Nonlinear optical chromophores containing dithienothiophene as a new type of electron relay

Nonlinear optical (NLO) donor-acceptor (D-A) chromophores containing a fused terthiophene, namely dithienothiophene (DTT) as electron relay, and various strength acceptors were synthesized to evaluate the relay's role in the solvatochromism as well as in the molecular nonlinearity, µβ(0). Their solvatochromic behavior, which is dependent on acceptor strength, is correlated to their µβ(0). The static quadratic hyperpolarizability, β(0), of DTT-containing chromophores was determined by EFISH measurements. From the comparison of µβ(0) values of D-A chromophores based on oligothiophenes, it was assessed that DTT as relay is significantly more efficient compared to bithiophene (the same number of conjugated double bonds) and terthiophene. An additional merit of DTT is that chromophores containing DTT have a noticeably high thermal stability.