The role of aromatic π-bridges in push–pull-chromophores on the transparency-hyperpolarizability tradeoff

We present electronic structure calculations of the ultraviolet/visible (UV–Vis) spectra as well as hyperpolarizabilities (HP) of push–pull chromophores based on a donor-aromatic bridge-acceptor framework. As expected, both the color of the chromophores and the static hyperpolarizability are sensitive functions of modifications of the conjugated framework. Effects can be rationalized by determining zwitter-ionic mesomers of the bridge that can be stabilized by the donor or acceptor. The choice of bridge coupled with the substitution pattern on the ring allows targeting specific spectral features (absorption or transparency windows). Exceptionally large hyperpolarizabilities were found for the cyclopentadieno[1,2]-benz[4,5-b]cycloheptatriene bridge.