Electronic structure of two conjugated polymers, PPV and its derivative DIOXA-PPV, are studied by quantum-chemistry methods. Good agreement between the calculations and available experimental data validates the applied methods and enables us to draw conclusions about properties of excitons and polarons in these polymers. In particular, simultaneous use of different correlation plots in atomic site representation and transition densities in real space representation reveals electronic structure and spatial localization of the elementary excitations. The properties of the DIOXA-PPV are discussed in context of possible applications in molecular electronics devices.