Molecular design of organic nonlinear optics:: dipole moment, polarizability and hyperpolarizabilities of thiadiazole oligomers investigated by density functional theory methods

Several potentially conducting polymers, optically nonlinear polymers, and biomaterials contain heterocyclic structures. Reduction of the energy band gap of a conjugated polymer is a topic of considerable interest due to the possible elimination of doping in the preparation of highly conductive polymers. Control of the energy gap value of a polymer by molecular design could modify its optical, electronic and optoelectronic properties. Thiadiazoles and their derivatives are the structural basis of some of these polymeric materials. The results of the calculation of the HOMO-LUMO gap, the dipole moment and polarizability of thiadiazole oligomers in vacuo and in the presence of solvents are reported. The calculations are based on density functional theory using a specially tailored model chemistry. The potential utility of these materials for the development of chemical sensors is discussed.