| 1. |
- Baev, Alexander, et al.
(författare)
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Optical limiting properties of Zinc- and Platinum-based organometallic compounds
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:36, s. 7406-7416
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Tidskriftsartikel (refereegranskat)abstract
- Optical power limiting is theoretically studied using an approach that combines quantum electronic structure calculations of multiphoton excitations and classical calculations of dynamical wave propagation. We illustrate the capability of such a combined approach by presenting results for a couple of organometallic compounds; basic metal-base porphyrins, vinylphenylamine porhyrin, and the so-called type IVc platinum compound. A comparative analysis of their electronic properties related to nonlinear absorption of electromagnetic radiation and their optical limiting capability has been performed based on dynamical simulations of the nonlinear pulse propagation taking account of resonant as well as off-resonant effects. Several key features and rate-limiting steps in the transmission have been examined in relation to various characteristics of the pulse. It is found that the resonant vs off-resonant conditions, the saturation conditions and the dephasing play critical roles for the nonlinear transmission. The saturation effects are sensitive to the pulse duration, the inter-system crossing rate and the quenching of the higher triplet state. The inter-system crossing rate has to be comparable with the inverse pulse duration in order to boost the stepwise two-photon channel associated with singlet-singlet followed by triplet-triplet transitions. It is illustrated that structure-to-property relations of the rate-limiting steps serve as important criteria for choices of compounds suitable for the application of interest.
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| 2. |
- Baev, Alexander, et al.
(författare)
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Upconverted lasing based on many-photon absorption : an all dynamic description
- 2004
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 21:2, s. 384-396
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Tidskriftsartikel (refereegranskat)abstract
- A theory is developed for the propagation through a nonlinear medium of strong pump and amplifiedspontaneous-emission pulses. The theory is based on a solution of the density matrix equations that aims at providing an adequate treatment of the nonlinear polarization of the material without addressing the Taylor expansion over the powers of intensity. The theory has been applied for modeling of three-photon absorption induced upconverted stimulated emission of organic molecules in solvents. Numerical results are presented for the organic chromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulfonyl) stilbene dissolved in dimethyl sulfoxide. The results are in good agreement with available experimental results.
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| 3. |
- Kashtanov, Stepan, et al.
(författare)
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Characterization of aza-fullerene C58N2 isomers by X-ray spectroscopy
- 2003
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 371:02-jan, s. 98-104
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron and near-edge X-ray absorption fine-structure spectra (NEXAFS) of four isomers of C58N2 are predicted by means of density-functional theory calculations. A strong isomer dependence for both types of spectra are found. The spectroscopic findings are discussed in conjunction with results from electronic and geometric structure optimizations.
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| 4. |
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| 5. |
- Rubio Pons, Oscar, et al.
(författare)
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A butterfly like motion as a clue to the photophysics of thioxanthone
- 2006
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier BV. - 1010-6030 .- 1873-2666. ; 179:3, s. 298-304
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical, quantum-chemical study of the thioxanthone (TX) molecule has been performed at the MP2 and CASPT2 levels of theory. Geometries, absorption energies, and transition and state properties have been investigated. Two conformers have been found very close in energy with planar (P) and non-planar (NP) structures, the latter characterized by a dihedral angle theta = 173.3 degrees representing the bend of the side benzene rings and an out-of-plane angle theta=4 degrees of the C=O bond. Large changes in the relative positions and properties of the two low-lying electronic absorption bands, pi pi* and n pi*, are computed when changing the conformation. As a consequence of the analysis of the TX absorption spectrum it is suggested that TX should be viewed as dynamically changing its conformation between the planar and the non-planar conformations. We coined such behavior as a "butterfly like motion". This dynamic view of the TX structure enables a plausible explanation of the photophysical properties observed for the system.
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| 6. |
- Rubio Pons, Oscar, et al.
(författare)
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Ab initio calculations of vibronic activity in phosphorescence microwave double resonance spectra of para-dichlorobenzene
- 2005
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 113:1, s. 15-27
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Tidskriftsartikel (refereegranskat)abstract
- The phosphorescence spectrum of p-dichlorobenzene has been calculated using multiconfiguration self-consistent-field wave functions and the quadratic response technique. Attention has been paid to the intensity distribution of the singlet-triplet (B-3(1u)->(1)A(g)) transition through a number of vibronic subbands. The second order spin-orbit coupling (SOC) contribution to the spin splitting of the B-3(1u) ((3)pi pi*) state is found to be almost negligible, and the calculations therefore provide a good estimate for the zero-field splitting (ZFS) parameters based only on the electron spin-spin coupling expectation values. Nuclear quadrupole resonance constants for the different Cl isotopes are also calculated to accomplish the ZFS assignment. The electric dipole activity of the spin sublevels in the triplet singlet transitions to the ground-state vibrational levels is estimated by calculations of derivatives using distorted geometries which are shifted from the equilibrium position along different vibrational modes. A vibrational analysis of the phosphorescence spectrum, based on the SOC-induced mixing of the singlet and triplet states calculated along different vibrational modes, provides reasonable agreement with experimental data.
