Browsing by Subject "Fluorescence spectroscopy"
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Item Open Access Convergent synthesis and light harvesting properties of dendritic boradiazaindacene (BODIPY) appended perylenediimide dyes(2010) Bozdemir, O. A.; Yilmaz, M. D.; Buyukcakir, O.; Siemiarczuk, A.; Tutas, M.; Akkaya, E. U.A convergent synthesis methodology, together with "click- chemistry" between azides and terminal alkynes, allows straighforward access to dendritic light harvesting systems. The novel dendrimer reported in this study has eight boradiazaindacene (BODIPY) units at the periphery and a perylenediimide (PDI) dye at the core. We have demonstrated that visible light is effectively collected as a result of the large absorption cross section of the dendrimer and efficiently channeled to the core PDI unit, resulting in a significant antenna effect. While being one of the very few energy transfer systems with a BODIPY and PDI chromophore pair, this novel dendritic molecule is one of the most efficient in light harvesting. The factors that may play important roles as the generation number increases also become apparent when emission characteristics were analyzed in comparison with a lower generation dendrimer.Item Open Access Dispersion of multi-walled carbon nanotubes in an aqueous medium by water-dispersible conjugated polymer nanoparticles(2010) Baykal, B.; Ibrahimova, V.; Er, G.; Bengü, E.; Tuncel, D.Vertically aligned multi-walled carbon nanotubes (MWCNTs) synthesized by the alcohol catalytic CVD (ACCVD) technique are dispersed in water with the aid of water-dispersible conjugated polymer nanoparticles (CPNs). The interactions between CPNs and CNTs are studied with spectroscopy (UV-Vis, fluorescence and Raman) and electron microscopy techniques are used to confirm attachment of CPNs to the CNT sidewalls.Item Open Access Synthesis of symmetrical multichromophoric bodipy dyes and their facile transformation into energy transfer cassettes(2010) Bozdemir, O. A.; Cakmak, Y.; Sozmen F.; Ozdemir, T.; Siemiarczuk, A.; Akkaya, E. U.Multichromophoric boron-dipyrromethene (Bodipy) dyes synthesized on phenylene-ethynylene platforms have been be converted to energy transfer cassettes in a one-step chemical transformation. Excitation energy transfer processes in these highly symmetrical derivatives were studied in detail, including time-re-solved fluorescence spectroscopy techniques. Excitation spectra and the emission lifetimes suggest efficient energy transfer between the donor and acceptor chromophore. These novel energy transfer cassettes, while highlighting a short-cut approach to similar energy transfer systems, could be useful as large pseudo-Stokes shift multichromophoric dyes with potential applications in diverse applications.Item Open Access Type-II colloidal quantum wells: CdSe/CdTe core/crown heteronanoplatelets(American Chemical Society, 2015) Keleştemur, Y.; Olutas M.; Delikanlı, S.; Güzeltürk, B.; Akgül, M. Z.; Demir, Hilmi VolkanSolution-processed quantum wells, also known as colloidal nanoplatelets (NPLs), are emerging as promising materials for colloidal optoelectronics. In this work, we report the synthesis and characterization of CdSe/CdTe core/crown NPLs exhibiting a Type-II electronic structure and Type-II speci fic optical properties. Here, based on a core-seeded approach, the CdSe/CdTe core/crown NPLs were synthesized with well-controlled CdTe crown coatings. Uniform and epitaxial growth of CdTe crown region was verified by using structural characterization techniques including transmission electron microscopy (TEM) with quantitative EDX analysis and X-ray diffraction (XRD). Also the optical properties were systematically studied in these Type-II NPLs that reveal strongly red-shifted photoluminescence (up to ∼150 nm) along with 2 orders of magnitude longer fluorescence lifetimes (up to 190 ns) compared to the Type-I NPLs owing to spatially indirect excitons at the Type-II interface between the CdSe core and the CdTe crown regions. Photoluminescence excitation spectroscopy confirms that this strongly red-shifted emission actually arises from the CdSe/CdTe NPLs. In addition, temperature-dependent time-resolved fluorescence spectroscopy was performed to reveal the temperature-dependent fluorescence decay kinetics of the Type-II NPLs exhibiting interesting behavior. Also, water-soluble Type-II NPLs were achieved via ligand exchange of the CdSe/CdTe core/crown NPLs by using 3-mercaptopropionic acid (MPA), which allows for enhanced charge extraction efficiency owing to their shorter chain length and enables high quality film formation by layer-by-layer (LBL) assembly. With all of these appealing properties, the CdSe/CdTe core/crown heterostructures having Type-II electronic structure presented here are highly promising for light-harvesting applications. (Graph Presented). © 2015 American Chemical Society.