Monomers and Conjugated Polymers
ATOMSEL Research Group is focused on the desing and synthesis of novel functional monomers. The preparation of such monomers bearing various salient properties is one of the most useful ways to obtain conjugated polymers with desirable properties (electronic, optical, conductivity, etc.). Of particular interest are hybrid materials, a vibrant class of conjugated polymers, since the properties (low cost, processability, multi-colors with the same material, high stability and long cycle life) of different compounds could be combined in one compound. Recently, we have initiated a program aimed at atomistic band gap and electrochromic engineering of new photo and electroactive hybrid materials.
Conjugated polymers have the ability of changing their optical properties (color) as persistent and reversible response by the application of a voltage pulse. Conjugated polymers continue to fascinate many scientists due to their several advantages; e.g., low cost, processability, high optical contrast ratio, multi-colors with the same material, high stability and long cycle life with low response time. Our research group deals with the construction and the development of optical devices and displays.
Electrochromic materials have the ability of changing their optical properties as persistent and reversible response by the application of a voltage pulse. Despite the fact that the earliest electrochromic devices are mostly based on inorganic oxides (tungsten, iridium and nickel oxides, etc.), the use of organic compounds (viologens, phthalocyanines, buckminsterfullerene, conjugated polymers, etc.), as a next generation, has opened new avenues as well as myriad of applications such as electrochromic devices, smart windows, electrochromic mirrors, optical displays, light-emitting diodes, and camouflage materials. There are some factors that influence electrochromism: coloration efficiency, high contrast, injected/ejected charge, stability, continuously variable color intensity and structural flexibility ( the ability to easily modify the monomer’s structure to obtain desired properties).
Chemiluminescent Materials and Forensic Science
Chemiluminescent molecules are widely used in the field of analytical chemistry, luminol being one of the most prominent examples, mainly for its blood detection applications. However, incorporation of such pyridazine-based chemiluminescent probes into polymeric structures have proven to be challenging. The main problems are low solubility of these polymers, low thickness of polymeric film, and complex polymerization mechanisms. In our research group, we try to initiate a program aimed at the design and synthesis of novel chemiluminescent materials that can easily be polymerized without the destruction of the chemiluminescent unit during the polymerization process. We have envisaged that suitable chemiluminescent groups appended in monomeric to trimeric systems where both the emission of light and polymerization can be controlled by electrochemical means would make the materials amenable for use in sensors and in forensic sciences.
Chemiluminescent (CL) materials have been the subject of extensive research in the field of analytical chemistry due to their high sensitivity, high luminescence efficiency and simple instrumentation. Among these, luminol and derivatives that contain a pyridazine unit are the most attractive CL compounds and they have been used both in the analysis of food, pesticide, air pollution and for the detection of H2O2, biologically active compounds (e.g. glucose, adenine, folic acid, lactic acid, dopamine, glycolic acid), immunoassay and DNA probe assays. Additionally, investigators in forensic science used luminol effectively to detect trace amounts of blood left at crime scenes, since Fe3+ ions in blood samples catalyze the CL reaction and a visible blue-green light (at 425–450 nm) can be easily seen with naked eyes in the dark, if there are any bloodstains.
The electrochromic devices were constructed using electrochromic polymers coated on ITO separated by gel electrolyte from each other and have the ability of changing their optical properties as persistent and reversible response by the application of a voltage pulse. Gel electrolyte was prepared using tetrabutylammonium salts, acetonitrile, PMMA, and propylene carbonate. The electro-optical properties of the device were recorded in-situ under various applied potentials. Finally, square wave potential method was used to perform switching between the two colored states (reference and counter electrodes shorted together).
An ideal electrochromic device should switch between its different oxidation states with a certain response time and it should also be stable upon multiple switching. The charge passed at 95% of the full optical switch is selected to evaluate response time and the optical contrast since the color change has taken place mostly at that level and the last 5% of the color change is difficult to perceive with the naked eye. Another important parameter in the electrochromic device is the long cycle life.Coloration efficiency (CE) is a useful term for measuring the power efficiency of the electrochromic devices and can be calculated via optical density using the following equations;
where Qd is the injected/ejected charge during a redox step; Tcolored and Tbleached are the transmittance in the oxidized and neutral states, respectively.