Nurgül Seferoğlu

Re-entrant phase transitions of the Blume–Emery–Griffiths model for a simple cubic lattice on the cellular automaton

The spin-1 Ising (BEG) model with the nearest-neighbor bilinear and biquadratic interactions and single-ion anisotropy is simulated on a cellular automaton which is improved from the Creutz cellular automaton (CCA) for a simple cubic lattice. The simulations have been made for several sets of parameters K/J and D/J in the -3<D/J⩽0 and -1⩽K/J⩽0 parameter regions. The re-entrant and double re-entrant phase transitions of the BEG model are determined from the temperature variations of the thermodynamic quantities (M, Q and χ). The phase diagrams characterizing phase transitions are compared with those obtained from other methods.

Critical exponents of the three-dimensional Blume–Capel model on a cellular automaton

The static critical exponents of the three-dimensional Blume–Capel model which has a tricritical point at D/J=2.82 value are estimated for the standard and the cooling algorithms which improved from Creutz cellular automaton. The analyses of the data using the finite-size scaling and power-law relations reproduce their well-established values in the D/J<3 and D/J<2.8 parameter region at standard and cooling algorithms, respectively. For the cooling algorithm at D/J=2.8 value of single-ion anisotropy parameter, the static critical exponents are estimated as β=0.31, γ=γ′=1.6, α=α′=0.32 and ν=0.87. These values are different from β=0.31, γ=γ′=1.25, α=α′=0.12 and ν=0.64 universal values. This case indicated that the BC model exhibits an ununiversal critical behavior at the D/J=2.8 parameter value near the tricritical point (D/J=2.82). The simulations were carried out on a simple cubic lattice with periodic boundary conditions.

Phenylazoindole dyes – Part I: The syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties

In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, (1)H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using (1)H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.

Finite Size Effect for the First-Order Phase Transition of the Three-Dimensional Blume--Capel Model on a Cellular Automaton

The first-order phase transition of the three-dimensional Blume–Capel model is investigated using the cooling algorithm which is improved from Creutz Cellular Automaton at D/J = 2.9, i.e. a ratio of single-ion anisotropy constant to bilinear interaction energy. We test the efficiency of the algorithm and obtain the finite-size effects at the first-order phase transition point. The transition temperature is estimated using the probability distributions of the order parameter and the energy. The analysis of data at the transition point indicates that the magnetic susceptibility and the specific heat maxima increase with the system value (Ld).

Switching off the charge transfer and closing the S1-T1 ISC channel in excited states of quinolizinium derivatives: a theoretical study.

Excited states of benzo[b]quinolizinium (BQ) derivatives that show efficient pH-responsive fluorescence switching properties were studied quantum-chemically by employing the CASSCF/CASPT2 and TD-DFT methods. Protonation of aminophenyl-BQ at the electron-donor amine moiety converts the nitrogen lone pair into a σ bond and the HOMO into a lower-lying orbital that is no longer involved in the excitation, thereby rationalizing the suppression of the charge transfer. An S1-T1 seam between the vertically excited Franck-Condon (FC) point and the S1 equilibrium geometry favors intersystem crossing (ISC). The T1 state of the protonated form remains well below S1 (1.5 eV) because of favorable exchange interactions, whereas the T1 state of the unprotonated form does not experience any analogous stabilization because of the difference in the spatial domains of the singly occupied orbitals in the S1 and T1 states. The S1 surface from the FC point until the equilibrium geometry for the protonated species is energetically downhill. Calculations on models and available experimental data suggest design principles for similarly functioning pH-responsive species, namely, an amine lone pair as the electron donor and a cationic ring of moderate size as the electron acceptor that are structurally separated by virtue of a spacer.

New platinum (II) and palladium (II) complexes of coumarin-thiazole Schiff base with a fluorescent chemosensor properties: Synthesis, spectroscopic characterization, X-ray structure determination, in vitro anticancer activity on various human carcinoma cell lines and computational studies

