Browsing by Subject "light harvesting"

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Exciton harvesting systems of nanocrystals
(2011) Mutlugün, Evren
Semiconductor nanocrystals, also known as colloidal quantum dots, have gained substantial scientific interest for innovative light harvesting applications including those in biolabeling. Organic dyes and fluorescent proteins are widely used in biotargeting and live cell imaging, but their intrinsic optical properties, such as narrow excitation windows, limit their potential for advanced applications, e.g., spectral multiplexing. Compared to these organic fluorophores, favorable properties of the quantum dots including high photoluminescence quantum yields together with tunable emission peaks and narrow spectral emission widths, high extinction coefficients, and broad absorption bands enable us to discover and innovate light harvesting composites. In such systems, however, the scientific challenge is to achieve high levels of energy transfer from one species to the other, with additional features of versatility and tunability. To address these problems, as a conceptual advancement, this thesis proposes and demonstrates a new class of versatile light harvesting systems of semiconductor nanocrystals mediated by excitonic interactions based on Förstertype nonradiative energy transfer. In this thesis, we synthesized near-unity efficiency colloidal quantum dots with as-synthesized photoluminescence quantum yields of >95%. As proof-of-concept demonstrations, we studied and achieved highly efficient exciton harvesting systems of quantum dots bound to fluorescent proteins, where the excitons are zipped from the dots to the proteins in the composite. This led to many folds of light harvesting (tunable up to 15 times) in the case of the green fluorescent protein. Using organic dye molecules electrostatically interacting with quantum dots, we showed high levels of exciton migration from the dots to the molecules (up to 94%). Furthermore, we demonstrated stand-alone, flexible membranes of nanocrystals in unprecedentedly large areas (> 50 cm × 50 cm), which paves the way for highend, large-scale applications. In the thesis, we also developed exciton-exciton coupling models to support the experimental results. This thesis opens up new possibilities for exciton-harvesting in biolabeling and optoelectronics.
Open Access
Light harvesting and efficient energy transfer in boron dipyrrin dyads and derivatization for potential utility in dye-sensitized solar cells
(2008) Barın, Gökhan
In bichromophoric supramolecular systems light is harvested by antenna components and excitation energy is channeled into an acceptor component. We have designed and synthesized novel energy transfer cassettes which are based on boradiazaindacene (BODIPY) units. Facile synthesis of long wavelength absorbing distyryl BODIPY dyes has been applied successfully in this study. In the first part of the thesis, efficient energy transfer from energy donor BODIPYs to long wavelength absorbing distyryl BODIPY core was demonstrated. To observe the antenna effect quantitatively, we have designed the cassettes with an increasing number of energy donor components. Based on these observations, in the second part of the thesis, we have introduced a light-harvesting photosensitizer for dye-sensitized solar cell (DSSC) purposes. The target molecule absorbs in visible and near-IR region and energy transfer is demonstrated successfully. Our design appears to be highly promising for DSSC.
Open Access
Non-covalently functionalized SWNTs as potential delivery agents for novel BODIPY*based PDT sensitizers & the design and synthesis of dendritic light harvesters
(2009) Erbaş, Sündüs
Photodynamic therapy (PDT) is a non-invasive method used for the treatment of a number of diseases including certain cancers and some cardiovascular diseases. Photodynamic action depends on absorbance of photosensitizer (PS) in near IR region of the spectrum and subsequent generation of cytotoxic singlet oxygen in the vicinity of the PS. Carbon nanotubes are widely used for biomedical applications due to their inertness, biocompatibility, cellular internalization, facile and multi-modification. We have synthesized and characterized novel water soluble boradiazaindacene (BODIPY)-based PS, noncovalently attached on to the single wall carbon nanotube (SWNT). We have observed that near infrared absorbing photosensitizer preserve its singlet oxygen generation capability upon adsorption on SWNT. We have demonstrated that SWNTs can be used as the delivery vehicle of PS for the use in PDT. In the second part of this research, multichromatic cascade-type light harvesting BODIPY dendrimers were synthesized and highly efficient energy transfer was observed. Successful channeling of energy in a predefined region of the dendrimer was revealed.
Open Access
Rational design and synthesis of bodipy dyes for molecular sensing, light harvesting and photodynamic applications
(2014) Kütük, Tuğba Özdemir
BODIPY dyes have been addressed in many applications due to highly important features. These unique properties can be summarized as high photostability, high extinction coefficient, easy functionality, etc. Thus, tremendous studies have been published and, ion sensing, photodynamic therapy, dye-sensitized solar cells and light harvesting are some of the areas that BODIPY dyes have been utilized. In this thesis, BODIPY dyes were functionalized to be used for different concepts. In the first study, the main purpose was to seek for ion signaling differences of two isomeric tetra-styryl BODIPY dyes with charge donor ligand located at 1,7 versus 3,5 positions. Second work focuses on the light harvesting concept with the use of tetra-styryl BODIPY derivatives. Third study describes the coupling of energy transfer with internal charge transfer to monitor the alterations in intensity ratios, so, dynamic range of the fluorescent probe is improved. Design and synthesis of BODIPY dyes for detection of biological thiols in aqueous solution both chromogenically and fluorogenically was given in fourth study. Another biologically important molecule, hydrogen sulfide is selectively detected via BODIPY-based probe and depicted in the fifth study. In the sixth work, persistent luminescent nanoparticles are attached to BODIPY-based photosensitizer to activate the photodynamic action.