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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]

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 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]

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]

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]

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]