Synthesis and NLO properties of 4-(4H-chalcogenopyran-4-ylidene and 4H-chalcogenochromen-4-ylidene)-1-(phenylthio)but-2-enylidene complexes - Electronic influence of the carbene fragment

The synthesis of 4-(4H-chalcogenopyran-4-ylidene and 4H-chalcogenochromen-4-ylidene)-1-(phenylthio)but-2-enyl-idene complexes is described and their non-linear optical (NLO) properties have been investigated (as mu beta by EFISH). NMR studies and X-ray crystallographic analyses show that the (phenylthio)carbene fragment has a better electron-withdrawing capability than the methoxy analogues and, likewise, the corresponding thiocarbenes have a more significant pyrylium character. The mu beta values of these complexes were obtained from EFISH experiments. The microscopic NLO response is sensitive to the nature of the intracyclic chalcogen atom, the nature of the metal centre and the benzo-annulation of the heterocycle.