Kinetics and mechanism of donor-acceptor azulenic optical limiting molecules

The transient absorption spectra and kinetics of ten new donor-acceptor azu lenic molecules, after excitation of the charge-transfer band, have been st udied by means of ultrafast transient spectroscopy. All of the molecules sh ow intense and broad reverse saturable absorption bands in the visible regi on, which appear within the excitation pulse (tau = 1 ps), and decay with p icosecond lifetimes. The early time steps of the photochemical mechanism of these azulenes are proposed. Owing to the high absorption cross-section, f ast kinetics and broad spectral response, these molecules may serve as the active media for optical limiting devices. (C) 2000 Elsevier Science B.V. A ll rights reserved.