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Organic semiconductors are attractive candidates for the development of flexible and efficient optoelectronic devices. In this work, we have studied the pyrene end-capped thiophene derivatives with different number of oligomeric rings and substituted with their oxygen analogue furan. Results indicate that the molecular planarity varies with the substitution of furan rings and the number of rings play a role on optoelectronic property of the systems. All the systems have shown ambipolar behavior, but the high charge barrier in the case of electrons could limit the device performance. Further, in photovoltaic analysis the increment in oligomeric ring has substantially reduces the open circuit voltage and the fill factor. However, the introduction of furan has improved the overall light harvesting efficiency. With the proper choice of material and device engineering the shorter systems can be considered for photovoltaics, where as the longer derivatives can be considered for light emitting device applications. [Display omitted] • Pyrene end-capped oligothiophenes were substituted with oligofurans and investigated for optoelectronic applications. • Planarity analysis indicate furan substituted molecules are more planar than that of the thiophene systems. • The planarity varies with respect to the number of thiophene/furan rings. • Both oligothiophenes and oligofurans shows ambipolar behavior but furan substitution tends to favor the hole transfer. • Results indicate shorter systems are suitable for photovoltaics and longer systems are preferable for light emitting device applications. [ABSTRACT FROM AUTHOR]

Introduction Previous studies have demonstrated the potential of solvatochromic dyes for investigating the physical chemistry of homeopathic potencies. Results Following examination of this class of dyes in organic solvents, results obtained using the positively solvatochromic dye Bis-dimethylaminofuchsone (BDF) in aqueous solution are now reported. Spectral changes observed with this dye in the presence of potencies are both substantial and reproducible. Studies across a wide range of pH values reveal an unusual pH dependence for the dye's interaction with homeopathic potencies. Results indicate potency enhances dye protonation at pH values below c. 7.0, whilst protecting the dye from attack by hydroxyl ions above c. pH 7.5. Conclusion A possible explanation for these observations is offered in terms of a potency – induced electron density shift in BDF. The interaction of homeopathic potencies with solvatochromic dyes, particularly BDF, points towards a possible physico-chemical model for the nature of potencies, how they may be interacting with this class of dyes, and moreover how their biological effects may be mediated. [ABSTRACT FROM AUTHOR]

In this paper, the influence of different ancillary ligands on geometric structures, frontier molecular orbitals character, gap energy and electronic absorption spectra of [Ir(5-NO 2 -ppy) 2 (PPh 3 )(L)] (L = Cl − , NCO − , NCS − and N − 3 ) has been theoretically studied by density functional theory and time-dependent density functional theory calculations with B3LYP and PBE0 hybrid functionals. Calculated geometric parameters of studied complexes are in good agreement with the available experimental values. The theoretical absorption spectra reproduce the main properties of the experimental spectra. Both energy gaps and absorption spectra depend on the composition of HOMO Orbital, π-donor orbitals reduce the energy gaps and red shift the absorption spectra while π-acceptor orbitals increase the energy gaps and blue shift the absorption spectra. All the spectra are characterized by mixed MLCT/LLCT states in the visible energy domain. [ABSTRACT FROM AUTHOR]

Carrier heating (CH) theory in a four-wave mixing quantum dot structure has been investigated. The impact of wetting layer (WL) carrier density, CH time constant, effective intraband relaxation time have been examined. The derived heat capacity for QD structure have ( T - 1 ) dependence. It is shown here that both WL carrier density and QD excited state (ES) occupation controls the overall nonlinear contributions. Then inclusion of WL and ES in the CH induces a new equilibrium reached at a faster recovery time. The proposed model yields results in a line with experiments at high carrier density reflecting the efficiency of our model. [ABSTRACT FROM AUTHOR]

