A series of thiophenes and bithiophenes containing combinations of dimethylamino and dimethylhydrazono π-donor and nitro and dicyanovinyl π-acceptor groups was synthesized in order to study their non-linear optical properties. Solution molecular hyperpolarizabilities were determined by a combination of experimental dipole moments and results from the electric field induced second harmonic generation experiment. Values obtained correlate well with those calculated by the CNDOVSB molecular orbital method. The main structure-property relationships deduced from the results are: (i) thiophene provides a more efficient electron delocalization pathway than benzene; (ii) this increase is proportionately even greater for bithiophene compared with biphenyl; (iii) dimethylhydrazono results in twice the hyperpolarizability of dimethylamino in a comparable molecule; and (iv) dicyanovinyl is a more effective electron acceptor group than nitro in the thiophenes synthesized and calculated.