Browsing by Subject "White light emission"

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    ItemOpen Access
    Synthesis and characterizations of conjugated oligomers and nanoparticles for optoelectronic and biological applications
    (2016-08) Köken, Emre
    This project firstly aims to develop water dispersible conjugated nanoparticles by reprecipitation method for FRET based white light emission. Preliminary NPs study with only OFT Pgy and only OFVBt N3 were done in order to determine size and distribution of NPs. Overlapping optical properties of donor (OFT Pgy) and acceptor (OFVBt N3) give possibility to FRET applications. By click reaction in water, terminal sites of oligomers are connected and white emission is sealed by keeping D-A pair close. FRET based white light is widely used in optoelectronic applications such as OLEDs or more specifically WOLEDs. Since the white light covers all visible spectrum, different color emissions are obtainable depending on excitation wavelength. Various biosensor and bioimaging applications are also possible with white light emitting NPs, since they are readily and stably dispersed in water. In second part of the project, OFVBt N3 oligomer is cross-linked with di-sulfide containing crosslinker via copper catalyzed click reaction. NPs were synthesized in THF to obtain high click efficiency and redispersed in water, since the biological applications are targeted. OFVBt N3 oligomer is advantageous for bioimaging with its red emission close to IR region, since lower frequency emission overcomes the background auto-fluorescence and penetrates deeper in the body. Di-sulfide crosslinker, in addition to connecting the oligomer molecules and stabilizing NPs, provides possibility of drug delivery application. Since GSH (glutathione) or Trx (thioredoxin) like thiol bearing bio-molecules subsist in higher concentrations in tumorous tissues, di-sulfide bond can be cleaved, releasing the loaded drug from NPs. Thus, crosslinked OFVBt N3 NPs is a theranostic agent with an advantageous emission color for bio-imaging and a cleavable di-sulfide bond for drug delivery & controlled release. In last part of the study, white light emitting bi-oligomer nanoparticles were designed and obtained by using OFB Pgy and Porph N3. A quality white emission requires to cover all visible spectrum and overlapping optical properties of OFB Pgy (D) and Porph N3 (A) is used to white light emission by FRET. The purpose of clicking the oligomer pair is to stabilize the FRET efficiency. Moreover, using THF as the solvent is not only facilitated a better click chemistry, but also provided ease of applicability for solid state white light applications. Since THF evaporates easily, white light emitting NPs can form film on various surfaces. Thus, these NPs requires no host layer and can be applied directly to electrode surface when optoelectronic applications e.g. OLEDs or WOLEDs are considered.
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    ItemOpen Access
    White-emitting conjugated polymer nanoparticles with cross-linked shell for mechanical stability and controllable photometric properties in color-conversion LED applications
    (2011) Park, Eun-Ju; Erdem, T.; Ibrahimova, V.; Nizamoglu, S.; Demir, Hilmi Volkan; Tuncel, D.
    We report on the synthesis and characterization of water-dispersible, mechanically stable conjugated polymer nanoparticles (CPNs) in shelled architecture with tunable emission and controllable photometric properties via cross-linking. Using a reprecipitation method, whiteemitting polymer nanoparticles are prepared in different sizes by varying the concentration of polymer; the emission kinetics are tuned by controlling the shell formation. For this purpose, polyfluorene derivatives containing azide groups are selected that can be decomposed under UV light to generate very reactive species, which opportunely facilitate the inter- and intra-cross-linking of polymer chains to form shells. Nanoparticles before and after UV treatment are characterized by various techniques. Their size and morphologies are determined by using dynamic light scattering (DLS) measurements and imaging techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM). For optical characterization, UV vis and steady-state and timeresolved fluorescent spectroscopies are performed. Solid-state behaviors of these CPNs are also investigated by forming films through drop-casting. Moreover, the photometric calculations are also performed for films and dispersions to determine the color quality. A device has been constructed to show proof-of-principle white light generation from these nanoparticles. Additionally, mechanical stability studies are performed and demonstrated that these nanoparticles are indeed mechanically stable by removing the solvent after cross-linking using a freeze-dryer and redispersing in water and THF. Optical and imaging data confirm that the redispersed particles preserve their shapes and sizes after cross-linking.