The electronic spectrum of biphenyl

McLaughlin, T. G.; Clark, Leigh B.

doi:10.1016/0301-0104(78)87021-9

Cited by 36 publications

(14 citation statements)

References 21 publications

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“…A state of definite Ĉ2 symmetry may then be constructed as follows: [25] and crystalline films (b) [26], (c) [27], (d) [3], (e) [4]. (7), of the essential states for a 15 site oligomer.…”

Section: A Particle-hole Symmetry In the Molecular Orbital Basismentioning

confidence: 99%

Density matrix renormalization group calculations of the low-lying excitations and non-linear optical properties of poly(para-phenylene)

Barford

Bursill

Lavrentiev

1998

J. Phys.: Condens. Matter

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The two state molecular orbital (2-MO) model of the phenyl based semiconductors is used to calculate the low-lying spectra of the A + g and B − 1u states of poly(para-phenylene) (PPP). The model parameters are determined by fitting its predictions to exact Pariser-Parr-Pople model calculations of benzene and biphenyl, and it is solved using the density matrix renormalisation group method. It is shown that there exists a band of 1 B − 1u ('s'-wave) excitons below the band states. In the long chain limit the lowest exciton is situated 3.3 eV above the ground state, consistent with experimental data. The calculated particle-hole separation of these excitons indicates that they are tightly bound, extending over only a few repeat units. The lowest band PACS numbers: 42.70Jk, 71.20Rv, 78.66Qn, 71.35Cc Since the first light-emitting device based on poly(para-phenylenevinylene) (PPV) was reported [1], the non-linear optical (NLO) properties of conjugated polymers have been extensively investigated. Amongst the numerous systems studied, poly(para-phenylene) (PPP), being a linear chain of phenyl rings, possesses one of the simplest structures. However, its electronic structure and the nature of the blue light emission [2] are still controversial. First-principles local-density approximation studies by Ambrosch-Draxl et al. [3] suggest that the optical properties of PPP can be explained by a purely band picture, with intragap non-linear excitations suppressed by three-dimensional effects. However, recent experimental results on the electroabsorption (EA) and photoinduced absorption (PA) in substituted PPP by Lane et al. [4] are explained by the presence of non-linear excitations, such as singlet and triplet excitons, and charged polarons.The aim of this paper is to clarify the rôle and importance of the low-lying non-linear excitations in PPP by calculating its electronic structure and NLO properties in a realistic Hamiltonian. The EA spectrum compares favourably with recent experiments. We identify the key states which participate in the NLO processes. Moreover, by calculating the particle-hole separation of these states, we identify the band gap as the threshold state whose particle-hole separation increases linearly with oligomer size. This enables a rigorous determination of the band gap to be made.Recently, a two state molecular orbital model was introduced [5] to describe the B 1u and A g states of the phenyl based semiconductors. In the current paper we introduce a more thorough parameterisation of this model by fitting to improved exact Pariser-Parr-Pople model calculations of the molecular building blocks (i.e. benzene and biphenyl) [7]. This model is then solved for oligomers of arbitrary length without further parameterisation. As well as our earlier work, which was the first to use the DMRG method for the phenyl based semiconductors [5, 6], there have been a number of other theoretical calculations on PPP. Brédas has used the VEH pseudopotential technique [8], Champagne et al. have performed Hartree-Fock calcula...

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“…A state of definite Ĉ2 symmetry may then be constructed as follows: [25] and crystalline films (b) [26], (c) [27], (d) [3], (e) [4]. (7), of the essential states for a 15 site oligomer.…”

Section: A Particle-hole Symmetry In the Molecular Orbital Basismentioning

confidence: 99%

Density matrix renormalization group calculations of the low-lying excitations and non-linear optical properties of poly(para-phenylene)

Barford

Bursill

Lavrentiev

1998

J. Phys.: Condens. Matter

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“…There are many experimental studies on the electronic excited states of biphenyl using spectroscopic techniques. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Electronic excitations of biphenyl have been analyzed using the model of a weakly coupled benzene dimer. 33,45,46 In this model, the lowest L b and L a states (also known as the a and p states in another notation) of benzene generate four low-lying singlet states of biphenyl by exciton coupling.…”

Section: Introductionmentioning

confidence: 99%

Electronic excited states and electronic spectra of biphenyl: a study using many-body wavefunction methods and density functional theories

Fukuda

Ehara

2013

Phys. Chem. Chem. Phys.

