Nonlinear multiphoton processes in organic and [organic:inorganic] hybrid materials: Design, synthesis and characterization

For the past decade, the nonlinear optical effect in organic system has drawn a great deal of attention because it provides the flexibility to tailor its structures at molecular level and to optimize their nonlinear optical response.; Chapter 1 describes a brief introduction of the nonlinear multiphoton process. This includes theoretical origin of multiphoton process, research efforts to establish design criteria for development of better molecular structure and some practical applications.; Chapter 2 reports discovery of cooperative enhancement of two-photon absorption in multibranched structures, which may lead to new design criteria for development of efficient two-photon materials. The two-photon cross-sections measured both with nanosecond and femtosecond pulses show that the value for the trimer is more than six times larger than that for the monomer.; In Chapter 3, the erbium cored two-photon dye complex [Er 3+:PRL-101A] was prepared and optical properties of this two-photon dye complex were investigated. It is observed that the photoluminescence (fluorescence) of the two-photon dye complex was quenched significantly while nonlinear absorption for infrared nanosecond excitation was enhanced compared to the two-photon dye (PRL-101A). Analysis of the nonlinear absorption (power limiting) data suggests that the intersystem crossing rate be 3 orders of magnitude larger for the erbium two-photon dye complex [Er3+:PRL-101A ] compared with that two-photon dye (PRL-101A).; In Chapter 4, a new multibranched two-photon absorbing structure ET-101 which contains a two-dimensional molecular architecture with four arms and one bridging unit was constructed. Each of these segments has an extended π-conjugation and is capable of producing two-photon absorption in different spectral range. The linear absorption and luminescence spectra of the components and the multibranched structure revealed a very effective energy transfer from the excited arm units to the π-conjugated bridging unit.; Chapter 5 reports the preparation and luminescence properties of a novel [zinc sulfide (core)]-[two-photon dye]-[silica (shell)] multilayered nanoparticle. The method utilizes reverse micelles synthesis. The nanoparticles with different sizes and morphologies could be obtained. The size of these composite particles is typically 15∼30 nm. An increase in the luminescence intensity (∼70 times higher) and in fluorescence lifetime is observed for the multilayered nanoparticle compared with the free dye. (Abstract shortened by UMI.)...