Abstract
AM1 calculations are performed to study the non-linear optical properties of push–pull polyenes. On adopting different donor and acceptor groups in hexatriene a set of hexatriene derivatives is obtained whose bond length alternations (BLA) are calculated to be −0.070 to 0.110 Å, ranging from a charge-separated form to a neutral polyene form. Another parameter, δDA′ is also introduced to characterize the effectiveness of donor–acceptor pairs. The relationships between the polarizabilities and δDA′ or BLA are investigated, giving an insight into the electronic origin of the linear and non-linear responses of these donor–acceptor substituted polyene molecules. The results may provide structural guides on selecting donor and acceptor groups for synthesizing molecules with desired non-linear optical (NLO) properties.