γ-Methylene chalcogenapyrans and benzopyrans as proaromatic donors in “push–pull” Fischer type carbene complexes: Influences of chalcogen atom and chain length on the electronic and N.L.O. properties of these molecules

A new class of push–pull molecules bearing γ-methylene chalcogenapyran and benzopyran nucleus as proaromatic donors and methoxypentacarbonyltungstene carbene fragment as acceptors is described. N.L.O. properties (as μβ by EFISH) of these complexes have been investigated. The influence of the unsaturated chain length, of the presence of the fused aromatic ring and of the chalcogen atom on the first hyperpolarizability values are shown.