Browsing by Author "Dede, Y."

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Open Access
Control of triboelectric charges on common polymers by photoexcitation of organic dyes
(Nature Publishing Group, 2019-01) Cezan, S. Doruk; Nalbant, Atakan A.; Büyüktemiz, M.; Dede, Y.; Baytekin, H. Tarık; Baytekin, Bilge
Triboelectric charging of insulators, also known as contact charging in which electrical charges develop on surfaces upon contact, is a significant problem that is especially critical for various industries such as polymers, pharmaceuticals, electronics, and space. Several methods of tribocharge mitigation exist in practice; however, none can reach the practicality of using light in the process. Here we show a light-controlled manipulation of triboelectric charges on common polymers, in which the tribocharges are mitigated upon illumination with appropriate wavelengths of light in presence of a mediator organic dye. Our method provides spatial and temporal control of mitigation of static charges on common polymer surfaces by a mechanism that involves photoexcitation of organic dyes, which also allows additional control using wavelength. This control over charge mitigation provides a way to manipulate macroscopic objects by tribocharging followed by light-controlled discharging.
Open Access
Corrigendum: Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation
(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-09-20) Ghobadi, T. Gamze Ulusoy; Ghobadi, Amir; Demirtaş, Merve; Büyüktemiz, M.; Kübra N., Özvural; Yıldız, E. A.; Erdem, E.; Yağlıgül, H. G.; Durgun, Engin; Dede, Y.; Özbay, Ekmel; Karadaş, Ferdi
The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications.
Open Access
Design and characterization of Bodipy derivatives for bulk heterojunction solar cells
(Elsevier, 2014) Kolemen, S.; Cakmak, Y.; Ozdemir, T.; Erten Ela, S.; Buyuktemiz, M.; Dede, Y.; Akkaya, E. U.
Two electron rich Bodipy dyes with strong absorptivities in the visible region were designed and synthesized as potential electron donors in bulk heterojunction photovoltaic constructs. Overall efficiency is above 1%, with impressive responsiveness at both UV and near-IR ends of the visible spectrum. Computational studies reveal an unexpected effect of meso-substituents on the electron transfer efficiency.
Open Access
Design and synthesis of soluble dibenzosuberane-substituted fullerene derivatives for bulk-heterojunction polymer solar cells
(2014) Kolemen, S.; Cakmak, Y.; Ozdemir, T.; Erten Ela, S.; Buyuktemiz, M.; Dede, Y.; Akkaya, E. U.
Two new dibenzosuberane-substituted fullerene derivatives, dibenzosuberane-C60 monoadduct (DBSCMA) and bis-adduct (DBSCBA) were synthesized using a classical cyclopropanation reaction via a tosylhydrazone route for application as acceptor materials in polymer solar cells (PSCs). DBSCBA shows good solubility in common organic solvents and both derivatives were characterized by 1HNMR, 13C NMR, MALD-TOF, elemental analysis and UV-vis absorption measurements. The shift of fullerene energy levels induced by the dibenzosuberane substitution was investigated by using theoretical simulations and ultraviolet photoelectron spectroscopy. Bulk-heterojunction PSCs based on poly (3-hexylthiophene) (P3HT) and dibenzosuberane-C60 derivatives were fabricated and optimized by adjusting the donor/acceptor ratio and using thermal annealing and solvent additive. The morphologies of the active layers processed under different conditions were also examined by atomic force microscopy. When tested under an illumination of AM 1.5 G at 100 mW/ cm2, the highest power conversion efficiency of the devices using DBSCBA is 3.70% which is superior to that of conventional P3HT:PCBM devices. © 2013 Elsevier B.V.
Open Access
Designing excited states: theory-guided access to efficient photosensitizers for photodynamic action
(2011) Cakmak, Y.; Kolemen, S.; Duman, S.; Dede, Y.; Dolen, Y.; Kilic, B.; Kostereli, Z.; Yildirim, L. T.; Dogan, A. L.; Guc, D.; Akkaya, E. U.
The in silico design of tetraradical S 1 states was validated experimentally through synthesis, followed by characterization including phosphorescence measurements, use of trap molecules, and cell culture studies, leading to a series of orthogonal dimers of Bodipy chromophores with remarkable singlet oxygen efficiencies (see picture). A new path for the rational development of efficient photosensitizers is thus revealed.