• The molecular properties of an insulating gas material under electric field were studied theoretically. • In the specific electric field direction, the molecular ionization potential decreases significantly. • The long carbon chain molecules may reduce the insulating performance of the insulating gas. With the deterioration of global greenhouse effect, CF 3 SO 2 F (Trifluoromethanesulphonyl Fluoride) has become an alternative gas of SF 6 (Sulfur Hexafluoride). CF 3 SO 2 F has environmentally friendly characteristics and has been widely concerned. In this work, we analyze the electric field level of the discharge in the dielectric and the direction of the molecular intrinsic dipole moment. Density functional theory and time-dependent density functional theory are used to calculate the molecular structure parameters, dipole moments, frontier orbitals and excited states at corresponding electric field levels and in specific electric field directions. C 2 F 5 SO 2 F and C 3 F 7 SO 2 F, as by-products in the synthesis of CF 3 SO 2 F, are studied together to explore the influence of carbon atom number on molecular properties. As a result, the molecular structure is clearly changed under the electric field and the molecular bond length strongly depended on the electric field. The HOMO is mainly contributed by O atoms and the LUMO is mainly contributed by S atoms. When the electric field in the -z-axis direction is applied, the HOMO energies of molecules increase, especially for C 3 F 7 SO 2 F molecule, and the ionization potentials decrease correspondingly. The reduced ionization potentials facilitate the liberation of electrons from the molecule and the propagation of the streamer. The excitation energy of each molecule in each excited state decreases with the increasing of electric field intensity. Therefore, during the preparation process of CF 3 SO 2 F molecule, C 3 F 7 SO 2 F molecule should be reduced or removed as much as possible to prevent the reduction of dielectric insulation strength. The finding of this study is beneficial to the performance improvement and application research of CF 3 SO 2 F. [ABSTRACT FROM AUTHOR]

The effect of external electric field on the ground and few singlet excited states of phenyalanine are studied in the light of TDDFT (time dependent density functional theory) and DFRT (density functional reactivity theory). The excited state geometries are compared with the ground state ones. Sensitivity of the reactivity parameters such as total electronic energy, energy of the HOMO (highest occupied molecular orbital), global hardness ( η ), electrophilicity ( ω ) etc. towards the external electric fields are measured by varying the applied field strength. Variation of aromaticity of the ground and excited states are gauged in terms of nucleus independent chemical shift (NICS). Geometry, reactivity and aromaticity of the ground as well as excited states are responsive to the presence of external electric field. [ABSTRACT FROM AUTHOR]

Dynamic electron correlation is very important for the correct description of potential energy surfaces, especially surface with differential dynamic electron correlation. Moreover, an accurate description of both the ground and excited state potential energy surfaces is essential to understand thermal and photochemical reactions of molecular systems. In the present work we test the performance of the Spectroscopy ORiented Configuration Interaction (SORCI) method that was originally designed to account for the dynamic electron correlation in an efficient manner at fixed geometry. Here, we assess the performance of SORCI along several paths on the ground and excited state potential energy surfaces that are related to the thermal and photochemical isomerization of a reduced retinal chromophore model. The ground state mapping involves three paths. Two of them are minimum energy paths that lead through different transitions states from one cis/trans stereoisomer to the other. One transition state has a diradical (open-shell) character while the other one has a charge-transfer character. The third ground state path connects these two transition states via a conical intersection. In addition, we assess the performance of SORCI for three excited state paths that comprise a minimum energy path starting from each of the cis and from the trans chromophore. These two pathways arrive at different conical intersections that are part of one seam of conical intersections. The third excited state path presents a profile along this seam. Despite the high complexity and varying mixture of different electronic structures involved in this benchmark, SORCI produces energy differences and energy profiles in good agreement with the multireference configuration interaction plus quadruples correction (MRCISD+Q) reference along all six paths. We find that SORCI is capable of producing smooth energy profiles, which require tighter thresholds than the present default. A further tightening of these thresholds by one order of magnitude yields converged SORCI values as compared to the limit of the method obtained by setting the three cutoffs to zero. However, we note also some deficiencies relative to MRCISD+Q in the description of relative energy differences. When comparing energies of structures that have very different geometries on the same potential energy surface we find that SORCI underestimates the reference values. Here SORCI underestimates the corresponding MRCISD+Q reference values thus indicating a non-negligible effect of the inactive double excitations. In addition we observe some artifacts at conical intersections due to the Davidson correction for higher excitations. Ways to overcome these drawbacks are discussed. [ABSTRACT FROM AUTHOR]

