Search results for "iTED"
showing 10 items of 2408 documents
Singlet oxygen generation in PUVA therapy studied using electronic structure calculations
2009
Abstract The ability of furocoumarins to participate in the PUVA (Psoralen + UV-A) therapy against skin disorders and some types of cancer, is analyzed on quantum chemical grounds. The efficiency of the process relies on its capability to populate its lowest triplet excited state, and then either form adducts with thymine which interfere DNA replication or transfer its energy, generating singlet molecular oxygen damaging the cell membrane in photoactivated tissues. By determining the spin–orbit couplings, shown to be the key property, in the intersystem crossing yielding the triplet state of the furocoumarin, the electronic couplings in the triplet–triplet energy transfer process producing …
Theoretical CASPT2 study of the excited state double proton transfer reaction in the 7-azaindole dimer
2006
Accurate CASPT2 calculations on the excited state double proton transfer reaction in the 7-azaindole dimer have been performed on different symmetric and asymmetric pathways along the protons interchange. The presence of a conical intersection connecting the initially photoinduced singlet excited state with a charge transfer state leading both to asymmetric ionic and neutral structures promotes a step-wise mechanism, probably taking place through the ionic intermediate. The concerted path is computed slightly higher in energy in the gas phase.
Theoretical characterization of the absorption spectra of phenanthrene and its radical cation
2003
The vertical absorption spectra of phenanthrene and its radical cation have been studied theoretically by means of a multiconfigurational second-order perturbation approach. Singlet-singlet transition energies and oscillator strengths, and singlet-triplet excitation energies have been studied in the absorption spectrum of phenanthrene up to 6 eV. The absorption spectrum of the pehnanthrene radical cation has been computed up to 3.4 eV. The results obtained confirm previous assignments and also lead to new interpretations of the main features of the spectra of these systems.
Energetics and Dynamics of Naphthalene Polyaminic Derivatives. Influence of Structural Design in the Balance Static vs Dynamic Excimer Formation
2003
Two new fluorescent macrocyclic structures bearing two naphthalene (Np) units at both ends of a cyclic polyaminic chain were investigated with potentiometric, fluorescence (steady-state and time-resolved) and laser flash photolysis techniques. The fluorescence emission studies show the presence of an excimer species whose formation depends on the protonation state of the polyamine chains implying the existence of a bending movement (occurring in both the ground and in the first singlet excited state), which allows the two naphthalene units to approach and interact. For comparison purposes, one bis-chromophoric compound containing a rigid chain (piperazine unit) was also investigated. Its em…
Electronic Spectra of 2,2‘-Bithiophene and 2,2‘:5‘,2‘ ‘-Terthiophene Radical Cations: A Theoretical Analysis
2001
Analysis of the electronic spectra of 2,2‘-bithiophene and 2,2‘:5‘,2‘ ‘-terthiophene radical cations has been performed by using multiconfigurational second-order perturbation theory (CASPT2). Atomic natural orbital (ANO) type basis sets of split valence quality, including polarization functions on all heavy atoms, have been used. In agreement with experimental data, in the energy range below the lowest optically allowed transition of the respective neutral system, theoretical results predict two main absorption bands for both cations. The 22Au and 32Au states computed at 1.94 and 2.80 eV, respectively, are related to the corresponding band maxima recorded for bithiophene cation. The 12B1 s…
Interpretation of the electronic absorption spectrum of free base porphin by using multiconfigurational second-order perturbation theory
1998
Abstract Multiconfigurational second-order perturbation (CASPT2) calculations have been performed on the low-lying optically allowed valence excited states of the free base porphin molecule in order to assign the four lowest bands of the spectrum. The low-lying triplet states have also been characterized. A basis set of the atomic natural orbital type of split-valence plus polarization quality for first-row atoms has been employed. Polarization functions are important for an accurate description of the transitions. These CASPT2 results provide a consistent picture of the experimental spectrum. Each band of the spectrum up to 4.5 eV is composed of a pair of states, which become degenerate in…
On the vertical excitation energy of cyclopentadiene
2004
The vertical excitation energy for the lowest valence pi--pi(*) transition of cyclopentadiene is investigated. Using a combination of high-level theoretical methods and spectroscopic simulations, the vertical separation at the ground state geometry is estimated to be 5.43+/-0.05 eV. This value is intermediate between those calculated with coupled-cluster and multireference perturbation theory methods and is about 0.13 eV higher than the observed maximum in the absorption profile.
A Theoretical Insight into the Photophysics of Acridine
2001
The electronic absorption and emission spectra of acridine have been studied by means of a multiconfigurational second-order perturbation method (CASSCF/CASPT2) and its multistate extension (MS-CASPT2). The low-lying valence singlet and triplet π → π* and n → π* excited states have been computed. The location of the lowest Rydberg state (3s) has been also estimated. By optimization of the geometries of the ground and low-lying excited states and the calculation of transition energies and properties, the obtained results lead to a complete analysis and assignment of the available experimental singlet−singlet and triplet−triplet absorption spectra and to the description of the basic features …
Theoretical Analysis of the Excited States in Maleimide
2003
The electronic excited states of maleimide have been studied using multiconfigurational second-order perturbation theory in its multistate formulation (MS-CASPT2) and extended atomic natural orbita...
Pyrene-benzoylthiophene exciplexes as selective catalysts for the [2+2] cycloaddition between cyclohexadiene and styrenes.
2007
Efficient intramolecular fluorescence quenching in pyrene−benzoylthiophene systems leads to formation of exciplexes. These species interact with 1,3-cyclohexadiene (or styrenes), leading to reactive excited triplexes. The overall process affords [2+2] cross-cycloadducts with an average yield of 57%.