Open Access
Determination of trace element levels in human scalp hair in occupationally exposed subjects by XRF
(Akademiai Kiado Rt., 2001) Dede, Y.; Erten, H. N.; Zararsiz, A.; Efe, N.
Trace element levels in hair of individuals living in urban areas were determined by energy dispersive XRF. Two groups of subjects were investigated, the first group was assumed to be from a healthy environment, the other one was exposed to a high level of contamination due to working conditions. The results were compared to data reported in the literature. The concentrations of Ca, Fe, Cu, Zn and Pb in the scalp hair were determined and the correlation between hair trace element levels and environmental effects was discussed. The results given by the second group show that environmental exposure effects hair trace element levels which are related to body trace element concentrations.
Open Access
Heavy atom free singlet oxygen generation: doubly substituted configurations dominate S1 states of Bis-BODIPYs
(American Chemical Society, 2012) Duman, S.; Cakmak, Y.; Kolemen, S.; Akkaya, E. U.; Dede, Y.
S0, S1, and T1 states of various orthogonal 8,8′ and 8,2′-bis-boradiaza-s-indacene (BODIPY) dyes, recently (Angew. Chem., Int. Ed. 2011, 50, 11937) proposed as heavy atom free photosensitizers for O2(1 Δg) generation, were studied by multireference quantum chemical approaches. S0→S1 excitation characteristics of certain bis-BODIPYs are shown to be drastically different than the parent BODIPY chromophore. Whereas a simple HOMO→LUMO-type single substitution perfectly accounts for the BODIPY core, S1 states of certain orthogonal bisBODIPYs are described as linear combinations of doubly substituted (DS) configurations which overall yield four electrons in four singly occupied orbitals. Computed DS character of S1, strongly correlated with facile 1 O2 production, was presumed to occur via S1→T1 intersystem crossing (ISC) of the sensitizer. Further confirmation of this relation was provided by newly synthesized BODIPY derivatives and comparison of spectroscopic properties of their dimers and monomers. Near-IR absorption, desired for potential photodynamic therapy applications, was not pursuable for bis-chromophores by the standard strategy of π-extension, as DS singlet states are destabilized. Decreased exchange coupling in π-extended cases appears to be responsible for this destabilization. Comparisons with iodine incorporated bis-BODIPYs suggest that the dynamics of 1 O2 generation via DS S1 states are qualitatively different from that via ISC originating from heavy atom spin−orbit coupling. Although red-shifting the absorption wavelength to enter the therapeutic window does not seem attainable for orthogonal bisBODIPYs with DS S1 states, modifications in the chromophore cores are shown to be promising in fine-tuning the excitation characteristics.
Open Access
Intracellular modulation of excited-state dynamics in a chromophore dyad: differential enhancement of photocytotoxicity targeting cancer cells
(Wiley-VCH Verlag, 2015) Kolemen, S.; Işık, M.; Kim, G. M.; Kim D.; Geng, H.; Buyuktemiz, M.; Karatas, T.; Zhang, X. F.; Dede, Y.; Yoon, J.; Akkaya, E. U.
The photosensitized generation of reactive oxygen species, and particularly of singlet oxygen [O2(a1Dg)], is the essence of photodynamic action exploited in photodynamic therapy. The ability to switch singlet oxygen generation on/off would be highly valuable, especially when it is linked to a cancer-related cellular parameter. Building on recent findings related to intersystem crossing efficiency, we designed a dimeric BODIPY dye with reduced symmetry, which is ineffective as a photosensitizer unless it is activated by a reaction with intracellular glutathione (GSH). The reaction alters the properties of both the ground and excited states, consequently enabling the efficient generation of singlet oxygen. Remarkably, the designed photosensitizer can discriminate between different concentrations of GSH in normal and cancer cells and thus remains inefficient as a photosensitizer inside a normal cell while being transformed into a lethal singlet oxygen source in cancer cells. This is the first demonstration of such a difference in the intracellular activity of a photosensitizer.
Open Access
Ion responsive near-IR BODIPY dyes: two isomers, two different signals
(Royal Society of Chemistry, 2014) Ozdemir, T.; Kostereli, Z.; Guliyev, R.; Yalcin, S.; Dede, Y.; Akkaya, E. U.
