Onur Buyukcakir

Elemental-Sulfur-Mediated Facile Synthesis of a Covalent Triazine Framework for High-Performance Lithium–Sulfur Batteries

A covalent triazine framework (CTF) with embedded polymeric sulfur and a high sulfur content of 62 wt % was synthesized under catalyst- and solvent-free reaction conditions from 1,4-dicyanobenzene and elemental sulfur. Our synthetic approach introduces a new way of preparing CTFs under environmentally benign conditions by the direct utilization of elemental sulfur. The homogeneous sulfur distribution is due to the in situ formation of the framework structure, and chemical sulfur impregnation within the micropores of CTF effectively suppresses the dissolution of polysulfides into the electrolyte. Furthermore, the triazine framework facilitates electron and ion transport, which leads to a high-performance lithium-sulfur battery.

Charged Covalent Triazine Frameworks for CO2 Capture and Conversion

The quest for the development of new porous materials addressing both CO2 capture from various sources and its conversion into useful products is a very active research area and also critical in order to develop a more sustainable and environmentally-friendly society. Here, we present the first charged covalent triazine framework (cCTF) prepared by simply heating nitrile functionalized dicationic viologen derivatives under ionothermal reaction conditions using ZnCl2 as both solvent and trimerization catalyst. It has been demonstrated that the surface area, pore volume/size of cCTFs can be simply controlled by varying the synthesis temperature and the ZnCl2 content. Specifically, increasing the reaction temperature led to controlled increase in the mesopore content and facilitated the formation of hierarchical porosity, which is critical to ensure efficient mass transport within porous materials. The resulting cCTFs showed high specific surface areas up to 1247 m2 g-1, and high physicochemical stability. The incorporation of ionic functional moieties to porous organic polymers improved substantially their CO2 affinity (up to 133 mg g-1, at 1 bar and 273 K) and transformed them into hierarchically porous organocatalysts for CO2 conversion. More importantly, the ionic nature of cCTFs, homogeneous charge distribution together with hierarchical porosity offered a perfect platform for the catalytic conversion of CO2 into cyclic carbonates in the presence of epoxides through an atom economy reaction in high yields and exclusive product selectivity. These results clearly demonstrate the promising aspect of incorporation of charged units into the porous organic polymers for the development of highly efficient porous organocatalysts for CO2 capture and fixation.

Electron injection from copper diimine sensitizers into TiO2: Structural effects and their implications for solar energy conversion devices

Copper(I) diimine complexes have emerged as low cost replacements for ruthenium complexes as light sensitizers and electron donors, but their shorter metal-to-ligand-charge-transfer (MLCT) states lifetimes and lability of transient Cu(II) species impede their intended functions. Two carboxylated Cu(I) bis-2,9-diphenylphenanthroline (dpp) complexes [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(COOH)2)](+) and [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(Φ-COOH)2)](+) (Φ = tolyl) with different linker lengths were synthesized in which the MLCT-state solvent quenching pathways are effectively blocked, the lifetime of the singlet MLCT state is prolonged, and the transient Cu(II) ligands are stabilized. Aiming at understanding the mechanisms of structural influence to the interfacial charge transfer in the dye-sensitized solar cell mimics, electronic and geometric structures as well as dynamics for the MLCT state of these complexes and their hybrid with TiO2 nanoparticles were investigated using optical transient spectroscopy, X-ray transient absorption spectroscopy, time-dependent density functional theory, and quantum dynamics simulations. The combined results show that these complexes exhibit strong absorption throughout the visible spectrum due to the severely flattened ground state, and a long-lived charge-separated Cu(II) has been achieved via ultrafast electron injection (<300 fs) from the (1)MLCT state into TiO2 nanoparticles. The results also indicate that the TiO2-phen distance in these systems does not have significant effect on the efficiency of the interfacial electron-transfer process. The mechanisms for electron transfer in these systems are discussed and used to develop new strategies in optimizing copper(I) diimine complexes in solar energy conversion devices.

Ordered supramolecular gels based on graphene oxide and tetracationic cyclophanes.

A new strategy to form ordered hierarchical supramolecular gels that incorporate graphene oxide (GO) sheets and cationic rigid macrocyles under mild conditions via self-assembly is demonstrated. These ordered gels are stabilized by a series of non-covalent - donor-acceptor, π-π stacking, cation-π - interactions. These theoretical studies indicate that cationic macrocycles are positioned in between GO layers with a substantial binding energy.

