Kinetics and mechanism of donor–acceptor azulenic optical limiting molecules

The transient absorption spectra and kinetics of ten new donor–acceptor azulenic molecules, after excitation of the charge-transfer band, have been studied by means of ultrafast transient spectroscopy. All of the molecules show intense and broad reverse saturable absorption bands in the visible region, which appear within the excitation pulse (τ=1 ps), and decay with picosecond lifetimes. The early time steps of the photochemical mechanism of these azulenes are proposed. Owing to the high absorption cross-section, fast kinetics and broad spectral response, these molecules may serve as the active media for optical limiting devices.