Browsing by Author "Bhongale, CJ"

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Emission enhancement by formation of aggregates in hybrid chromophoric surfactant amphiphile/silica nanocomposites
(2006)
Bhongale, CJ
;
Hsu, CS
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應用化學系
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Department of Applied Chemistry
Formation of nanostructures of hexaphenylsilole with enhanced color-tunable emissions
(2006-02-26)
Bhongale, CJ
;
Chang, CW
;
Diau, EWG
;
Hsu, CS
;
Dong, YQ
Nanostructures of 1,1,2,3,4,5-hexaphenylsilole (HPS) of various types were obtained on simple reprecipitation with THF as solvent and water as non-solvent. The formation and evolution of these nanostructures were monitored with scanning electron microscopy. Using picosecond time-correlated single-photon counting, we observed enhanced emission and fluorescence lifetimes at volume fractions 70-90% of added water. We report the first enhanced color-tunable emissions of a conjugated organic compound (HPS) due to the formation of nanoflowers, nanoglobules and microglobules, and provide time scales for those nanostructures and the corresponding intermolecular interactions in the aggregates. (c) 2005 Elsevier B.V. All rights reserved.
Relaxation dynamics and structural characterization of organic nanoparticles with enhanced emission
(2005-07-21)
Bhongale, CJ
;
Chang, CW
;
Lee, CS
;
Diau, EWG
;
Hsu, CS
With a reprecipitation method, we prepared fluorescent organic nanoparticles of 1,4-di[(E)-2-phenyl-1-propenyl]-benzene (PPB) that feature weak emission in solution but exhibit blue-shifted absorption and strong emission as aggregates. Picosecond fluorescent transients of these PPB nanoparticles showed biexponential decay, described with a consecutive kinetic model involving two emissive states. X-ray diffraction patterns of PPB nanocrystals indicate long-range packing structures of two types, one the same as in a single crystal and the other not yet determined. PPB molecules in a crystal show an arrangement of a herringbone type with three benzene rings in a PPB unit being nearly planar and two methyl groups of the unit pointing along the same direction, in contrast to the twisted structure of an isolated PPB molecule. Fluorescence transients of PPB on a femtosecond scale indicate an efficient channel for isomerization that is activated for free PPB in solution but inhibited in PPB forming nanoparticles, demonstrating the significance of molecular geometry and twisting motions that affect the relaxation dynamics in the excited state. The versatile techniques combined in this work provide strong evidence to improve our understanding of optical properties in organic nanoparticles dependent on size.