Skene Group - Groupe Skene

Research

Overview

We are interested in new classes of material that are suitable for opto/electronic applications. Our research relates to the synthesis and the characterization of new polymers with the aim of increasing the effectiveness of emission and higher turn-over rates.  We are also interested in the preparation and characterization of new functional materials derived from azomethines connections. By incorporating different aryl units using these easy connections, we are examining the effect of these groups upon the photophysical, electrochemical, opto-electronic, and crystallographic properties by establishing structure-property relationships. Not only are we concerned with the  fundamental excited state deactivation processes of these highly conjugated  materials, but we also interested in tuning the properties making these functional  materials suitable for plastic electronics.   

1) Thiophene Derivatives

We are pursuing efficient one-pot method for the preparation of novel conjugated thiophenes using azomethines (-N=C-) linkages. Given the newness of these compounds concomitant with the unprecedented photophysical and electrochemical studies, we endeavor to characterize the photophysics and electrochemistry of these compounds. We are investigating the effect of terminal electronic groups on the photophysical and electrochemical properties in order to prepare new compounds with tunable properties desired for a given application.  Additionally, we are examining the effect of electronic groups incorporated along the conjugated back-bone in order to develop compounds with tunable properties, including absorption, emission, and redox potentials.  Modulating these properties as a function of degree of conjugation is also being examined.

2) Electrochromism

We developed recently azomethine co-monomers capable of quantitative reversible radical cation.  We are further evolving our research by synthesizing new co-monomers whose normally reactive species can be tamed.  Subsequently, the long lived radical cation and reversible oxidation result in pronounced color changes both in solution and in thin films.  An example of the rapid switching times and color changes possible can be seen here.

3) Fluorene Derivatives

Fluorene exhibits high fluorescence quantum yield and is therefore the choice compound of the emitting layer in OLED. Azomethines derived fluorenes are attractive alternatives to current oligofluorenes obtained via Suzuki coupling because they are both easily prepared and purified. While only a few studies have examined fluorene azomethines, none have extensively examined the photophysics and the deactivation modes of these novel conjugated compounds. Information regarding the excited state including the triplet manifold of azomethines and knowledge of their quenching mechanism are pivotal for determining their suitability as advanced materials for functional devices. We are interested in the synthesis of fluorene and fluorenone derivatives as model compounds to examine the photophysics of these novel compounds. We are investigating the structure-photophysical property relationship of the various fluoreno azomethines to determine the quenching mechanism in hope of designing new efficient materials to be used as the emitting layers in OLEDs.

Example of anodic polymerization of a fluorene co-monomer and its crystal structure.

4) -donor and Acceptor Co-Monomers

Co-monomers contain the elements of the co-polymer structure such as a central aromatic acceptor core inserted between electron-rich donors. This configuration simplifies the polymerization process that would otherwise require two or three separate monomers to obtain analogous polymers via other coupling methods. We are interested in co-monomers consisting of electron deficient heterocycles sandwiched between electron heterocycles since they provide the means to tailor polymer properties and they benefit from intramolecular charge transfer. The -deficient heterocycles can easily be reduced and polymers derived from such co-monomers are equally n-dopable. Incorporation of external -rich units into the co-monomer affords polymers that can be both p- and n-doped. We are pursuing the synthesis of characterization of various co-monomers that can be either anodically or cathodically homo-coupled and mutually be p- and n-doped.

 
5) Controlled Polymerization of Brushes on Surfaces

Polymer brushes consisting of end-grafted polymers on surfaces are frequently used to develop smart or responsive surfaces including biocompatible surfaces for retarding the non-specific adsorption of macromolecules, nanodevices, and self-biolubricating surfaces.  We are interested in using atom transfer radical polymerization (ATRP) for examining the various parameters to control the density of the initiator grafted on silica surfaces and mica surfaces.  Controlled polymerization will afford polymer brushes of consistent lengths that can easily be hydrolyzed affording charged brushes. The effect of different cations on the mechanical properties of the surfaces will be examined. In collaboration with Prof. S. Giasson, we are investigating covalent grafting of ATRP initiators and the controlled polymerization on activated mica to afford polymers with discrete molecular weights. Mica is the choice substrate for measuring mechanical properties by Surface Forces Apparatus (SFA). Because of the challenges to characterize the grafted materials to mica, we have developed new methods allowing to measure the absolute height of the brushes. Polymer brushes of controlled/known lengths are desired to examine the effect of different cations of the surface friction between two polymer surfaces measured by SFA. Various other techniques including AFM and ellipsometry are also used to characterize the brushes polymerized from the surface.

Example of controlled polymerization on surfaces.