Leonardo T. Ueno

Photophysics and spectroscopic properties of zinc phthalocyanine revisited using quantum chemistry

This study provides a theoretical evaluation of the photophysical behavior of zinc phthalocyanine (ZnPc) using density functional theory (DFT) and its time-dependent (TD-DFT) approach, based on the combination of the B3LYP hybrid functional and the 6-311+G(d,p) basis set. The influence of solvation was estimated using IEFPCM (integral equation formalism approach of polarizable continuum model) considering DMSO (dimethyl sulfoxide) as solvent. The simulated absorption spectra were based in the calculation of the first 40 excited states being that the eight most intense peaks could be assigned to the Q and Soret (B) bands. Fluorescence emission wavelength and radiative lifetime were calculated using the TD-DFT approach and compared to experimental data. The ZnPc intersystem crossing (ISC) phenomena was attributed to spin-orbit coupling induced by Zn2+ since the adjacent singlet and triplet states have the same orbital symmetry. The phosphorescence data in gas phase were also compared.

Synthesis and spectroscopic characterization of two tetrasubstituted cationic porphyrin derivatives.

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by 1H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed.

Influence of gold nanoparticles applied to catalytic hydrogenation of acetophenone with cationic complexes containing ruthenium

Herein the catalytic activity of cationic ruthenium(II) complexes [Ru]+ is described in the presence of gold nanoparticles (AuNPsn−) in the transfer hydrogenation of acetophenone, to produce phenylethanol. The catalytic activity of the complexes, with a general formula cis-[RuCl(CH3OH)(P–P)(N–N)]+ or cis-[RuCl(CH3OH)(P)2(N–N)]+ {where: P = triphenylphosphine (PPh3); P–P = 1,1-bis(diphenylphosphino)methane (dppm); 1,2-bis(diphenylphosphino)ethane (dppe); 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb); N–N = 2,2′-bipyridine; 4,4′-dimethyl-2,2′-bipyridine} was investigated in the presence of AuNPsn−. The interaction between [Ru]+ and AuNPsn− citrate capped is an electrostatic interaction, by a self-assembly processes, to produce a supramolecular species, labeled as [Ru]+/AuNPsn−. This non-covalent interaction has no effect over the chemical and physical chemical parameters of the complexes, which provides a good point of comparison in the presence and absence of AuNPsn−. The AuNPsn− alone have no catalytic activity in the transfer hydrogenation of acetophenone within 24 h of reaction. However, the AuNPsn− have improved the catalytic activity of the complexes that have biphosphines with tensioned or large bite angle, while for the complexes that have biphosphines with a strong chelate effect a decrease in the catalytic activity was observed. The evidence is supported by experimental values of the yields of the hydrogenated product and DFT calculations of the “RuP–P” intermediates. Suitable crystals of cis-[RuCl2(dppe)(bipy)], cis-[RuCl2(dppp)(bipy)] and cis-[RuCl(CH3OH)(dppb)(bipy)](PF6) were obtained and the X-ray structures are presented here.

Comparative study of small boron, silicon and germanium clusters: B(m)Si(n) and B(m)Ge(n) (m + n = 2-4).

AbstractChemically speaking, atomic clusters are very rich, allowing their application in a broad range of technological areas such as developing functional materials, heterogeneous catalysis, and building optical devices. In this work, high level computational chemistry methods were used in a systematic manner to improve the characterization of small clusters formed by boron, silicon, germanium, mixed boron/silicon, and mixed boron/germanium. Calculations were carried out with both ab initio [MP2 and CCSD(T)] and density functional (B3LYP) methods with extended basis sets. The CCSD(T) results were then extrapolated to the complete basis set (CBS) limit. Finally, geometrical parameters, vibrational frequencies, and relative energies were then obtained and compared to data presented in the literature. Graphical AbstractSmall boron, silicon and germanium clusters: BmSin and BmGen (m + n = 2–4)