Synthesis of Hydrophilic Two-Photon Absorptive Fullerene-diphenylaminoflourene Dyads for Molecular Self-assembly in Wate
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Synthesis of Hydrophilic Two-Photon Absorptive Fullerene-diphenylaminoflourene Dyads for Molecular Self-assembly in Water Sarika Verma1; Tanya Hauck2; Prashant A.Padmawar1; Taizoon Canteenwala1; Long Y.Chiang1 and Kenneth P.H.Pritzker2 1 Department of Chemistry, Institute of Nanoscience and Engineering, University of Massachusetts, Lowell, MA 01854, U.S.A. 2 Pathology and Laboratory Medicine, Mount Sinai Hospital and University of Toronto, Toronto, ON M5G1X5, Canada. ABSTRACT Synthetic conditions for the preparation of amphiphilic two-photon absorptive poly(ethylene glycolated) diphenylaminofluorene[60]fullerene conjugates C60(>DPAF-PEG6) were investigated. UV-vis spectra of C60(>DPAF-PEG6) collected at the concentration of 1.0 x10−5 M in water showed absorption bands with a slight red shift, broadened, and in a less intensity as compared with those of the bands obtained in CHCl3. These features are important characteristics of C60(>DPAF-PEG6) molecular aggregation in water. Transmission electron micrographs taken at the concentration of 1.0 x10− 5 M in H2O clearly displayed images of spherical aggregates in a diameter of 200−400 nm. That substantiated high hydrophobic intermolecular interactions between these amphiphilic molecules for assemblies in water. INTRODUCTION A wide range of electronically conducting, magnetic, photochemical, and electrical features of C60 derivatives make them suitable optoelectronic materials for practical applications [1, 2]. Considering the unique high electron accepting ability of [60]fullerene, a large variety of donorlinked fullerene conjugates have been designed, synthesized, and studied for their photoinduced electron- and energy-transfer processes [3−5]. These processes make possible myriad of potential uses in photophysical and biomedical areas. Over the past decade, two-photon absorption (TPA) phenomena of organic chromophore molecules have attracted a considerable attention due to related promising applications, such as fluorescence imaging, data storage, microfabrication and photodynamic therapy. A number of chromophores including diphenylaminofluorene (DPAF) derivatives were investigated for the structural relationship to their multi-photon absorptivity. Relatively high TPA cross-sections were demonstrated on some branched DPAF-derived chromophores by covalent linking with different π-acceptors in a conjugate structure [6, 7]. Utility of diphenylaminofluorene subunit in the design of new chromophores is reasoned for its inherently high thermal and photochemical stability and easy functionalization at 2-, 7-, and/or 9carbon positions. Taking on similar approaches, our group reported the first highly TPA-active diethylated C60-DPAF derivative possessing a one-dimensional A-sp3-D molecular linkage with a close coupling of the electron accepting (A) fullerene cage and the electron donating (D) diphenylaminofluorene moiety. Accordingly, C60-DPAF dyads 7-(1,2-dihydro-1,2methano[60]fullerene-61-carbonyl)-9,9-diethyl-2-diphenylaminofluorene [C60(>DPAF-C2)] exhibits large
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