In this work, we present a comparative study of the second order nonlinear optical properties of a series of chromophores containing a fused terthiophene, namely dithienothiophene (DTT), as electron relay with either D-π-A or D-π-D substitution patterns. The effect of the acceptor/donor strength and the solvent polarity confirm the possibility of fine-tuning optical non-linearities in the asymmetric samples. The geometrical and electronic properties calculated in solution reveal that push-pull chromophores become highly polarized as the dielectric constant of the solvent increases. Theoretical NLO calculations furthermore reveal a moderate nonlinear optical activity for the symmetric samples.