Symmetrical and Unsymmetrical 4,7-Bis-arylvinyl-benzo-2,1,3-chalcogenodiazoles: Synthesis, Photophysical and Electrochemical Properties and Biomolecular Interaction Studies: Symmetrical and Unsymmetrical 4,7-Bis-arylvinyl-benzo-2,1,3-chalcogenodiazoles: Synthesis, Photophysical and Electrochemical Properties and Biomolecul