The Study Of Fluorescent Semiconductor Nanoparticles-Organic Dye Composites With Strong Two-Photon Absorption Effect

Organic materials with large two-photon absorption (TPA) cross sections are currently under considerable investigation for applications such as 3D microfabrication, two-photon upconversion lasing, optical power limiting, two-photon fluorescence microscopy, and three-dimensional optical data storage. However, the early development of TPA-based application was limited because the available materials had relatively small TPA cross-sections. So the study of material with large TPA cross section is one of our targets. Organic compounds with large two-photon absorption cross-sections have been extensively studied, it is also known that monodisperse semiconductor cluster belonging to II-IV group with a sharp exciton absorption band contribute to the enhancement of nonlinear optical response due in part to large local field effect. Therefore, the basic idea of my thesis is to study the two-photon absorption properties of composite systems of semiconductor nanocrystals (NCs) and organic two-photon chromophores.Two multibranched organic ligands l,2,4,5-tetrakis(4-pyridylvinyl)benzene (TKPVB) and l,2,4,5-Tetrakis(4-N-methyl-Nhydroxyethylamino)vinylphenylbenzene (TKAVPB) with strong TPA effect were synthesized by an efficient solvent-less Wittig-Horner reaction. The TPA cross sections of the two compounds were measured with the two-photon-induced fluorescence method by using femtosecond Ti-sapphire laser pulses. The single-photon fluorescence of the two compounds in different polar solvents was studied and red shift of spectra with increasing the polarity of the solvents was observed. Such phenomenon can be explained by the TICT (twisted internal charge transfer) model as reported in the references. The single-photon fluorescence and two-photon fluorescence spectra of TKPVB in neural, basic and acidic solutions were explored. In acidic solution, TKPVB exists as amine salt. The replacement of stronger electron withdrawing group decreases the polarity of excited states and increases the extent of charge transfer, so the red shift of the...