A systematic approach is introduced for defining Restricted Active Space Self-Consistent-Field (RASSCF) orbitals for treating multiple electronic states in a balanced way, based on an SCF state-averaging procedure (Thom and Head-Gordon, 2008). We start from an SCF density matrix averaged over the electronic states of interest and choose a RAS partition based on the corresponding natural orbital occupation numbers. In order to test this procedure, we apply it to naphthalene cation, previously studied as a potential interstellar Polycyclic Aromatic Hydrocarbon (PAH) because of its photo stability following electronic excitation (Hall et al., 2006). The results obtained with this method in terms of energies and bond lengths for the first three electronic states and the corresponding minimum energy conical intersections between potential energy surfaces compare very well with CASSCF results and suggest further testing of the method for RASSCF calculations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Excited properties of a covalent organic framework are studied. [•] Calculated spectra compare well with experiment result. [•] Adjacent layers are more stable if layers are horizontally offset. [•] Eclipsed AA stacking structure promotes the carrier mobility. [•] Low-symmetry offset structure is more conducive to luminescence. [ABSTRACT FROM AUTHOR]

Abstract: We developed the direct SAC-CI (symmetry-adapted cluster-configuration interaction) method for accurate calculations of electronic excited states of large molecules. The direct SAC-CI method uses an efficient MO (molecular orbital) direct scheme that is compatible with the perturbation-selection technique with using sparse linear algebra techniques. The direct SAC-CI can calculate large molecules with moderate computational cost. Using the direct SAC-CI method, excited states of free-base tetraazaporphyrin, phthalocyanine, naphthalocyanine, and anthracocyanine were studied. An interesting feature of the observed spectra is that the splitting of the Q-bands decreases with increasing molecular size. The SAC-CI calculation well reproduced the observed trend of excitation energies and showed the importance of electron correlation effects in the excited states. [Copyright &y& Elsevier]

Abstract: The properties of the ground and low-lying electronic excited states of OClO, OClO+ and OClO− are studied employing symmetry-adapted-cluster (SAC)/symmetry-adapted-cluster configuration interaction (SAC-CI) method. The geometry of the ground state of OClO is optimized by SAC method using different basis sets and the reasonable geometry of the ground state of OClO is obtained by SAC/6-311++G (2d, 2p) level. The properties of nine low-lying electronic excited states of OClO, such as geometries, vertical excitation energies, adiabatic excitation energies, transition dipole moments and oscillation strengths, are studied at SAC-CI method. By SAC-CI/6-311++G (2d,2p) level, the geometries of ten electronic states of OClO+ are optimized and the adiabatic ionization potentials (AIP) and the vertical ionization potentials (VIP) of OClO+ are calculated. The geometries of six electronic states of OClO− are optimized and the vertical detachment energies (VDE) and adiabatic detachment energies (ADE) of OClO− are obtained. Comparing with the available experimental and previous theoretical data, the SAC/SAC-CI/6-311++G (2d,2p) results are reliable. [ABSTRACT FROM AUTHOR]

Abstract: Ultrafast excited state dynamics of carotenoids in solution and bound to pigment-protein complexes have been investigated by means of femtosecond pump-probe spectroscopic measurements. Ultrafast triplet formation of carotenoids bound to pigmentprotein complexes was observed upon excitation of both carotenoids and bacteriochlorophyll. The anomalous reaction of triplet formation of carotenoids bound to pigment-protein complexes is discussed in terms of ultrafast triplet-triplet excitation energy transfer between carotenoid and bacteriochlorophyll. [Copyright &y& Elsevier]

