Electronic Excitations in Pyrrole: A Test Case for Determination of Chromophores in the Chromogenic Effects of Neurotoxic Hydrocarbons by Time-Dependent Density Functional Theory and Single-Excitation Configuration Interaction Methods

Zhan, Chang-Guo; Dixon, David A.

doi:10.1006/jmsp.2002.8622

Cited by 12 publications

(8 citation statements)

References 57 publications

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“…Solvent effects were not included due to the size of the calculation, but could be estimated using the difference between the experimentally-observed and DFT-calculated λ. For Car •+ , the difference between the maximum observed experimentally in PS II (982 nm) and calculated in the gas phase with the TD-DFT method (829 nm) was 0.24 eV, a value similar to typical errors of 0.2 – 0.5 eV in DFT calculations 33–36. The difference for #Car • (4) was 0.4 eV.…”

Section: Experimental Methodssupporting

confidence: 72%

Formation of Carotenoid Neutral Radicals in Photosystem II

et al. 2009

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β-carotene radicals produced in the hexagonal pores of the molecular sieve Cu(II)-MCM-41 were studied by ENDOR and visible/near IR spectroscopies. ENDOR studies showed that neutral radicals of β-carotene were produced in humid air under ambient fluorescent light. The maximum absorption wavelengths of the neutral radicals were measured and were additionally predicted by using time-dependent density functional theory (TD-DFT) calculations. An absorption peak at 750 nm, assigned to the neutral radical with a proton loss from the 4(4') position of the β-carotene radical cation in Cu(II)-MCM-41, was also observed in photosystem II (PS II) samples using near-IR spectroscopy after illumination at 20 K. This peak was previously unassigned in PS II samples. The intensity of the absorption peak at 750 nm relative to the absorption of chlorophyll radical cations and β-carotene radical cations increased with increasing pH of the PS II sample, providing further evidence that the absorption peak is due to the deprotonation of the β-carotene radical cation. Based on a consideration of possible proton acceptors that are adjacent to β-carotene molecules in photosystem II, as modeled in the X-ray crystal structure of Guskov et al. Nat. Struct. Mol. Biol. 2009, 16, 334-342, an electron-transfer pathway from a β-carotene molecule with an adjacent proton acceptor to P680•+ is proposed.

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Section: Experimental Methodssupporting

confidence: 72%

Formation of Carotenoid Neutral Radicals in Photosystem II

et al. 2009

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“…Because of this, its electronic states and subsequent photochemistry have been intensively studied both experimentally and theoretically. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In particular its photochemistry is very rich showing ultrafast 13 decomposition into a variety of products after UV photoexcitation. 1,11,14,19 Femtosecond time-resolved experiments have established that the deactivation of UV-excited pyrrole to the ground state occurs on a very short time scale, 13 which combined with its low luminescence quantum yields, 20 implies the dominance of internal conversion processes.…”

Section: Introductionmentioning

confidence: 99%

Dynamics starting at a conical intersection: Application to the photochemistry of pyrrole

Sellner

Barbatti

Lischka

2009

The Journal of Chemical Physics

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The photochemical ring opening process in pyrrole has been investigated by performing classical on-the-fly dynamics using the multiconfiguration self-consistent field method for the computation of energies and energy gradients. As starting point for the dynamics the conical intersection corresponding to the ring-puckered ring-opened structure, determined previously [Barbatti et al., J. Chem. Phys. 125, 164323 (2006)], has been chosen. Two sets of initial conditions for the nuclear velocities were constructed: (i) nuclear velocities in the branching (g,h) plane of the conical intersection and (ii) statistical distribution for all atoms. Both sets of initial conditions show very similar results. Reactive trajectories are only found in a very limited sector in the (g,h) plane and reaction products are very similar. Within the simulation time of 1 ps, ring opening of pyrrole to the biradical NH=CH-CH(*)-CH=CH(*) chain followed by ring closure to a substituted cyclopropene structure (NH=CH-C(3)H(3)) is observed. The computed structural data correlate well with the experimentally observed dissociation products.

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“…As in pyrrole, the aromatic ring in 2,5-DMP is planar and the molecule has C 2v symmetry; calculations indicate only very minor structural differences between the ring in pyrrole and in 2,5-DMP. 17 Absorption of liquid 2,5-DMP is used as a standard for observing the presence of 2,5-DMP (or its adducts) in biochemical studies. 18 However, there have been very few reported studies of the effects-photochemically, or from the viewpoint of the electronic spectrum-of adding two methyl groups to the pyrrole ring.…”

Section: Introductionmentioning

confidence: 99%

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

Cronin¹,

Nix²,

Devine³

et al. 2006

Phys. Chem. Chem. Phys.

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The photodissociation dynamics of 2,5-dimethylpyrrole (2,5-DMP) has been investigated following excitation at 193.3 nm and at many near ultraviolet (UV) wavelengths in the range 244 < lambda(phot) < 282 nm using H Rydberg atom photofragment translational spectroscopy (PTS). Complementary UV absorption and, at the longest excitation wavelengths, one photon resonant multiphoton ionisation spectra of 2,5-DMP are reported also; analysis of the latter highlights the role of methyl torsional motions in promoting the parent absorption. The deduced fragmentation dynamics show parallels with that reported recently (B. Cronin, M. G. D. Nix, R. H. Qadiri and M. N. R. Ashfold, Phys. Chem. Chem. Phys., 2004, 6, 5031) for the bare pyrrole molecule. Excitation at the longer wavelengths leads to (vibronically induced) population of the 1(1)A(2)(pisigma*) excited state of 2,5-DMP, but once lambda(phot) decreases to approximately 250 nm stronger, dipole allowed transitions start to become apparent in the parent absorption. All total kinetic energy release (TKER) spectra of the H + 2,5-dimethylpyrrolyl (2,5-DMPyl) fragments measured at lambda(phot)> or=244 nm show a structured fast component, many of which are dominated by a peak with TKER approximately 5100 cm(-1); analysis of this structure reveals lambda(phot) dependent population of selected vibrational levels of 2,5-DMPyl, and enables determination of the N-H bond strength in 2,5-DMP: D(0) = 30 530 +/- 100 cm(-1). Two classes of behaviour are proposed to account for details of the observed energy partitioning. Both assume that N-H bond fission involves passage over (or tunnelling through) a small exit channel barrier on the 1(1)A(2) potential energy surface, but differ according to the vibrational energy content of the photo-prepared molecules. Specific parent out-of-plane skeletal modes that promote the 1(1)A(2)-X(1)A(1) absorption appear to evolve adiabatically into the corresponding vibrations of the 2,5-DMPyl products. Methyl torsions can also promote the 1(1)A(2)<-- X(1)A(1) absorption in 2,5-DMP, and provide a means of populating a much higher density of excited vibrational levels than in pyrrole. Such excited levels are deduced to dissociate by redistributing the minimum amount of internal energy necessary to overcome the exit channel barrier in the N-H dissociation coordinate. Coupling with the ground state surface via a conical intersection at extended N-H bond lengths is proposed as a further mechanism for modest translational --> vibrational energy transfer within the separating products. The parent absorption cross-section increases considerably at wavelengths approximately 250 nm, and PTS spectra recorded at lambda(phot)< or = 254 nm display a second, unstructured, peak at lower TKER. As in pyrrole, this slower component is attributed to H atoms from the unimolecular decay of highly vibrationally excited ground state molecules formed via radiationless decay from photo-excited states lying above the 1(1)A(2) state.

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Electronic Excitations in Pyrrole: A Test Case for Determination of Chromophores in the Chromogenic Effects of Neurotoxic Hydrocarbons by Time-Dependent Density Functional Theory and Single-Excitation Configuration Interaction Methods

Cited by 12 publications

References 57 publications

Formation of Carotenoid Neutral Radicals in Photosystem II

Formation of Carotenoid Neutral Radicals in Photosystem II

Dynamics starting at a conical intersection: Application to the photochemistry of pyrrole

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

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