Nonlinear optical properties of push-pull stilbenes based on a strong carbocation acceptor moiety

Nonlinear optical properties of push-pull stilbenes based on an alkylamino donor and a strong carbocation acceptor moieties are analyzed in the presen t study. The highly electron-acceptor character of the carbocation group ma kes this kind of molecule promising material for second-order nonlinear opt ical applications. Photoinduced intramolecular charge-transfer is studied b y second harmonic generation in solution using time-resolved nondegenerate six-wave mixing. The fully characterized nonlinear dye Disperse Red 1 is us ed as a reference. The second-order nonlinear properties of the carbocation molecules are compared to a more standard amino-nitro push-pull stilbene. Kerr ellipsometry measurements aiming at a better understanding of the nonl inear excited state spectroscopy of the molecules are also reported. They r eveal a very short excited state lifetime of the molecules. Optimization of this lifetime should lead to an improvement of the six-wave mixing respons e of such compounds. (C) 1999 American Institute of Physics. [S0021-9606(99 )50240-7].