A Novel Chromophore with a Large Two-Photon Absorption Cross-Section: 2,7-Bis[3-(4-N,N-dimethylaminophenyl)propenylidene]cyclohepta-3,5-dien-1-one

MASAHARU AKIBA, NAOKI MORINAGA, HIROO TAKIZAWA, MASASHI OGIYAMA, SEIJI ICHIJIMA, TAKEHARU TANI, AKINORI HARADA, and YOSHIO INAGAKI

A cross-conjugated cyclic ketone 2,7-Bis[3-(4-N,N- dimethylaminophenyl) propenylidene]cyclohepta-3,5-dien-1-one was prepared through condensation of 3-(4-N,N-dimethylaminophenyl) propenal and 4,5-dibromocycloheptanone followed by dehydrobromination. The two-photon absorption cross-section of this novel compound obtained in a chloroform solution by a fluorescence-based technique with Ti:sapphire laser at 890 nm was 4,330 GM. This value is 31 times as large as that of a closely related compound, 2,5-bis[3-(4-N,N-dimethylaminophenyl) propenylidene]cycloheptan-1-one, suggesting that the conjugated diene structure in the seven-membered ring plays a crucial role.