A new coumarin-thiazole based Schiff base (Ligand, L) and its Pd(II), Pt(II) complexes; ([Pd(L)2] and [Pt(L)2]), were synthesized and characterized using spectrophotometric techniques (NMR, IR, UV-vis, LC-MS), magnetic moment, and conductivity measurements. A single crystal X-ray analysis for only L was done. The crystals of L have monoclinic crystal system and P21/c space group. To gain insight into the structure of L and its complexes, we used density functional theory (DFT) method to optimize the molecules. The photophysical properties changes were observed after deprotonation of L with CN- via intermolecular charge transfer (ICT). Additionally, as the sensor is a colorimetric and fluorimetric cyanide probe containing active sites such as coumarin-thiazole and imine (CH=N), it showed fast color change from yellow to deep red in the visible region, and yellow fluorescence after CN- addition to the imine bond, in DMSO. The reaction mechanisms of L with CN-, F- and AcO- ions were evaluated using 1H NMR shifts. The results showed that, the reaction of L with CN- ion was due to the deprotonation and addition mechanisms at the same time. The anti-cancer activity of L and its Pd(II) and Pt(II) complexes were evaluated in vitro using MTT assay on the human cancer lines MCF-7 (human breast adenocarcinoma), LS174T (human colon carcinoma), and LNCAP (human prostate adenocarcinoma). The anti-cancer effects of L and its complexes, on human cells, were determined by comparing the half maximal inhibitory concentration (IC50) values. The activity results showed that, the Pd(II) complex of L has higher anti-tumor effect than L and its Pt(II) complex against the tested human breast adenocarcinoma (MCF-7), human prostate adenocarcinoma (LNCAP), and human colon carcinoma (LS174T) cell lines.

Simulation of Spin-3/2 Blume—Capel Model on a Cellular Automaton with Heating and Cooling Algorithm

The spin-3/2 Blume—Capel model is studied using the heating and cooling algorithms improved from the Creutz cellular automaton (CCA). The calculations are done on various sizes of the simple cubic lattice in the 0 ≤ D/J ≤ 5 parameter region. The phase diagram of the model and temperature variation of the thermodynamic quantities are obtained. We confirm the existence of a critical end point within the heating calculations. However, in contrast to the heating calculations, we do not obtain the first-order line at low temperature with cooling algorithm calculations. The results are compared with those of other theories.

The ferrimagnetic phase of the Blume-Emery-Griffiths model on the cellular automaton

The Blume-Emery-Griffiths model is simulated using the cooling algorithm which is improved from the Creutz cellular automaton (CCA) under periodic boundary conditions. The simulations are carried out on a simple cubic lattice at K/J = −1.5 in the range of −3.5 < D/J < 0.5, with J and K representing the nearestneighbour bilinear and biquadratic interactions, D being the single-ion anisotropy parameter. The phase diagram characterizing phase transition of the model is obtained. We found different kinds of phase transitions between the ferromagnetic, quadrupolar, staggered quadrupolar and ferrimagnetic phases for K/J = −1.5. In particular, the region of the phase diagram containing a ferrimagnetic phase is explored and compared to those obtained by other methods. The simulations confirm that the ferrimagnetic phase occurs in the narrow interval −3.006 ≤ D/J < −3. This result is in a good agreement with Monte Carlo renormalization group and closer to the cluster variation method result than the mean field approximation result.

Critical Exponents for the Re-entrant Phase Transitions in the Three-Dimensional Blume?Emery?Griffiths Model on the Cellular Automaton

The critical behaviour of the three-dimensional Blume–Emery–Griffiths (BEG) model is investigated at D/J = 0, -0.25 and -1 in the range of −1≤K/J≤0 for J = 100. The simulations are carried out on a simple cubic lattice using the heating algorithm improved from the Creutz cellular automaton (CCA) under periodic boundary conditions. The universality of the model are obtained for re-entrant and double re-entrant phase transitions which occur at certain D/J and K/J parameters, with J and K representing the nearest-neighbour bilinear and biquadratic interactions, and D being the single-ion anisotropy parameter. The values of static critical exponents β, γ and ν are estimated within the framework of the finite-size scaling theory. The results are compatible with the universal Ising critical behaviour for all continuous phase transitions in these ranges.

Triphenylamine-based allylidenemalononitrile chromophores: synthesis, and photophysical and second-order nonlinear optical properties

A series of chromophores based on a mono-, di- or tri-substituted triphenylamine core and allylidenemalononitrile fragments has been designed. The linear and second order nonlinear optical properties as well as thermal stability of the chromophores have been studied experimentally. Structure–property relationships, in terms of the branching effect on the triphenylamine core and the influence of the aniline/coumarin part on the photophysical properties and NLO response, have been highlighted. The experimental results have been rationalized by theoretical calculations.