Nonlinear Optical Chromophores Containing Fused Terthiophene As A New Type of Electron Relay

Thiophene-based D-A molecules have been actively sought recently, exploiting interesting results indicating that the incorporation of a thiophene unit or the replacement of a phenylene moiety by thienylene in the relay of a D-A molecule enhanced the molecular hyperpolarizability (μβ(0)) significantly (1-3). Accordingly, it is expected that oligothiophenes give a larger contribution to the μβ(0) compared to oligophenylenes. As in the case of polyenes, the rigidification of thiophenes (by cyclization) has also been known to enhance charge-transfer in push-pull D-A molecules, as indicated by a bathochromic shift of absorption bands and a stronger solvatochromism compared to the flexible counterpart (4,5). A further indication for the effectiveness of fused thiophenes as relay is demonstrated by the fact that their absorption maxima increase linearly with the number of rings up to five (6). Aside from the electronic features, another merit of thiophenes is their inherent thermal stability from which thiophene-containing chromophores will benefit (2,3).