Abstract: The low-lying electronic states of the CCCF radical and its ionic states have been investigated systematically using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with aug-cc-pVTZ basis set. To investigated the Renner–Teller effect on the CCCF radical, Cs symmetry was used for CCCF. The CCCF has been found to have a X2A′ ground state with rotational constant =4500.5MHz, which is in good agreement with the experimental values of 4555.8043MHz. The calculations of vertical excitation energies of CCCF at 2.893 and 4.180eV are attribute to the X2A′→32A″ and X2A′→52A′, respectively, which has larger oscillator strengths. The ionization potentials of CCCF are computed in order to provide a theoretical guidance to the photoelectron spectrum (PES) of the CCCF radical. The first adiabatic electron affinity (AEA) of CCCF is predicted to be 2.671eV. A comparison of the geometries and bonding among the CCCX (X=F, Cl, and Br) radicals presents the ground state X2A′ of CCCX can be described as allenic structures with the unpaired electron on the C3 atom, while the excited state 12A″ (12Π) of CCCX have the linear acetylenic structures with the unpaired electron on the C1 atom. The barriers to linearity decrease as follows: ΔE (CCCF)<ΔE (CCCCl)<ΔE (CCCBr). [ABSTRACT FROM AUTHOR]

Abstract: The time-dependent density functional theory (TDDFT) method was performed to investigate the hydrogen-bonding dynamics of methyl cyanide (MeCN) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground-state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated MeCN and MeOH monomers, the hydrogen-bonded MeCN–MeOH dimer and MeCN–2MeOH trimer are calculated by the DFT and TDDFT methods, respectively. According to Zhao’s rule on the excited-state hydrogen bonding dynamics, the intermolecular hydrogen bonds CHengthened in electronically excited states of the hydrogen-bonded MeCN–MeOH dimer and MeCN–2MeOH trimer in that the excitation energy of the related excited states are lowered and electronic spectral redshifts are induced. Furthermore, the hydrogen bond strengthening in the electronically excited state plays an important role on the photochemistry of MeCN in solutions. [ABSTRACT FROM AUTHOR]

Abstract: The ground and excited state behaviors of a biologically important mitochondria selective dye, 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-benzimidazolo carbocyanine (TTBC), were investigated in order to give useful information related to the enhancement of its electronic and optical properties. DFT and TDDFT levels of theory with different functionals and basis sets were used. The results obtained by using PBEPBE/6-31+G(d,p)/C-PCM are in good agreement with the experiments. The potential energy surface sections of TTBC were explored and the geometry optimized in the first excited state, S1, to analyze the fluorescence spectrum of the dye. There are two distinct minima on the S1 surface, one located near the ground state geometry and an energetically favorable twisted geometry, having a charge transfer character. The observation of similar ground and excited state dipoles as well as solvent-independent fluorescence and absorption wavelengths reveals that there is no competition between the two minima; the emission is dominantly coming from the more planar configuration. [ABSTRACT FROM AUTHOR]

• (TD)-DFT study of a series of benzo[ cd ]indole-based polymethine dyes. • Comparison of the ground and fluorescence state properties. • Fast deexcitation explained by the strong vibronic interactions in the S 1 state. • Localization of the frontier MOs on the chain and end-group in polymethine dyes. The electronic structure of a series of benzo[ cd ]indole-based merocyanines and cationic polymethine dyes has been analyzed in both the ground and fluorescent states using the DFT and TD-DFT computations. The obtained data has shown the marked difference between the benzo[ cd ]indole dyes and those based on such typical heterocyclic cores as indole and benzimidazole. Namely, in the former, the frontier MOs have much greater coefficients at the end group(s), which leads to an enhancement of vibronic interactions in the long-wavelength absorption and fluorescence transitions. This effect seems to be the major cause of the low fluorescence lifetimes and fluorescence quantum yields of benzo[ cd ]indole dyes. [ABSTRACT FROM AUTHOR]