Estudos teóricos da fotoisomerização de butadieno e butadieno substituído.

Abstract

The interaction of light with matter is really important in several processes of nature. Photons are employed by natural systems as energy donors or as information elements. The energy from photons, for example, is used in the Z-E isomerization of the C = C bond of the butadiene molecule. Isomerization consists of a photochemical process widely explored and it is the fundamental step of many photobiological processes, such as vision, light-induced ion bomb and phototaxis. This work aims to obtain stationary points from the surface of the potential energy of the butadiene molecules substituted with the Cl group, butadiene substituted with carbonyl (CHO), butadiene substituted with the amine group (NH2) and butadiene. The surface description provides a model for understanding the influence of the groups on the geometry and the photoisomerization process. As a starting point for the investigations in the excited state, the configurations of the molecules corresponding to minima in the potential energy surface of the ground state have been mapped with the CASSCF method. For the carbonyl substituted butadiene molecule, an active space of six orbitals and six electrons was chosen, while, for the chlorinated substituted butadienes, amine substituted butadiene and butadiene, an active space of four orbitals and four electrons was chosen. In addition to the minima in the excited state, four minima have been found at the conic intersection (CI) for chlorobutadiene, three minima at CI for butadiene, three minima at CI for pentadienal and four minima at CI for the amine-butadiene molecule. When comparing the results of the global minimum at the CI of the substituted butadiene molecules with the results for the butadiene molecule, it is realized that the substituents do not significantly alter the geometry of the intersection of the butadiene. However, a CI has been found which is possibly associated with the chlorine dissociation process.Furthermore, two CI's for the amine substituted butadiene are possibly associated with the photoisomerization control, as only the double bond next to the substituent seems to be isomerized.