New dendrimer molecules with a record high intrinsic two-photon absorption cross-section

Summary form only given. Two-photon absorption (TPA) is a third-order nonlinear optical process, in which two photons are absorbed simultaneously such that the energy of the photons adds up to the energy of the molecule´s excited state. TPA has important applications in three-dimensional optical data storage, photolithography, scanning fluorescence microscopy, optical power limiting, etc. These applications exploit the fact that the rate of TPA has a quadratic dependence on the illuminating laser intensity. In particular, TPA allows confining absorption to a small diffraction-limited volume. This effect has been used recently for micro-fabrication of photonic band gap materials, tapered optical wave-guides and micro-electromechanical devices. A majority of known organic molecules have a very small nonlinear absorption cross-section, typically /spl sigma//sub 2//spl sim/1 GM (1 GM=10/sup -50/ cm/sup 4/s photon/sup -1/ molecule/sup -1/), which is insufficient for most proposed applications. An increase in /spl sigma//sub 2/ value has been achieved by using molecular design elements such as extension of /spl pi/-conjugation length of the molecule and by introduction of electron-donating (D) and electron-accepting (A) groups at the opposite ends of a linear molecule. In this paper we present results on measurement of two-photon absorption properties of a new class of macro-molecules with even higher intrinsic /spl sigma//sub 2/. These molecules are synthesized by using a strong D-A-D type two-photon absorbing chromophore 4,4´-bis(diphenylamino)stilbene as a building block for a much larger nanometer-size dendrimer structure.