Classification of Higher Excited States in (4<i>N</i> + 2)‐Annulenes and Related π‐Electron Systems

Hohlneicher, Georg; Börsch‐Pulm, Birgitt

doi:10.1002/bbpc.19870910922

Cited by 3 publications

(4 citation statements)

References 45 publications

(3 reference statements)

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“…It is well-known that the optical spectra of the smaller acenes are dominated by excitations to three excited electronic states, 1 L a , 1 L b , or 1 B b according to Platt, − that give rise to band systems that are called p, α, and β according to Clar . While the p band is of intermediate intensity, the α band is very weak, and the β band is very strong.…”

Section: Introductionmentioning

confidence: 99%

Electronically Excited States of Higher Acenes up to Nonacene: A Density Functional Theory/Multireference Configuration Interaction Study

Bettinger

Tönshoff

Doerr

et al. 2015

J. Chem. Theory Comput.

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While the optical spectra of the acene series up to pentacene provide textbook examples for the annulation principle, the spectra of the larger members are much less understood. The present work provides an investigation of the optically allowed excited states of the acene series from pentacene to nonacene, the largest acene observed experimentally, using the density functional based multireference configuration method (DFT/MRCI). For this purpose, the ten lowest energy states of the B2u and B3u irreducible representations were computed. In agreement with previous computational investigations, the electronic wave functions of the acenes acquire significant multireference character with increasing acene size. The HOMO → LUMO excitation is the major contributor to the (1)La state (p band, B2u) also for the larger acenes. The oscillator strength decreases with increasing length. The (1)Lb state (α band, B3u), so far difficult to assign for the larger acenes due to overlap with photoprecursor bands, becomes almost insensitive to acene length. The (1)Bb state (β band, B3u) also moves only moderately to lower energy with increasing acene size. Excited states of B3u symmetry that formally result from double excitations involving HOMO, HOMO-1, LUMO, and LUMO+1 decrease in energy much faster with system size. One of them (D1) has very small oscillator strength but becomes almost isoenergetic with the (1)La state for nonacene. The other (D2) also has low oscillator strength as long as it is higher in energy than (1)Bb. Once it is lower in energy than the (1)Bb state, both states interact strongly resulting in two states with large oscillator strengths. The emergence of two strongly absorbing states is in agreement with experimental observations. The DFT/MRCI computations reproduce experimental excitation energies very well for pentacene and hexacene (within 0.1 eV). For the larger acenes deviations are larger (up to 0.2 eV), but qualitative agreement is observed.

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Section: Introductionmentioning

confidence: 99%

Electronically Excited States of Higher Acenes up to Nonacene: A Density Functional Theory/Multireference Configuration Interaction Study

Bettinger

Tönshoff

Doerr

et al. 2015

J. Chem. Theory Comput.

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“…Excluding single excitations in RAS3 enhances convergence by eliminating redundancy. This active space is denoted as RAS(n,0,2;0, 11,5), where n = 14, 15, 16, and 17 for Fe 2+ , Co 2+ , Ni 2+ , and Cu 2+ porphyrins, respectively. For FeCl 2+ , we conducted two calculations with two active space choices, one with the double d shell (3d′) orbitals included in the RAS3 partition, and the other using a CAS (17,13) active space that omitted 3d′ to make room for two additional σ-type occupied bonding orbitals in the RAS2 partition.…”

Section: ■ Methodsmentioning

confidence: 99%

“…These labels were initially introduced by Platt 7 and Moffitt 8,9 and later elaborated by Heilbronner and Murrell 10 and Hohlneicher. 11 They apply generally to all cyclic π-electron systems, including porphyrins, that possess a closed-shell ground state derived from an uncharged or charged (4N+2)-electron perimeter, 12−15 whereas the present labels Q and B are specific for porphyrins.…”

Section: ■ Introductionmentioning

confidence: 99%

“…To avoid confusion, we note that in the early more generally applicable “perimeter model” for cyclic π-electron systems, the first two doubly degenerate bands presently called Q and B would be designated as L and B . These labels were initially introduced by Platt and Moffitt , and later elaborated by Heilbronner and Murrell and Hohlneicher . They apply generally to all cyclic π-electron systems, including porphyrins, that possess a closed-shell ground state derived from an uncharged or charged (4 N +2)-electron perimeter, − whereas the present labels Q and B are specific for porphyrins.…”

Section: Introductionmentioning

confidence: 99%

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Ab Initio Calculation of UV–vis Absorption of Parent Mg, Fe, Co, Ni, Cu, and Zn Metalloporphyrins

Ganguly,

Havlas,

Michl

2024

Inorg. Chem.

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Relativistic restricted active space (RAS) second-order multireference perturbation theory (MRPT2) methods, incorporating spin–orbit (SO) coupling perturbatively via state interaction (SO-MRPT2/RASSCF), were used to reproduce the absorption spectra of parent metalloporphyrins containing the Mg2+, Zn2+, Co2+, Ni2+, Cu2+, or FeCl2+ ions in the 12,500–40,000 cm–1 region. Particular attention was paid to the interaction between the porphyrin ring and the metal 3d electrons in states of different multiplicities (we used metal 3d and double d-shell or 3d′ orbitals). For this class of compounds, the N-electron valence state perturbation theory (NEVPT2) method is superior to the complete active space perturbation theory (CASPT2) and successfully reproduces the energies of all four characteristic transitions (Q, B, N, and L) of closed-shell metalloporphyrins. Inclusion of SO coupling was found to have very little effect on excitation energies and oscillator strengths. For FeCl2+ porphyrin, we treated ligand-to-metal charge-transfer (LMCT; π,d), metal ligand field (d,d), and metal-to-ligand charge-transfer (MLCT; d,π*) transitions within the same framework. The broad and intense spectral features associated with its B (Soret) band are attributed to multiconfigurational LMCT (d,π*) bands involving strong metal–ligand orbital mixing.

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Higher electronically excited states of phenanthrene, carbazole and fluorene

Gudipati¹,

Daverkausen²,

Maus³

et al. 1994

Chemical Physics

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Classification of Higher Excited States in (4N + 2)‐Annulenes and Related π‐Electron Systems

Cited by 3 publications

References 45 publications

Electronically Excited States of Higher Acenes up to Nonacene: A Density Functional Theory/Multireference Configuration Interaction Study

Electronically Excited States of Higher Acenes up to Nonacene: A Density Functional Theory/Multireference Configuration Interaction Study

Ab Initio Calculation of UV–vis Absorption of Parent Mg, Fe, Co, Ni, Cu, and Zn Metalloporphyrins

Higher electronically excited states of phenanthrene, carbazole and fluorene

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