Browsing by Author "Ozcelik, Serdar"

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Composites of Reactive Silica Nanoparticles and Poly(glycidyl methacrylate) with Linear and Crosslinked Chains by in situ Bulk Polymerization
(Vsp Bv, 2010) Demir, Mustafa M.; Altin, Burcu; Ozcelik, Serdar
Composites of poly(glycidyl methacrylate) (PGMA) and L-lysine-coated silica nanoparticles with varying contents were prepared by in situ bulk polymerization using benzoyl peroxide (BPO) as free radical initiator. Silica nanoparticles covered by L-lysine molecules were synthesized using emulsion method. Dynamic light scattering measurements confirmed that the particles are highly monodisperse with the diameter of 10 nm and free of aggregates in the monomer (glycidyl methacrylate, GMA). Upon polymerization of the homogeneous particle/monomer dispersion, aggregates of individual silica nanoparticles are observed by tapping mode atomic force microscope (AFM). Amine and/or carboxylic acid sites on particle surface covalently react with the oxirane groups of the polymer backbone. The aggregation was substantially suppressed by using a difunctional comonomer divinyl benzene (DVB) in polymerization. A three-dimensional polymer network, P(GMA-DVB), forms throughout the system. This structure leads to significant progress in particle dispersion, therefore in physical properties of the resulting composite. We demonstrated that the composites prepared by crosslinked chains are thermally more stable and mechanically stiffer than those prepared by linear ones. (C) Koninklijke Brill NV, Leiden, 2010
Controlling Spontaneous Emission of CdSe Nanoparticles Dispersed in Electrospun Fibers of Polycarbonate Urethane
(Amer Chemical Soc, 2009) Demir, Mustafa M.; Soyal, Duygu; Unlu, Caner; Kus, Mahmut; Ozcelik, Serdar
Luminescent fibrous composite films consisting of submicrometer diameter fibers were prepared by electrospinning of segmented polycarbonate urethane (PCU) in dimethyl formamide and tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals (5 nm in diameter) in toluene. Using a pair of conductive electrodes separated with an air gap, we successfully produced randomly deposited and uniaxially aligned electrospun fibers. The surface structure of the electrospun fibers was studied using atomic force microscopy (AFM) and was compared to the corresponding film prepared by casting. In cast film, tapping mode AFM imaging suggests that hard urethane segments organize into rodlike morphology dispersed in soft polycarbonate. When PCU/CdSe dispersions were subjected to electrospinning, copolymer domains were forced to arrange into lamella along the fiber axis due to elongational flow and high stretching. Molecular orientation in the domains of the composite fibers was confirmed by polarized infrared spectroscopy. We demonstrated that formation of the oriented domains by electrospinning develops a hierarchical structure, which consequently modifies spectral properties because new multiple sharp lines appeared in the photoluminescence (PL) spectra of the fibers. In contrast to randomly deposited fibers, the PL intensity of uniaxially aligned fibers was found to be angle dependent. We propose that the elongated internal structure within the fibers controls the spontaneous emission of CdSe nanoparticles dispersed throughout the electrospun mat. A discussion on the nature of the controlled spontaneous emission is provided.
