You are invited to CHEM 591 – Graduate Student Seminars of Chemistry Department.
This week’s speakers are Gizem Yıldız, Ertan İşsever and Fatma Altuğ.
Please see the seminar information and the abstracts below.
1.Systematic Investigation of Intramolecular Through-Space Charge Transfer in Naphthalene-Based Systems with Various Donor and Acceptor Moieties
Gizem Yıldız
Advisor: Asst. Prof. Yunus Emre Türkmen
Time: May 06, 2025, 12:30, SBZ14
Abstract: Charge transfer is the transition between two states with different charge densities, which involves electron donor-acceptor moieties, and the redistribution of charges is the core concept of such excited states.1 Our group has recently designed a novel scaffold that facilitates intramolecular through-space charge transfer, incorporating a naphthalene spacer, benzofuran as electron donor moiety, and various ynone groups as electron acceptor moiety that have a CT band in the visible region in their UV-Vis and fluorescence spectra.2 In this work, our aim is to investigate how electronic structures, spatial positioning, and electron density differences influence charge transfer behavior by synthesizing a range of substrates with varying electron-donating and electron-accepting groups. With this purpose, we utilize Sonogashira and Suzuki coupling reactions to synthesize the target compounds and examine the charge transfer properties with the help of UV-Vis and fluorescence spectra.
2.Non-Additive Ion Effects of Greasy Cations and Weakly Hydrated Anions on Aqueous Macromolecules
Ertan İşsever
Advisor: Asst. Prof. Halil İ. Okur
Time: May 06, 2025, 12:30, SBZ14
In the late 19th century, Franz Hofmeister first studied the interactions of ions with macromolecules. The effects of different ions on macromolecules, especially on proteins, are presented in an ion-specific series. However, the interaction mechanisms of ions with macromolecules have not been fully understood at the molecular level.¹ Generally, it is shown that anions have the dominant influence, while cations are mostly considered to serve to balance the charge. Recently, the Okur group reported that more bulky tetraalkyl ammonium cations could interact with macromolecules as strongly as weakly hydrated anions (SCN-).² Herein, salts of weakly hydrated ions – tetraalkyl ammonium (NR₄⁺) and iodide (I⁻) – were studied to elucidate the fundamentals of tunable ion-macromolecule interactions via employing poly(N-isopropyl acrylamide) (PNIPAM) macromolecules. These ions are also known to be surface active and show salting-in behavior on macromolecules. By utilizing a multinstrumental approach, we explored this system. The phase transition temperature measurements showed an enhanced salting-in behavior for tetraethyl ammonium (NEt₄⁺) and tetrapropyl ammonium (NPr₄⁺) iodide salts. Surprisingly, tetrabutyl ammonium (NBu₄⁺) iodide showed an explicit salting-out behavior. NMR and ATR-FTIR experiments demonstrated that in the presence of NBu₄I, both the cation and the anion interact with the macromolecules. The simultaneous and cooperative interaction of the anion and cation gives rise to many oppositely charged surface sites and causes a (stabilizing) collapsed state. These findings represent the first example of a weakly hydrated cation-dominant ion interaction mechanism in aqueous macromolecules
3.Separation of Ion and Electron Transfer in Conducting Polymer Films
Fatma Altuğ
Advisor: Assoc. Prof. Burak Ülgüt
Time: May 06, 2025, 12:30, SBZ14
Abstract: This study aims to elucidate the electron transfer mechanism in conducting polymers and to explain the slow switching behavior observed in electrochromic materials, despite rapid electron hopping between redox centers. Although electron and ion transfer are coupled, ion movement is considerably slower and often limits the overall switching speed. In electroactive films, redox reactions trigger the oxidation and reduction of the polymer, accompanied by the movement of counter-ions from the electrolyte into the film. This ion motion, governed by the principle of charge neutrality, has been confirmed in previous studies using operando Na NMR techniques. (Lyu et al., 2023)
Here, we combine operando UV-VIS spectroscopy with cyclic voltammetry to isolate and monitor charge accumulation resulting solely from faradaic reactions by varying the voltage sweep rate. At high scan rates, ion oscillation increases, and beyond a certain frequency, ion movement is expected to halt, disrupting charge neutrality. This study aims to demonstrate that, under these conditions, electron transfer can still occur by overcoming coulombic repulsion, challenging the conventional understanding of ion-electron coupling Experimentally, spectro-electrochemical measurements were carried out across a wide range of sweep rates, from slow to ultrafast using polymer films of varying thickness. This allowed us to investigate the effect of film thickness on the observed electrochemical and optical responses.
Data analysis begins with Principal Component Analysis (PCA), which identifies the number of independent optical states needed to model the UV-VIS spectra. Although multi-parameter fitting can be performed using basis set components, our goal is to determine only physically meaningful parameters. The results show that for thin films, two components are sufficient to fit the absorbance spectra across the 200–1200 nm range, while three components are needed for thicker films. Notably, while isosbestic points are clearly observed in thin films, thick films display a transient isosbestic point around 750 nm at slow scan rates (e.g., 2 mV/s), which disappears as the redox process continues.
Assuming that absorbance changes arise solely from faradaic reactions, the mathematical coefficients obtained from spectral fitting can be correlated with redox current. This correlation also holds as scan rate increases: while the relative degree of color change decreases, it does not vanish completely, suggesting a limiting value. This indicates that even in the absence of ideal ion compensation, some degree of electron transfer persists, implying that Coulombic forces can be overcome. Understanding the mechanism enabling such transfer—despite the lack of complete ion balancing—is a key focus of this study.
In the modeling section, we develop a framework based on the Nernst–Planck–Poisson equations and redox kinetics, implemented via Newman’s BAND matrix method. Simulations of cyclic voltammetry under this model aim to disentangle capacitive and faradaic currents, providing insight into the redox dynamics of the polymer system. Unlike prior approaches, we aim to calibrate model parameters using experimental data and to establish a reliable baseline for capacitive current. This allows a more accurate quantification of faradaic processes, especially through the analysis of peak current as a function of sweep rate.
This methodology is broadly applicable—not only to conducting polymers but also to a wide range of electroactive materials—offering an improved approach to interpreting charge transport mechanisms and enabling more accurate b-value analysis in electrochemical systems.