M. Deniz Yilmaz

A Panchromatic Boradiazaindacene (BODIPY) Sensitizer for Dye-Sensitized Solar Cells

A novel distyryl-substituted boradiazaindacene (BODIPY) dye displays interesting properties as a sensitizer in DSSC systems, opening the way to further exploration of structure-efficiency correlation within this class of dyes.

A monostyryl-boradiazaindacene (BODIPY) derivative as colorimetric and fluorescent probe for cyanide ions.

We developed a novel boradiazaindacene derivative to detect cyanide ions in solution at micromolar concentrations. This structurally simple chemosensor displays a large decrease in emission intensity and a reversible color change from red to blue on contact with cyanide ions. Highly fluorescent polymeric films can be obtained by doping with the chemosensor. Such polymeric materials can be used for the sensing of the cyanide ions in polymer matrices.

Janus Particles with Controllable Patchiness and Their Chemical Functionalization and Supramolecular Assembly

Seeing the right face: Mono- and bifunctionalized Janus particles with controllable chemical patchiness are prepared by a general masking/unmasking technique and subsequent chemical functionalization (see picture). Supramolecular host- and guest-functionalized Janus particles were prepared, and specific noncovalent host-guest interactions were used to controllably assemble heterogeneous particles.

Ratiometric Fluorescent Detection of an Anthrax Biomarker at Molecular Printboards

Anthrax is an acute disease, concurrently a potential biological warfare agent caused by Bacillus Anthracis. The accurate, rapid, sensitive, and selective detection of Bacillus spores plays a vital role in order to prevent a biological attack or outbreak of disease. Bacterial spores contain a main core cell which is enclosed by protective layers. As a major component of these protective layers, bacterial spores contain up to 1 M dipicolinic acid (DPA), accounting for 5−15 % of the dry mass of the bacterial spore. Hence, DPA is a convenient biomarker for these spores. In recent years a number of biological and chemical detection methods for Bacillus Anthracis spores have been investigated. Biological methods are based on polymerase chain reactions and immunoassays. Important chemical methods employ vibrational spectroscopy (FT-IR, Raman and SERS) and photoluminescence. Among them, lanthanide (Ln3+)-based luminescent detection of DPA has been most promising owing to the unique photophysical properties of Ln3+-DPA chelates, including their bright luminescence upon sensitization by DPA, the long luminescence lifetimes compared to free Ln3+, and the concomitantly high luminescence enhancement ratio upon coordination of DPA to the Ln3+ center. Besides the use of DPA itself as a sensitizer, ratiometric fluorescent detection of anthrax spores can be achieved through the displacement of a different sensitizer by DPA.

Probing Multivalent Interactions in a Synthetic Host–Guest Complex by Dynamic Force Spectroscopy

Multivalency is present in many biological and synthetic systems. Successful application of multivalency depends on a correct understanding of the thermodynamics and kinetics of this phenomenon. In this Article, we address the stability and strength of multivalent bonds with force spectroscopy techniques employing a synthetic adamantane/β-cyclodextrin model system. Comparing the experimental findings to theoretical predictions for the rupture force and the kinetic off-rate, we find that when the valency of the complex is increased from mono- to di- to trivalent, there is a transition from quasi-equilibrium, with a constant rupture force of 99 pN, to a kinetically dependent state, with loading-rate-dependent rupture forces from 140 to 184 pN (divalent) and 175 to 210 pN (trivalent). Additional binding geometries, parallel monovalent ruptures, single-bound divalent ruptures, and single- and double-bound trivalent ruptures are identified. The experimental kinetic off-rates of the multivalent complexes show that the stability of the complexes is significantly enhanced with the number of bonds, in agreement with the predictions of a noncooperative multivalent model.

Convergent synthesis and light harvesting properties of dendritic boradiazaindacene (BODIPY) appended perylenediimide dyes

A convergent synthesis methodology, together with “click-chemistry” between azides and terminal alkynes, allows straighforward access to dendritic light harvesting systems. The novel dendrimer reported in this study has eight boradiazaindacene (BODIPY) units at the periphery and a perylenediimide (PDI) dye at the core. We have demonstrated that visible light is effectively collected as a result of the large absorption cross section of the dendrimer and efficiently channeled to the core PDI unit, resulting in a significant antenna effect. While being one of the very few energy transfer systems with a BODIPY and PDI chromophore pair, this novel dendritic molecule is one of the most efficient in light harvesting. The factors that may play important roles as the generation number increases also become apparent when emission characteristics were analyzed in comparison with a lower generation dendrimer.

Local doping of silicon using nanoimprint lithography and molecular monolayers.

Micrometer-scale monolayer patterns of a phosphorus-containing molecular precursor are fabricated on nearly intrinsic Si(100) using nanoimprint lithography. The patterned sample is protected by a SiO2capping layer applied by electron beam evaporation and subjected to rapid thermal annealing (RTA) to diffuse the phosphorus dopant atoms into the bulk silicon locally.

Expression of Sensitized Eu3+ Luminescence at a Multivalent Interface

Assembly of a mixture of guest-functionalized antenna and Eu(3+)-complexed ligand molecules in a patterned fashion onto a receptor surface provides efficient localized sensitized emission. Coordination of a carboxylate group of the antenna to the Eu(3+) center and noncovalent anchoring of both components to the receptor surface appeared to be prerequisites for efficient energy transfer. A Job plot at the surface confirmed that coordination of the antenna to the Eu(3+) center occurs in a 1:1 fashion. The efficiency of this intramolecular binding process is promoted by the high effective concentration of both complementary moieties at the surface. The system constitutes therefore an example of supramolecular expression of a complex consisting of several different building blocks which signals its own correct formation.

Nonlinear Amplification of a Supramolecular Complex at a Multivalent Interface

Competition with a monovalent cyclodextrin host (blue cones) in solution drives the multivalent binding of a Eu(3+) complex and a sensitizer molecule to cyclodextrin monolayers through a nonlinear self-assembly process. Adamantyl groups (light-blue spheres) are attached to the EDTA ligand (black) and the antenna molecule (orange), which has a carboxylate group for coordination to the Eu(3+) ion (yellow or red in free or complexed form, respectively).

Electrochemical stability of self-assembled alkylphosphate monolayers on conducting metal oxides.

Alkylphosphate self-assembled monolayers (SAMs) were prepared on Nb-doped SrTiO(3) (Nb-STO) conducting metal oxide substrates. Unlike thiols on gold, the alkylphosphate SAMs on Nb-STO exhibited an electrochemical stability over a wide voltage range from -2 to 2 V. Cyclic voltammetry showed that the SAM modification inhibited the electrochemical activity of the underlying conducting substrate with an efficiency dependent on the chain length. Impedance spectroscopy showed that SAM-modified Nb-STO substrates have a significantly higher resistance than bare substrates.