Development of AB3-Type Novel Phthalocyanine and Porphyrin Photosensitizers Conjugated with Triphenylphosphonium for Higher Photodynamic Efficacy
(Amer Chemical Soc, 2022) Onal, Emel; Tuncel, Ozge; Vatansever, Ipek Erdogan; Albakour, Mohamad; Celik, Gizem Gumusgoz; Kucuk, Tugba; Ozcelik, Serdar
There are a number of lipophilic cations that can be chosen; the triphenylphosphonium (TPP) ion is particularly unique for mitochondrion targeting, mainly due to its simplicity in structure and ease to be linked to the target molecules. In this work, mitochondrion-targeted AB3-type novel phthalocyanine and porphyrin photosensitizers (PSs) were synthesized and their photophysical photochemical properties were defined. Fluores-cence quantum yields (phi F) are 0.009, 0.14, 0.13, and 0.13, and the singlet-oxygen quantum yields (phi Delta) are 0.27, 0.75, 0.57, and 0.58 for LuPcPox(OAc), AB3TPP-Pc, AB3TPP-Por-C4, and AB3TPP-Por-C6, respectively. To evaluate the photodynamic efficacy of the TPP-conjugated PS cell viabilities of A549 and BEAS-2B lung cells were comparatively measured and IC-50 values were determined. AB3TPP-Por-C4, AB3TPP-Por-C6, and AB3TPP-Pc compounds compared to the reference molecules ZnPc and H2TPP were found to be highly cytotoxic (sub-micromolar concentration) under the light. LuPcPox(OAc) is the most effective molecule regarding cell killing (the activity). The cell killing of the TPP-conjugated porphyrin derivatives exhibits a similar response compared to LuPcPox(OAc) when the light absorbing factor of the PS is normalized at 660 nm: TPP-conjugated porphyrins absorb less light (lower extinction coefficient) but produce more radical species (higher singlet-oxygen quantum yield) and therefore effectively kill the cells. The singlet oxygen-producing capacity of AB3TPP-Pc is almost 3 times higher compared to LuPcPox(OAc) and 50% more efficient with respect to ZnPc, suggesting that TPP-conjugated phthalocyanine may serve as a good photosensitizer for photodynamic therapy (PDT). The high singlet oxygen generation capacity of these novel TPP-conjugated porphyrin and phthalocyanine PS suggests that they might be useful for PDT requiring lower photosensitizer concentration and reduced energy deposited through less light exposure.
Enhanced light-matter interaction in a hybrid photonic-plasmonic cavity
(Springer Heidelberg, 2021) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci
Strongly concentrated optical fields around a metal nanoparticle in the close vicinity of a dipole noticeably facilitate dramatic changes in the localized density of states due to hybrid photonic-plasmonic mode couplings as compared to that of the pure cavity mode fields. Significant variations of the field intensity in the presence of the metal nanoparticle elucidate enhanced light-matter interaction in a hybrid structure. The enhancement factor of the light-matter interaction is studied through the single-atom cooperativity parameter, which is directly proportional to the ratio of the fluorescence lifetimes of the off-resonant and on-resonant emission. A compact and cost-effective hybrid device, which includes a microfiber cavity, supporting whispering gallery modes, and a well-defined solid nanostructure, consisting of a gold nanoparticle core, overcoated by a silica shell, and decorated with CdS/CdSe quantum dots, is demonstrated to offer an outstanding potential for the enhancement of light-matter interaction. Surface plasmons of a gold nanoparticle, placed inside a hollow cylindrical nanostructure at the surface of a microfiber, are activated upon excitation of the dipoles of the quantum emitters, which are on-resonance with the whispering gallery mode. Time-resolved experiments demonstrate that the single-atom cooperativity parameter of the quantum dots is enhanced by a factor of about 4.8 in the presence of the gold nanoparticle being simultaneously in strong interaction with the cavity mode field and the metal nanoparticle's surface plasmons.
Enhanced light-matter interaction in a hybrid photonic-plasmonic cavity (vol 127, 907, 2021)
(Springer Heidelberg, 2022) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci
[No Abstract Available]
Enhanced Spontaneous Emission Rate in a Low-Q Hybrid Photonic-Plasmonic Nanoresonator
(Amer Chemical Soc, 2019) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Unluturk, Secil S.; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci
In this paper, CdTe quantum dots (QDs)-doped single electrospun polymer nanofibers are partially coated with gold nanoparticles to form distinct hybrid photonic-plasmonic nanoresonators to investigate the critical role of the cavity-confined hybrid mode on the modification of the spontaneous emission dynamics of the fluorescent emitters in low-Q photonic cavities. A total enhancement factor of 11.2 is measured via a time-resolved experimental technique, which shows that there is an increase of about three times in the spontaneous emission rate for the QDs-doped gold nanoparticle-decorated nanofibers as they are compared with those uncoated ones. The physical mechanism affecting the spontaneous emission rate of the encapsulated QDs in such a hybrid photonic-plasmonic nanoresonator is explained to be due to regeneration of the mode field in the nanofiber cavity upon the interaction of the dipoles with the surface plasmons of distinctive gold nanoparticles that surround the outer surface of the nanofiber.
Enthalpy-driven selective loading of CdSe_0.75S_0.25 nanoalloys in triblock copolymer polystyrene-b-polyisoprene-b-polystyrene
(Elsevier Science Bv, 2016) Askin, Gorkem; Cecen, Volkan; Unluturk, Secil Sevim; Ozcelik, Serdar; Demir, Mustafa M.
