Application of vibrational correlation formalism to internal conversion rate: case study of Cu(n) (n = 3, 6, and 9) and H2/Cu3.

This work reports non-radiative internal conversion (IC) rate constants obtained for Cun with n = 3, 6, and 9 and H2 on Cu3. The Time-Dependent Density Functional Theory (TDDFT) method was employed with three different functionals in order to investigate the electronic structures and the absorption spectra. The performance of the generalized gradient approximation of Perdew, Burke and Ernzerhof (PBE) and the hybrid B3LYP and PBE0 exchange correlation functionals in combination with the SVP and the def2-TZVP basis sets was examined. TDDFT results were used as input data to compute internal conversion rate constants. For this purpose, we have developed a program package. A description of the theoretical background used in our numerical implementation and the program input file is presented. In view of future applications of this program package in photoinduced catalysis, we present the analysis of the IC rate processes for the photodissociation of H2 on Cu3. These results showed the applicability of the method and the computational program to identify the vibrational modes in transition metal clusters giving rise to the largest IC rate constant due to their interactions with the excited electronic states occurring in the hot-electron induced dissociation phenomena.

Antioxidant efficiency of oxovitisin, a new class of red wine pyranoanthocyanins, revealed through quantum mechanical investigations.

Oxovitisin is a natural antioxidant present in aged wine and comes from the chemical transformation undergone by anthocyanins and pyranoanthocyanins. Its antioxidant radical scavenging capacity was theoretically explored by density functional theory (DFT)/B3LYP methods. The O-H bond dissociation energy (BDE), the ionization potential (IP), the proton affinity (PA), and the metal-oxovitisin binding energy (BE) parameters were computed in the gas-phase and in water and benzene solutions. Results provided molecular insight into factors that influence radical scavenging potential of this new class of anthocyanins.

A TDDFT investigation of bay substituted perylenediimides: absorption and intersystem crossing.

The conformational structure and electronic spectra properties of a series of bay substituted perylenediimides (PDI) derivatives have been investigated by means of density functional theory (DFT) and time-dependent DFT. The B3LYP and PBE0 hybrid exchange-correlation functionals were applied in conjunction with the double-ζ quality SVP basis set. These compounds are interesting for organic materials science and as photosensitizers in cancer phototherapy (PDT), because of their intense absorption in the visible region. Results show that the substitution at the bay position of the PDI parent molecule with N-alkyl groups shifts the absorption maxima towards the red part of the visible spectrum (around 650-700 nm) as required for the applications in PDT. The main PDT action mechanisms have been investigated by computing of electron affinities, ionization potentials, triplet energies and spin-orbit matrix elements between singlet and triplet excited states.

A Theoretical Study of Brominated Porphycenes: Electronic Spectra and Intersystem Spin-Orbit Coupling.

In this paper, a time-dependent density functional theoretical study (TDDFT) has been carried out for brominated 2,7,12,17-tetra-n-propylporphycenes. Their potential therapeutic use in photodynamic therapy (PDT), a noninvasive medical treatment of cancer diseases, is due to the strong absorbance in the red part of the visible spectrum and the presence of heavy atoms (bromine). The prediction of electronic spectra for photosensitizer molecules can be a valuable tool in the design of drugs for application in PDT. Singlet and triplet vertical excitation energies have been calculated by means of the nonempirical hybrid functional PBE0 in conjunction with a split valence basis set (SVP), on previously optimized, at the density functional level of theory, ground state geometries. In particular, the quantum-chemical simulation of their absorption electronic spectra, both in vacuo and in solvent environments (dichloromethane and bromobenzene), has evidenced the red shift maxima wavelengths for the Q bands (or lower energy bands) with an increasing number of bromine atoms, in agreement with experimental results. The mean absolute deviation for the Q-electronic bands is about 0.3 eV. Calculated vertical triplet energies are between 1.04 (for tetra-brominated derivative) and 1.20 eV (for dibrominated derivative). The influence of bromine atoms on intersystem spin crossing has been investigated by applying a computational code which calculates spin-orbit matrix elements between singlet and triplet excited state wave functions weighted by the TDDFT transition coefficients.