Design and synthesis of donor-acceptor pyrazabole derivatives for multiphoton absorption.

A series of ferrocenyl substituted pyrazaboles were prepared, which have an electron-withdrawing pyrazabole moiety as the central core, with a D-π-A-π-D structural motif (D = donor, A = acceptor) and containing a variety of π bridges. A crystallographic study reveals that the pyrazabole central core was observed in planar geometry. Strong two-photon absorption in the visible region and three-photon absorption in the near IR region were observed in the ferrocenyl substituted pyrazaboles. It was observed that the 2PA absorption cross-section increases with the conjugation length.