CdSe0.25S0.25 nanoalloys were blended with asymmetric triblock copolymer of polystyrene-bpolyisoprene-b-polystyrene(PS-SIS) in tetrahydrofuran. The fraction of styrene block varies from 14 to 22% with respect to isoprene by mass. The morphology of the copolymer cast film experiences a phase change from cylinder to lamella. CdSe0.25S0.25 nanoalloys were prepared by two-phase method. The surface of the nanoalloys was capped by either oleic acid (OA) or n-tri-octylphosphonic acid (TOPO) in situ. The mean diameter of the alloyed particles is around 12 nm in both systems. The chemical nature of the nanoalloy surface was found to influence the dispersion of the particles over polymer volume. The size of the nanoalloy domains in PS is 50 nm, on average, consisting of approximately 0.7 wt% nanoalloys. However, the size of the nanoalloy domains is smaller when they are loaded into PS-SIS. The structure formation is predominantly determined by enthalpic compatibilization. Atomic force microscopy results suggest that the nanoalloys capped with TOPO sequester into PS-rich domains and enlarge the domain. On the other hand, the ones capped with OA prefer to locate in polyisoprene domains. The increase of particles over 1.0 wt% distorts the lamella structure. (C) 2016 Elsevier Ltd. All rights reserved.
Formation of Pseudoisocyanine J-Aggregates in Poly(vinyl alcohol) Fibers by Electrospinning
(Amer Chemical Soc, 2009) Demir, Mustafa M.; Ozen, Bengisu; Ozcelik, Serdar
Submicrometer diameter, light emitting fibers of poly(vinyl alcohol) (PVA) doped with pseudoisocyanine (1, 1'-diethyl-2,2'-cyanine bromide, PIC) dye were prepared by electrospinning. A horizontal setup was employed with a stationary collector consisting of two parallel-positioned metal strips separated by a void gal). Formation of uniaxially aligned and randomly deposited fibers in electrospun films was confirmed by microscopy. Photoluminescence (PL) spectroscopy is used to evaluate spectral properties of both types of fibers doped with PIC. While PIC molecules were individually dispersed in PVA Solution, they assemble into J-aggregates upon electrospinning when the weight fraction of PIC molecules is above 2.5 wt%. The formation of J-aggregates was observed in both randomly deposited and Uniaxially aligned electrospun fibers. Moreover, the fibers aligned uniaxially showed a high degree of polarized emission (PL(parallel to)/PL(perpendicular to) = 10), arising from the orientation of J-aggregates along the fiber axis. On the other hand, isotropic emission of J-aggregates was observed from the fibers deposited randomly. As a conclusion, electrospinning was found to be an efficient and a practical method to form highly oriented J-aggregates dispersed into polymer fibers. To the best Of Our knowledge, it is the first time formation of J-aggregates (a bottom-up approach) and electrospinning (a top-down approach) is successfully combined.
Hybrid photonic-plasmonic mode-coupling induced enhancement of the spontaneous emission rate of CdS/CdSe quantum emitters
(Elsevier, 2022) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci
In this paper, a hybrid photonic-plasmonic resonator, which comprises an electrospun polymer fiber with a micrometer diameter and a core/shell nanostructure with a gold nanoparticle core, is constructed to investigate the dynamics of the coupled spontaneous emission of CdS/CdSe quantum dots (QDs). The gold nanoparticle core; covered with a silica shell, anchored with individual CdS/CdSe QDs, is placed inside a hollow cylindrical nanocavity formed on the surface of the microfiber to enable integration of the optical mode with the plasmonic effect, which is induced by the localized surface plasmons of the metal nanoparticle being present in the vicinity of the dipoles. The spontaneous emission rate of the QDs, coupled into the hybrid photonic-plasmonic mode, is measured to enhance by a factor of 23 via a time-resolved experimental technique. This result suggests that the regeneration of the optical mode-field inside the photonic-plasmonic resonator through the interaction of the dipoles with the localized surface plasmons of a metal nanoparticle strongly enhances the density of the elec-tromagnetic states of the quantum emitters to facilitate an enhanced spontaneous emission within the host medium of the proposed polymer based-photonic structure.