Redox-controlled selective docking in a [2]catenane host.

The docking by neutral and charged guests selectively in two geometrically different binding pockets in a dynamic [2]catenane host is demonstrated in the solid state by manipulating its redox chemistry. The change in redox properties, not only alters the affinity of the host toward neutral and charged guests, but it also induces a profound change in the geometry of the host to accommodate them. X-ray crystallography, performed on the two different 1:1 complexes, demonstrates unambiguously the fact that the [2]catenane host provides a uniquely different binding pocket wherein a methyl viologen dication is stabilized by interacting with a bipyridinium radical cation, despite the presence of Coulombic repulsions.

Systematic Investigation of the Effect of Polymerization Routes on the Gas‐Sorption Properties of Nanoporous Azobenzene Polymers

Functional-group-oriented polymerization strategies have contributed significantly to the initial development of porous polymers and have led to the utilization of several well-known organic transformations in the synthesis of these polymers. Because there are multiple polymerization routes that can be used to introduce the same chemical functionality, it is very important to demonstrate the effect of different polymerization routes on the gas-sorption properties of these chemically similar polymers. Herein, we have studied the rich chemistry of azobenzenes and synthesized four chemically similar nanoporous azobenzene polymers (NABs) with surface areas of up to 1021 m(2)  g(-1) . The polymerization routes have a significant impact on the pore-size distributions of the NABs, which directly affects the temperature dependence of the CO2 /N2 selectivity. A pore-width maximum of 6-8 Å, narrow pore-size distribution, and small particle size (20-30 nm) were very critical for high CO2 /N2 selectivity and N2 phobicity, which is associated with azo linkages and realized at warm temperatures. Our findings collectively suggest that an investigation of different polymerization routes for the same chemical functionalization is critical to understand fully the combined effect of textural properties, local environment, and chemical functionalization on the gas-sorption properties of nanoporous polymers.

Nanostructured ZnO as a structural template for the growth of ZIF-8 with tunable hierarchical porosity for CO2 conversion

We report a new approach to introduce hierarchical porosity into ZIF-8 by using three-dimensional nanostructured porous ZnO as a structural template. Importantly, the textural properties of these nanostructures can be tuned simply by varying the size of the polymeric templates used for the preparation of ZnO. Moreover, the growth of ZIF-8 crystals on ZnO and the resulting hierarchical porosity enabled enhanced catalytic activity for the conversion of CO2 into cyclic carbonates through an atom economy reaction in high yields with exceptional product selectivity.

Bottom-up synthesis of fully sp2 hybridized three-dimensional microporous graphitic frameworks as metal-free catalysts

We report on the bottom-up synthesis of a fully sp2-hybridized nitrogenated three-dimensional microporous graphitic framework (3D-MGF) starting from a highly preorganized, saddle-shaped tetraphenylene derivative under ionothermal reaction conditions. The 3D-MGF showed high stability and a surface area of 928 m2 g−1 along with a narrow pore size distribution. Our approach enabled template-free inclusion of the third dimension into the graphitic frameworks while retaining π-conjugation and conductivity, which was verified by their activity as metal-free electrocatalysts for the hydrogen evolution reaction.

Diazapyrenium-based porous cationic polymers for colorimetric amine sensing and capture from CO2 scrubbing conditions

We have demonstrated that solution-state properties of a diazapyrenium dication, that is to form supramolecular adducts with aliphatic amines, can be transferred into the solid-state in the form of porous cationic polymers incorporating diazapyrenium units for visual detection and capture of aliphatic amines with uptake capacities up to 31 wt% for primary amines from CO2 scrubbing systems.

Energy Band-Gap Engineering of Conjugated Microporous Polymers via Acidity-Dependent in Situ Cyclization

Conjugated microporous polymers (CMPs) offer a unique structure integrating π-conjugated backbone into a porous network for the simultaneous transport of charges and materials. However, tuning electronic properties of CMPs so far has been limited to an approach of varying the monomers, and the precious metal catalysts are inevitably needed for the C-C coupling reaction. Here, we present a powerful strategy to synthesize CMPs and precisely tune their optical band gap and surface area through metal-free in situ cyclization reaction controlled by the acid strength of acid catalysts. Notably, the optical band gap of CMPs showed a linear relationship with the p Ka of acid catalysts, which provides us with the ability to obtain the desired band gap between 2.07 and 3.35 eV, falling in the range of the visible solar spectrum. Moreover, CMPs exhibited excellent textural properties such as microporosity and high specific surface area.