP/6-31G(d)//B3LYP/6-31G(d). The Cs:7mbrisomer, with a chain of four adjacent pentagons surrounding a heptagon, is predicted to be the most stable isomer, followed by C2v:4mbrwhich is 3.15 kcal/mol higher in energy. C2:0032 with three pairs of adjacent pentagons is the most stable isomer in the classical framework. To clarify the relative stabilities of C62isomers at high temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. Analyses reveal that Cs:7mbrprevails in a wide temperature range. The vibrational frequencies of the five most stable C62fullerene isomers are also predicted at the B3LYP/6-31G(d) level, and the simulated IR spectra show important differences in positions and intensities of the vibrational modes for different isomers. The nucleus-independent chemical shift and the density of states of the three most stable isomers show that the square in C2v:4mbrand the adjacent pentagons in Cs:7mbrand C2:0032 possess high chemical reactivity. In addition, the electronic spectra and second-order hyperpolarizabilities are determined by means of ZINDO and the sum-over-states mode. The intensity-dependent refractive index (−; , , −) at 2.3305 eV of Cs:7mbris very large because of resonance with the external field. The second-order hyperpolarizabilities of the five most stable isomers of C62are predicted to be larger than those of C60. [ABSTRACT FROM AUTHOR]