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The low-lying electronic excited states of biphenyl were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI), complete active space self-consistent field (CASSCF), complete active space perturbation theory of the second-order (CASPT2), and the time-dependent density functional theory (TDDFT). The molecular geometries in the ground and excited states were optimized using the SAC-CI and TDDFT for singlet and triplet states. The energies of vertical excitations, emissions, and adiabatic transitions were calculated. The TDDFT calculations significantly underestimated the excitation energy of the 1(1)B1 state, while the SAC-CI and CASPT2 provided essentially similar results. The present SAC-CI and CASPT2 calculations concluded that the lowest singlet state of isolated biphenyl is the 1(1)B3 state that takes a planar geometry and the second lowest state is the 1(1)B2 state with a twisted geometry. The present results were consistent with the previous experimental findings. The 1(1)B1 state that has a charge-separated biracial character in the vertical excitation relaxed into a planar quinoid structure in which bond alternations were emphasized. The other states took a benzenoid structure. The ultraviolet (UV) absorption and circular dichroism (CD) spectra below 7 eV were calculated with the SAC-CI method. The valence-Rydberg mixings were found to be significant in the second and higher series of excited states.

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“…For the fundamental frequency of the torsional motion, ω 0 , we use data from biphenyl, where ω 0 = 70 cm −1 [71], and apply a mass correction due to the different reduced masses of There is relatively few detailed information concerning the excited electronic states of the dimethyl biphenyl molecule, but the peak of the B band (λ max ∼ 227 nm [72]) is not very displaced from that in biphenyl (λ max ∼ 237.5 nm [73][74][75]), although the peak intensity is smaller. In biphenyl, the excited state has a minimum near θ = 0 and the potential is very flat around the equilibrium geometry [73][74][75].…”

Section: Models and Methodsmentioning

confidence: 99%

“…In biphenyl, the excited state has a minimum near θ = 0 and the potential is very flat around the equilibrium geometry [73][74][75]. We model the excited state in the 2,2'-dimethyl biphenyl potential as a barrierless quartic potential…”

Section: Models and Methodsmentioning

confidence: 99%

Geometrical Optimization Approach to Isomerization: Models and Limitations

et al. 2017

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We study laser-driven isomerization reactions through an excited electronic state using the recently developed Geometrical Optimization procedure [J. Phys. Chem. Lett. 6, 1724Lett. 6, (2015]. The goal is to analyze whether an initial wave packet in the ground state, with optimized amplitudes and phases, can be used to enhance the yield of the reaction at faster rates, exploring how the geometrical restrictions induced by the symmetry of the system impose limitations in the optimization procedure. As an example we model the isomerization in an oriented 2,2'-dimethyl biphenyl molecule with a simple quartic potential. Using long (picosecond) pulses we find that the isomerization can be achieved driven by a single pulse. The phase of the initial superposition state does not affect the yield. However, using short (femtosecond) pulses, one always needs a pair of pulses to force the reaction. High yields can only be obtained by optimizing both the initial state, and the wave packet prepared in the excited state, implying the well known pump-dump mechanism.

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The electronic spectrum of biphenyl

Cited by 36 publications

References 21 publications

Density matrix renormalization group calculations of the low-lying excitations and non-linear optical properties of poly(para-phenylene)

Density matrix renormalization group calculations of the low-lying excitations and non-linear optical properties of poly(para-phenylene)

Electronic excited states and electronic spectra of biphenyl: a study using many-body wavefunction methods and density functional theories

Geometrical Optimization Approach to Isomerization: Models and Limitations

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