Efeitos de campo cristalino nas propriedades ópticas lineares de materiais moleculares: sob a perspectiva de átomos e blocos construtores orgânicos

Abstract

In order to rationally design new molecular materials with desirable linear optical properties, such as refractive index or birefringence, it was investigated how atomic and functional-group polarizability tensors of prototypical molecules respond to crystal field effects. By building finite aggregates of urea, succinic acid, p-nitroaniline, 4-mercaptopyridine or methylbenzoate, and by partitioning the cluster electronic density using quantum theory of atoms in molecules, it was possible to extract atoms and functional groups from the aggregates and estimate their polarizability enhancements with respect to values calculated for molecules in isolation. The isotropic polarizability and its anisotropy for the molecular building blocks are used to understand the functional-group sources of optical properties in these model systems, which could help the synthetic chemist to fabricate efficient materials. This analysis is complemented by benchmarking density functionals for atomic distributed polarizabilities in gas phase, by comparing the results with refractive-index calculations under periodic boundary conditions, and by estimating functional-group optical properties from a classical electrostatic atom dipole interaction model. In order to show extensively the efficiency of the classical model in reproducing the optoelectronic results of purely quantum calculations, it was used aggregates of butane, benzene, pyridazine, m-nitrophenol and p-nitrophenol, besides truly polymeric chains built from covalently connected building blocks. Herewith, the classical model proved to be efficient in several types of chemical environments, from the most weakly connected, such as those that present only dispersive interactions and also those strongly linked, as the case of covalent bonds.