Sabriye Acikgoz

FRET between BODIPY Azide Dye Clusters within PEG-Based Hydrogel: A Handle to Measure Stimuli Responsiveness

The purpose of this paper is to investigate the dynamics of the fluorescence mechanism of boradiazaindacene (BODIPY) dye molecules, which are covalently bound to a polyethylene glycol based hydrogel structure with different concentrations, using a picosecond time-resolved spectroscopic technique. Since the hydrogel structure is capable of absorbing a large amount of water, without dissolving and without losing its shape, upon swelling, the distance between the BODIPY azide dyes is controllably changed; it is observed that the intensity weighted fluorescence lifetime for the highly concentrated donor dye molecules embedded in the hydrogel cluster network changes from 2.03 to 7.14 ns. Calculations based on our experimental results suggest that the fluorescence dynamics of the BODIPY azide dye molecules confined within the hydrogel network obeys the Forster resonance energy transfer (FRET) rather than self (or contact) quenching. If the hydrogel is dry, in which the distance between donors and acceptors is minimum, the energy transfer efficiency is found to be about 72%, and the distance between the two dye molecules is calculated to be 4.59 nm. Such a close placement causes a significant reduction in the fluorescence intensity due to a strong dipole-dipole interaction of the dye molecules. As the separation increases upon hydrogel swelling, the FRET efficiency reduces to 2%, which corresponds to a separation of 10 nm between two BODIPY dyes and hence a considerable increase in the level of fluorescence intensity. For the dilute hydrogel samples, the distance between the dye molecules is larger than the critical Forster distance. Therefore, the energy transfer efficiency for this type of dilute samples is found to be much lower.

Investigation of the photoinduced electron injection processes for natural dye-sensitized solar cells: the impact of anchoring groups

In this study, nine different natural dyes having various anchoring groups were extracted from various plants and used as photo-sensitizers in DSSC applications. The photovoltaic parameters controlling the cell performance were investigated and the results were discussed as a function of anchoring groups. The obtained power conversion efficiencies (PCEs) vary from 0.18 to 1.87%, while the quantum yields are heavily dependent on both the anchoring group and type of pigments. Moreover, the effects of anchoring groups on the photoinduced electron injection dynamics from natural dye molecules to TiO2 nanoparticles were studied using time resolved fluorescence spectroscopy measurements. In these dyes, the long-hydroxyl & carbonyl-chain bearing anthocyanin, with the maximum electron transfer rate (kET), has shown the best photosensitization effect with regard to cell output. Despite the fact that their performance in DSSCs is somewhat lower or close to the metal complexes, these metal-free natural dyes can be treated as a new generation of sensitizers.

Monitoring excimer formation of perylene dye molecules within PMMA-based nanofiber via FLIM method

Confocal fluorescence lifetime imaging microscopy method is used to obtain individual fluorescence intensity and lifetime values of aromatic Perylene dye molecules encapsulated into PMMA based nanofibers. Fluorescence spectrum of aromatic hydrocarbon dye molecules, like perylene, depends on the concentration of dye molecules and these dye molecules display an excimeric emission band besides monomeric emission bands. Due to the dimension of a nanofiber is comparable to the monomer emission wavelength, the presence of nanofibers does not become effective on the decay rates of a single perylene molecule and its lifetime remains unchanged. When the concentration of perylene increases, molecular motion of the perylene molecule is restricted within nanofibers so that excimer emission arises from the partially overlapped conformation. As compared to free excimer emission of perylene, time-resolved experiments show that the fluorescence lifetime of excimer emission of perylene, which is encapsulated into NFs, gets shortened dramatically. Such a decrease in the lifetime is measured to be almost 50 percent, which indicates that the excimer emission of perylene molecules is more sensitive to change in the surrounding environment due to its longer wavelength. Fluorescence lifetime measurements are typically used to confirm the presence of excimers and to construct an excimer formation map of these dye molecules.

Decay rate measurement of perylene dye molecules attached to porous silicon nanostructures

The radiative decay rates of perylene dye molecules, attached to silicon nano-rods are investigated by means of timeresolved fluorescence experiments. The decay rates of dye molecules in the vicinity of silicon nano-rods are inhibited due to their various diameters and therefore the modification of the surrounding environment. Inhibition is caused by an increased nonradiative rate due to resonant energy transfer described by the Gersten-Nitzan model.