OPTICAL PROPERTIES PYRIMIDINE DERIVATIVES: EFFECT OF ELECTRON-DONOR/ACCEPTOR SUBSTITUENTS IN MOLECULAR TOPOLOGY

Abstract

In this work, we describe the synthetic approach of pyrimidine-substituted derivatives, photoluminescence properties and theoretical calculations of the geometry optimization and electron density distribution on the molecules in the ground and excited states. According to calculations, the location of HOMO electron density is mainly located over the molecular region with highest electron-donor character (or lower electron-acceptor). On the other hand, the electronic transition from HOMO to LUMO promotes a change in the electron density distribution on the molecule. The simulations also reveal that plane of all aryl substituent’s located at positions 2 and 6, are out of the pyrimidine ring plane and the absolute dihedral angles values between n-(p-phenyl) and pyrimidine ring planes are intrinsically dependent on the spatial HOMO distribution on the phenyl ring and p-substituent group. The higher donor character of the substituent leads to substantial changes in the absorption spectra. We also notice that the absorption changes are intrinsically related to the portion of ICT in the molecules, which are strongly dependent on polar interaction. All compounds present large Stokes shifts, higher than 3.370 cm^-1, and the emission spectra in solution present broad bands in the ultraviolet-visible region. On the other hand, the solid-state luminescence of 3a and 3c compounds shows emission band in the near-yellow color region 0.423, 0.475 (x, y) and 0.485, 0.542, respectively, in which the 5a and 5c compounds exhibit emission bands corresponding to the near-red color region 0.569, 0.415 and 0.608, 0.389, respectively.