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Article Citation - WoS: 19Citation - Scopus: 18Deviations From Born-Oppenheimer Theory in Structural Chemistry: Jahn-Teller, Pseudo Jahn-Teller, and Hidden Pseudo Jahn-Teller Effects in C3h3< and C3h3<(Amer Chemical Soc, 2013) Kayi, H.; Garcia-Fernandez, P.; Bersuker, I. B.; Boggs, J. E.The electronic structure and vibronic coupling in two similar molecular systems, radical C3H3 and anion C3H3-, in ground and excited states, are investigated in detail to show how their equilibrium structures, in deviation from the Born-Oppenheimer approximation, originate from the vibronic mixing of at least two electronic states, producing the Jahn-Teller UT), pseudo JT (PJT), and hidden PJT effects. Starting with the high-symmetry geometry D3h of C3H3, we evaluated its 2-fold degenerate ground electronic state 2E" and two lowest excited states 2A,' and 2E' and found that all of them contribute to the distortion of the ground state via the JT vibronic coupling problem E" e' and two PJT problems (E" + A(1)') circle star e" and (E" + E') circle times (a2" + e"); all the three active normal modes e'(1335 e"(1030 cm(-1)), and a2"(778 cm(-1)) are imaginary, meaning that all the three vibronic couplings are sufficiently strong to cause instability, albeit in different directions. The first of them, the ground state JT effect, enhances one of the C-C bonds (toward an ethylenic form with C-2v symmetry), while the two PJT effects produce, respectively, cis (a(2)" toward C-3v symmetry) and trans (e") puckering of the hydrogen atoms. As a result, C3H3 has two coexisting equilibrium configurations with different geometry. In the C3H3- anion, the ground electronic state in DA symmetry is an orbitally nondegenerate spin triplet (3)A(2)' with a group of close in energy singlet and triplet excited states in the order of (1)A(1),', (3)A(1)', E-1", E-3", and E-1'. This shows that two PJT couplings, (3A(2)' + (3)A(1)") circle times a(2)" and (3A2' + 3E") e", may influence the geometry of the equilibrium structure in the 3A2' state. Indeed, both vibrational modes, a(2)"(1034 cm(-1)) and e"(1284 cm(-1)), are imaginary in this state. Similar to the radical case, they produce, respectively, cis (a(2)") and trans (e") puckering of the hydrogen atoms, but no e' distortion of the basic C-3 triangle; the equilibrium configuration with Cs symmetry occurs along the stronger e" distortions. Another higher-in-energy triplet-state minimum with C-2v symmetry emerges as a result of a strong JTE in the excited 3E" electronic state. In addition to these APES minima with spin-triplet electronic states, the system has a coexisting minimum with a spin-singlet electronic state, which is shown to be due to the hidden PJT effect that couples two singlet excited states. The two lowest equilibrium configurations of the C3H3- anion with different geometry and spin realize a (common to all electronic e(2) configurations) magnetic and structural bistability accompanied by a spin crossover. Some general spectroscopic consequences are also noted. As a whole, this article is intended to demonstrate the efficiency of the vibronic coupling approach in rationalizing the origin of complicated structural features of molecular systems as due to a combination of nonadiabatic JT effects.Article Citation - WoS: 28Citation - Scopus: 25Revealing the Effects of Defect States on the Nonlinear Absorption Properties of the Tlinsse and Tl2in2< Crystals in Near-Infrared Optical Limiting Applications(Amer Chemical Soc, 2024) Dogan, Anil; Karatay, Ahmet; Isik, Mehmet; Yildiz, Elif Akhuseyin; Gasanly, Nizami Mamed; Elmali, AyhanThe present study represents the effect of defect states on the nonlinear absorption and optical limiting performances of TlInSSe and Tl2In2S3Se single crystals with near-infrared excitations. The band gap energies were 2.2 and 2.22 eV, and the Urbach energies were 0.049 and 0.034 eV for TlInSSe and Tl2In2S3Se, respectively. The trapping time of localized defect states was found to be 8 ns by femtosecond transient absorption measurements. The analysis of open-aperture Z-scan data depends on two different fitting models to determine the effect of defect states on the nonlinear absorption (NA) properties of the studied crystals. Model 1 only considers two-photon absorption (TPA), while model 2 includes one-photon absorption (OPA), TPA, and free carrier absorption (FCA). The NA coefficients (ss(eff)) obtained from model 2 are higher than the values (ss) obtained from model 1 at the same intensities, revealing that defect states contribute to NA through OPA. The optical limiting properties of the TlInSSe and Tl2In2S3Se crystals were examined under 1064 nm wavelength excitation. The limiting thresholds were found to be 1.16 and 0.27 mJ/cm(2) at 29.8 GW/m(2) and 99.5 GW/m(2) input intensities, respectively. The results show that TlInSSe and Tl2In2S3Se crystals have promising potential for near-infrared optical limiting applications.Conference Object Acid/ Base Doped/ Dedoped Low Band Gap Polymer(Amer Chemical Soc, 2016) Karabay, Baris; Gokce, Gurcan; Cihaner, Atilla; Icli Ozkut, Merve[No Abstract Available]Article Citation - WoS: 48Citation - Scopus: 48A Pure Blue To Highly Transmissive Electrochromic Polymer Based on Poly(3,4-Propylenedioxyselenophene) With a High Optical Contrast Ratio(Amer Chemical Soc, 2015) Karabay, Baris; Pekel, Lutfiye Canan; Cihaner, AtillaA new derivative of 3,4-propylenedioxyselenophene bearing naphthalenylmethyl appeandages on the bridge, called 3,4-dihydro-3,3-bis((naphthalen-2-yl)methyl)-2H-selenopheno[3,4-b][1,4]dioxepine (ProDOS-Np-2), was synthesized and polymerized via potentiostatic and potentiodynamic methods. The electrochemically obtained polymer film (PProDOS-Np-2) is pure blue at the neutral state and highly transparent at the oxidized state. An increase in the size of the substituents on the bridge resulted in an increase in the optical contrast ratio. Upon moving from naked bridge to benzyl and to naphthalenylmethyl substituents on the bridge center, the optical contrast changed from 51% to 65% and finally to 84%, which is the second highest reported optical contrast ratio in polyselenophene family. When compared to polythiophene analogue, the PProDOS-Np-2 has lower oxidation potential and band gap, higher optical contrast ratio, coloration efficiency, robustness, and stability. The polymer film preserved its properties even after thousands of cycles under ambient conditions.Article Citation - WoS: 103Citation - Scopus: 108Copper(0) Nanoparticles Supported on Silica-Coated Cobalt Ferrite Magnetic Particles: Cost Effective Catalyst in the Hydrolysis of Ammonia-Borane With an Exceptional Reusability Performance(Amer Chemical Soc, 2012) Kaya, Murat; Zahmakiran, Mehmet; Ozkar, Saim; Volkan, MurvetHerein we report the development of a new and cost-effective nanocomposite catalyst for the hydrolysis of ammonia-borane (NH3BH3), which is considered to be one of the most promising solid hydrogen carriers because of its high gravimetric hydrogen storage capacity (19.6% wt) and low molecular weight. The new catalyst system consisting of copper nanoparticles supported on magnetic SiO2/CoFe2O4 particles was reproducibly prepared by wet-impregnation of Cu(II) ions on SiO2/CoFe2O4 followed by in situ reduction of the Cu(II) ions on the surface of magnetic support during the hydrolysis of NH3BH3 and characterized by ICP-MS, XRD, XPS, TEM, HR-TEM and N-2 adsorption-desorption technique. Copper nanoparticles supported on silica coated cobalt(II) ferrite SiO2/CoFe2O4 (CuNPs@SCF) act as highly active catalyst in the hydrolysis of ammonia-borane, providing an initial turnover frequency of TOF = 2400 h(-1) at room temperature, which is not only higher than all the non-noble metal catalysts but also higher than the majority of the noble metal based homogeneous and heterogeneous catalysts employed in the same reaction.. More importantly, they were easily recovered by using a permanent magnet in the reactor wall and reused for up, to 10 recycles without losing their inherent catalytic activity significantly, which demonstrates the exceptional reusability of the CuNPs@SCF catalyst.Article Citation - WoS: 47Citation - Scopus: 52Biocompatible Electroactive Tetra(aniline)-Conjugated Peptide Nanofibers for Neural Differentiation(Amer Chemical Soc, 2018) Arioz, Idil; Erol, Ozlem; Bakan, Gokhan; Dikecoglu, F. Begum; Topal, Ahmet E.; Urel, Mustafa; Guler, Mustafa O.Peripheral nerve injuries cause devastating problems for the quality of patients' lives, and regeneration following damage to the peripheral nervous system is limited depending on the degree of the damage. Use of nanobiomaterials can provide therapeutic approaches for the treatment of peripheral nerve injuries. Electroactive biomaterials, in particular, can provide a promising cure for the regeneration of nerve defects. Here, a supramolecular electroactive nanosystem with tetra(aniline) (TA)-containing peptide nanofibers was developed and utilized for nerve regeneration. Self-assembled TA conjugated peptide nanofibers demonstrated electroactive behavior. The electroactive self-assembled peptide nanofibers formed a well-defined three-dimensional nanofiber network mimicking the extracellular matrix of the neuronal cells. Neurite outgrowth was improved on the electroactive TA nanofiber gels. The neural differentiation of PC-12 cells was more advanced on electroactive peptide nanofiber gels, and these biomaterials are promising for further use in therapeutic neural regeneration applications.Article Citation - WoS: 52Citation - Scopus: 57Members of Cmy Color Space: Cyan and Magenta Colored Polymers Based on Oxadiazole Acceptor Unit(Amer Chemical Soc, 2012) Ozkut, Merve Icli; Algi, Melek Pamuk; Oztas, Zahide; Algi, Fatih; Onal, Ahmet M.; Cihaner, AtillaIn this study, three novel oxadiazole-based polymers were synthesized and their electrochemical and optical properties were investigated. The polymers were found to have both