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| 7. |
- Rubio Pons, Oscar, et al.
(författare)
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CASSCF calculations of triplet-state properties : Applications to benzene derivatives
- 2003
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 101:13, s. 2103-2114
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Tidskriftsartikel (refereegranskat)abstract
- We illustrate the capability of the complete active space self-consistent field method by Roos and co-workers for calculations of triplet state properties. We report phosphorescence lifetimes, zero-field splitting parameters, and nuclear quadrupole coupling constants for the lowest triplet state of a variety of benzene derivatives.
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| 8. |
- Rubio Pons, Oscar
(författare)
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Charge-transfer excitations and phtophysical properties of molecular building blocks
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports a state-of-the-art theoretical study of photophysical properties of organic charge-transfer aromatic molecules. These molecules are building blocks of molecular functional materials used in modern photonics technology and play essential roles in chemistry and biology in general. A good understanding of these systems is thus important. The theoretical results for permanent dipole moments of some substituted benzenes have been obtained using the coupled cluster singles and doubles (CCSD) method. The performance of density functional theory (DFT) for the geometry and electronic properties has been compared with that of traditional ab initio methods, such as Hartree-Fock, second-order Möller Plesset perturbation theory (MP2), CCSD and CCSD(T). Limitations of the DFT methods for charge transfer molecules have been demonstrated. The multi-configuration self-consistent field (MCSCF) method has been applied to understand properties of the triplet states of benzene derivatives by studying their phosphorescence with the inclusion of contributions from vibronic coupling. It has also been employed to calculate the photophysics of the thioxanthone molecule containing three benzene rings in combination with the CASPT2 method, resolving a long-standing problem concerning the possible stable conformations of the molecule. With knowledge of the building blocks a series of porphyrin derivatives with exceptionally large two-photon absorption cross sections were designed, and proposed for use in bioimaging applications. The static and dynamic properties of a few zinc and platinum organometallic compounds, being possible candidates for optical limiting devices, have also investigated.
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| 9. |
- Rubio-Pons, Oscar, et al.
(författare)
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Effects of Conjugation Length, Electron Donor and Acceptor Strengths on Two-Photon Absorption Cross Sections of Asymmetric Zinc-Porphyrin Derivatives
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 124:9, s. 094310-
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Tidskriftsartikel (refereegranskat)abstract
- Exceptionally large two-photon absorption cross sections at the infrared region have been revealed by time-dependent density functional theory calculations for asymmetric charge-transfer conjugated zinc-porphyrin derivatives. The largest two-photon cross section is found to be more than one order of magnitude larger than for the conventional two-photon active organic molecules. The calculations show that the formation of strong charge-transfer states depends on the length of the conjugation bridge between the zinc-porphyrin core and the electron donor/acceptor. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor/acceptor.
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| 10. |
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| 11. |
- Rubio Pons, Oscar
(författare)
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Photophysical Properties of Organic and Organometallic molecules
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Highly correlated quantum chemical methods have been appliedto study the photophysical properties of substituted benzenes.With the inclusion of spin-orbit coupling, the phosphorescencesof these molecules have been calculated usingMulti-CongurationalSelf- Consistent Field (MCSCF) quadraticresponse theory. The Herzberg-Teller approximation has beenadopted to evaluate the vibronic contributions tophosphorescence. The performance of hybrid density functional theory (DFT) atthe B3LYP level is examined in comparison to the MP2, CCSD andCCSD(T) methods for the geometry and permanent dipole moment ofp-aminobenzoic acid. The time-dependent DFT/B3LYP method isapplied to calculate the two-photon absorption of a series ofZinc-porphyrin derivatives in combination with a two-statemodel. The transitions between excited singlet and tripletstates of Zinc and Platinum based organometallic compounds havebeen computed using DFT quadratic response theory. The resultsare used to simulate the non-linear propagation of laser pulsesthrough these materials utilizing a dynamical wave propagationmethod.
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| 12. |
- Rubio-Pons, Oscar, et al.
(författare)
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The permanent dipole moment of gas-phase para-amino benzoic acid revisited
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:1, s. 157-161
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Tidskriftsartikel (refereegranskat)abstract
- A study of permanent dipole moment of para-amino benzoic acid (PABA) by using various computational methods, was carried out. The dipole meoments of PABA was computed at Hartree-Fock, second-order Mφller-Plesset perturbation (MP2), coupled cluster singles and doubles (CCSD), triple corrections CCSD(T) and hybrid density functional theory at B3LYP level with different basis sets. It was found that the electron density by B3LYP resulted in large charge separation in the charge transfer molecules. It was stated that the best dipole moments were obtained at CCSD and CCSD(T) levels experiments.
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