Browsing by Author "Ekmekci, Zeynep"

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Excited State Intramolecular Proton Transfer (esipt)-Based Sensor for Ion Detection
(Springer/plenum Publishers, 2021) Kuzu, Burak; Ekmekci, Zeynep; Tan, Meltem; Menges, Nurettin
C-2 and C-5 substituted imidazole skeleton was synthesized through a one-pot two-step strategy. Synthesized molecule emits the light on ESIPT (excited-state intramolecular proton transfer). This molecule was utilized for its proton donor ability, and we have observed that fluoride and cyanide ions can be detected selectively. Different cations and anions were selected to observe the response of the synthesized molecule. However, there were not any fluorometric and colorimetric response except for fluoride and cyanide ions. Detection limits of fluoride and cyanide ions were found to be 9.22 mu M and 11.48 mu M, respectively. H-1-NMR spectra for the solution of the sensor and TBAF (tetrabuthylammoniumfluoride) were used for the identification of [L](-)[HF2](-) species. 3 equiv. TBAF saturated the solution of the sensor in d(6)-DMSO, and some of the proton resonances shifted to upfield due to the through-bond effect. The disappearance of NH proton with 0.5 equiv. TBAF or TBACN (tetrabuthylammoniumcyanide) showed that there was a proton abstraction by fluoride and cyanide ions, instead of the hydrogen bond. Solid-state application was utilized, and paper test strips were applied. Emission differences emerged when the sensor loaded strips were reacted with TBAF. Time resolved experiments revealed that solution of the sensor and TBAF in DMSO have multiexponential decay, and one of the lifetime was measured as 13.4 ns.
Exploring of Indole Derivatives for Esipt Emission: a New Esipt-Based Fluorescence Skeleton and Td-Dft Calculations
(Elsevier Science Sa, 2021) Kaya, Serdal; Aydin, Hatice Gulten; Keskin, Selbi; Ekmekci, Zeynep; Menges, Nurettin
ABS T R A C T Appropriate synthesis methods gave six different indole derivatives substituted at the C-2 or C-3 position. ESIPT emission capacities of these derivatives were investigated. It was concluded that the indole derivative containing the 1,2-dicarbonyl group at the C-2 position has ESIPT emission. Although adding water to the DMSO solution of the ESIPT-based molecule (9:1) resulted in ESIPT quenching, steady-state measurements in MeOH did not occur ESIPT quenching. TD-DFT calculation for uncovering the ESIPT mechanism emerged that the ESIPT mechanism occurred as a barrierless process. The X-ray analysis and DFT conformational analysis revealed that NH and CO groups involving proton transfer mechanisms are in the cis position. A mono-exponential decay was observed in DMSO and MeOH solutions, in which lifetimes were measured as 6.1 and 5.5 ns, respectively. pH studies revealed that acidic and basic solutions of molecule 7 did not influence ESIPT emission.
A Novel Fluorescent Sensor Based on Imidazole Derivative for Fe3+ Ions
(Elsevier, 2017) Kuzu, Burak; Tan, Meltem; Ekmekci, Zeynep; Menges, Nurettin
In this work, a new imidazole-based sensitive and selective sensor was synthesized. It was observed that the synthesized new fluorescent sensor had high selectivity and sensitivity to Fe3+ ions. The association constant of the sensor was found by using Stern Volmer Plot as 14,318 M-1. Binding stoichiometry between sensor and Fe3+ ions was found by using Job's plot as 1:1. The synthesized chemical sensor was found to exhibit a large Stokes' shift (107 nm). The proposed turn-OFF mechanism regarding bonding between sensor and Fe+3 ions was discussed by NMR data and DFT calculations. Furthermore, it was revealed that planarity and functional groups such as methoxy and carbonyl affected the quantum yield. These results were confirmed by plotting of Frontier orbitals and calculated dihedral angles.
A Novel Structure for Esipt Emission: Experimental and Theoretical Investigations
(Elsevier Science Sa, 2019) Kuzu, Burak; Tan, Meltem; Ekmekci, Zeynep; Menges, Nurettin
A number of substituted imidazole-based molecules were synthesized via a two-step one-pot reaction and their UV/vis and fluorescence spectra were analyzed. Emissions of the imidazole-based molecules were attributed to the excited state intramolecular proton transfer (ESIPT) process. Imidazole-based sensor molecules have high Stokes shifts which is good clue for the ESIPT mechanism. Furthermore, the ESIPT mechanism was confirmed by some control experiments in which acceptor and donor groups were functionalized, resulting in hampered ESIPT emission. Time-resolved experiments showed that the skeleton synthesized had different exponential decays depending on the functional groups (OMe and OH). According to the time-resolved experiments, the ESIPT reaction occurred between 1.0 and 3.10 ns. Furthermore, the lifetime of molecules in EtOH increased when the phenyl ring possessed OMe or OH groups. Dihedral angles between the NH and carbonyl groups were calculated and found to be important for a stable configuration. The methyl substituted NH group on the imidazole skeleton in which the ESIPT reaction should be interrupted, revealed a 0.3 ns lifetime in DMSO. Potential energy curves for all compounds were analyzed using TD-DFT. It was seen that there is no barrier for excited state proton transfer resulting in ultrafast ESIPT process.