p- and n-type doping properties accompanied by electrochromic response. Two polymer films exhibit cyan and magenta colors, which constitute two legs of CMY color spaces, in their neutral states and they are soluble in common-organic solvents. According to the color mixing theory, all colors in the visible spectrum including black color can be obtained by using these polymers with a yellow colored electrochromic polymer. Among these polymers, the polymer bearing propyledioxythiophene donor units has some superior properties like high stability (it retains 94% of its electroactivity after 2000 cycles), solubility, and high coloration efficiency (230 cm(2)/C), whereas as expected ethylenedioxythiophene containing one has the lowest band gap as 1.08 eV.Article Citation - WoS: 4Citation - Scopus: 4Exploring the Thermal Stability of Sb2se3 for Potential Applications Through Advanced Thermal Analysis Methods(Amer Chemical Soc, 2025) Altuntas, Gozde; Isik, Mehmet; Surucu, Gokhan; Parlak, Mehmet; Surucu, OzgeAntimony selenide (Sb2Se3) is a promising material for energy applications, including photovoltaics, thermoelectrics, and photodetectors, due to its favorable electronic properties, availability, and low toxicity. However, its thermal stability, crucial for device efficiency and reliability, has been less explored, leaving a gap in understanding its high-temperature suitability. This study evaluates the thermal stability of Sb2Se3 using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The results show that Sb2Se3 remains stable up to 500 degrees C, with two significant weight loss stages: 1.75% between 500 and 610 degrees C, and 3.50% between 610 and 775 degrees C, indicating decomposition processes. Activation energies for the decomposition phases were determined as 121.8 and 57.2 kJ/mol using the Coats-Redfern method. Additionally, an endothermic phase transition was observed between 599 and 630.6 degrees C via DSC analysis. These findings demonstrate Sb2Se3's potential for high-temperature energy applications, providing essential insights for optimizing its use in solar cells, thermoelectric devices, and other technologies.Article Citation - WoS: 130Mnox< Pdag Alloy Nanoparticles for the Additive-Free Dehydrogenation of Formic Acid at Room Temperature(Amer Chemical Soc, 2015) Bulut, Ahmet; Yurderi, Mehmet; Karatas, Yasar; Say, Zafer; Kivrak, Hilal; Kaya, Murat; Zahmakiran, MehmetFormic acid (HCOOH) has a great potential as a safe and a convenient hydrogen carrier for fuel cell applications. However, efficient and CO-free hydrogen production through the decomposition of formic acid at low temperatures (<363 K) in the absence of additives constitutes a major challenge. Herein, we present a new heterogeneous catalyst system composed of bimetallic PdAg alloy and MnOx nanoparticles supported on amine-grafted silica facilitating the liberation of hydrogen at room temperature through the dehydrogenation of formic acid in the absence of any additives with remarkable activity (330 mol H-2 center dot mol catalyst(-1)center dot h(-1)) and selectivity (>99%) at complete conversion (>99%). Moreover this new catalytic system enables facile catalyst recovery and very high stability against agglomeration, leaching, and CO poisoning. Through a comprehensive set of structural and functional characterization experiments, mechanistic origins of the unusually high catalytic activity, selectivity, and stability of this unique catalytic system are elucidated. Current heterogeneous catalytic architecture presents itself as an excellent contender for clean hydrogen production via room-temperature additive-free dehydrogenation of formic acid for on-board hydrogen fuel cell applications.Article Citation - WoS: 81Citation - Scopus: 86New Approach for the Surface Enhanced Resonance Raman Scattering (serrs) Detection of Dopamine at Picomolar (pm) Levels in the Presence of Ascorbic Acid(Amer Chemical Soc, 2012) Kayat, Murat; Volkan, Murvet; Kaya, MuratThe development of a novel surface-enhanced resonance Raman scattering (SERRS) platform that allows fast and sensitive detection of dopamine (DA) has been reported. The iron-nitrilotriacetic acid attached silver nanoparticle (Ag-Fe(NTA)) substrate provides remarkable sensitivity and reliable repeatability. The advantages of both the surface functionalization for specific analytes and the SERRS are integrated into a single functional unit. While the silver core gives the necessary enhancing properties, the Fe-NTA receptors can trap DA adjacent the silver core and the NTA-Fe-DA complex formed provides resonance enhancement with a 632.8 nm laser. DA could be detected in pM level without any pretreatment with a reliable discrimination against AA, by utilizing low laser power (10 mW) and short data acquisition time (10 s). The high sensitivity along with the improved selectivity of this sensing approach is a significant step toward molecular diagnosis of Parkinson's disease.
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