Design, synthesis, characterization and applications of multi-photon absorbing chromophores
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Recent development in multi-photon based applications including optical power limiting, frequency up-conversion lasing, three-dimensional data storage, two-photon fluorescence microscopy and two-photon photodynamic therapy has benefited a lot from a number of chromophores with large multi-photon absorption. This thesis was focused on the development of novel two- and three-photon active chromophores and their applications. Chapter 1 describes a theoretical background of multi-photon absorption, and recent development of multi-photon based applications. Some molecular design strategies were proposed after a literature review of chromophores with large two-photon absorption. In Chapter 2, a series of stilbazolium salts with varying electron donors and anions were synthesized and characterized. The two-photon absorption and two-photon pumped cavity lasing properties for these dyes were studied by using 1064 nm nano-second laser beam. By using tunable femto-second laser, three-photon pumped cavity-less lasing properties of these dyes have also been comprehensively studied. Four-photon pumped stimulated emission was achieved in some of these stilbazolium dyes. Unsymmetrical emission behaviors under 3- and 4-photon pump conditions for all these stilbazolium dyes were observed, explained and verified. In Chapter 3, DNA was successfully used as a matrix for one-, two-, and three-photon pumped stimulated emission or lasing by intercalating a multi-photon active chromophore. In Chapter 4, it is experimentally shown that both two- and three-photon absorption in a highly concentrated chromophore system can be more efficiently utilized to accomplish optical power limiting and stabilization at laser wavelengths of 1.064 μm and ∼1.3 μm, respectively. In Chapter 5, three novel 1,10-phenanthroline containing π-conjugated chromophores with varied electron donors were synthesized and characterized together with their corresponding nickel(II) chelated complexes. Large two-photon absorption with quenched emission was found for the nickel(II) chelated complexes. In Chapter 6, a novel π-conjugated dendritic nano-sized chromophore, was synthesized and characterized, together with its corresponding one- and three-branched units. Two- and three-photon absorption, two- and three-photon excited emission properties, and thermal stabilities for these compounds were comprehensively studied.