Tetrastyryl-substituted BODIPY dyes are likely to evolve into a new class of near IR fluorophores. In this work we demonstrate that 1,7 and 3,5-positions show marked differences in charge transfer characteristics. Using a Hg(II) selective ligand, the signal transduction potentials were explored: one isomer shows a large blue shift in electronic absorption spectrum, while the other just shows an intensity increase in the emission spectrum. Electronic structure calculations were undertaken to elucidate the reasons for different signals on metal ion binding in relation to core BODIPY properties.
Open Access
A Noble-Metal-Free Heterogeneous Photosensitizer-Relay Catalyst Triad That Catalyzes Water Oxidation under Visible Light
(Wiley-VCH Verlag, 2018) Ulusoy-Ghobadi, Türkan Gamze; Yıldız, E. A.; Büyüktemiz, M.; Akbari, S. Sadigh; Topkaya, D.; İşçi, Ü.; Dede, Y.; Yağlioğlu, H. G.; Karadaş, Ferdi
An entirely earth-abundant chromophore-relay water oxidation catalyst triad system, which is robust and efficient at neutral pH, is presented. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with Co ions to prepare a covalently linked chromophore-Prussian blue analogue assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and it maintains a steady activity for at least three hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than a linker as it takes part in electron-transfer and co-operates with porphyrin in the charge separation process.
Open Access
A panchromatic boradiazaindacene (BODIPY) sensitizer for dye-sensitized solar cells
(2008) Erten Ela, S.; Yilmaz, M. D.; Icli, B.; Dede, Y.; Icli, S.; Akkaya, E. U.
(Chemical Equation Presented) A novel distyryl-substituted boradiazaindacene (BODIPY) dye displays interesting properties as a sensitizer in DSSC systems, opening the way to further exploration of structure-efficiency correlation within this class of dyes. © 2008 American Chemical Society.
Open Access
A robust, precious‐metal‐free dye‐sensitized photoanode for water oxidation: A nanosecond‐long excited‐state lifetime through a Prussian blue analogue
(Wiley-VCH Verlag, 2020-02) Ulusoy-Ghobadi, T. Gamze; Ghobadi, Amir; Büyüktemiz, M.; Akhüseyin Yıldız, E.; Yıldız, D. B.; Yağlıoğlu, H. G.; Dede, Y.; Özbay, Ekmel
Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal‐free, dye‐sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO2 and water oxidation catalysis. Our approach involves the use of a Fe(CN)5 bridging group not only as a cyanide precursor for the formation of a PB‐type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero‐functional PB‐modified TiO2 electrode demonstrates a low‐cost and easy‐to‐construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal‐free robust dye‐sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.
Open Access
Synthesis and dye sensitized solar cell applications of Bodipy derivatives with bis-dimethylfluorenyl amine donor groups
(Royal Society of Chemistry, 2015) Çakmak, Y.; Kolemen, S.; Buyuktemiz, M.; Dede, Y.; Erten-Ela, S.
Three Bodipy dyes with strong absorptivities in the visible and near infrared regions were designed, synthesized and their potential as photosensitizers for liquid electrolyte-based dye sensitized solar cells have been evaluated. For the first time Bodipy derivatives with bis-dimethylfluorenyl amine donor groups which were known for their bulky structures as donor groups have been used together. We altered our mostly used triphenylamine group with these and investigated the dye-sensitized solar cell efficiencies of this new class of Bodipy dyes. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015.
Open Access
Tuning the electronic properties of prussian blue analogues for efficient water oxidation electrocatalysis: experimental and computational studies
(Wiley-VCH Verlag, 2018) Alsaç, Elif Pınar; Ülker, E.; Nune, Satya Vijaya Kumar; Dede, Y.; Karadaş, Ferdi
Although several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process.
Open Access
Water oxidation electrocatalysis with a cobalt ‐ borate ‐ based hybrid system under neutral conditions
(Wiley-VCH Verlag, 2018) Turhan, Emine A.; Nune, Satya Vijaya Kumar; Ülker, E.; Şahin, U.; Dede, Y.; Karadaş, Ferdi
The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co3(BO3)2, with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co3(BO3)2@CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm−2 for Co3(BO3)2@CNT compared with 3.9 nmol cm−2 for Co3(BO3)2. Co3(BO3)2@CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm−2, respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions.