A New Method for the Synthesis of Bromine-Containing Heterocyclic Compounds for Photovoltaic Polymers

With the development and improvement of systems for converting sunlight into electric and thermal energy, more and more work is emerging on the development of the newest and most promising direction in solar energy, namely the creation of solar cells based on photosensitive polymers. Recently the power conversion efficiency of organic photovoltaic (OPV) devices has overcome the barrier of 17%, and thus we can expect a new wave of scientific interest in the development of new, more efficient OPV devices. Unfortunately, during searching for highly efficient chemical structures of OPV polymers, the researchers missed an important point: all photovoltaic polymers consist of aromatic and heteroaromatic «building blocks», which, in turn, are synthesized based on outdated techniques using highly toxic, dangerous for life and environment precursors. The development of «green», environmentally friendly, economically viable methods for the synthesis of photovoltaic polymers and building blocks for their production, will make the energy obtained from OPV truly «green». In this work, we present an alternative, «green» method for synthesizing halogen-containing aromatic and heteroaromatic, expensive building blocks most commonly used in the synthesis of photovoltaic polymers, which can be used to obtain photovoltaic polymers of various structures. We present the original methods for the synthesis of 4,4-dibromo-1,1- biphenyl (1), 4,7-dibromo-2,1,3-benzothiadiazole (2), 2-bromothiophene (3) and 2,5-dibromothiophene (4). All these methods differ from the previously described routes by their simplicity and convenience of their implementation, the absence of corrosive and irritant reagents, good yield and compliance with the principles of «Green Chemistry».

KINETIC'S INVESTIGATION OF METHACRYLIC MONOMERS BASED ON 2-STYRYLQUINOLINE

Polymethylmethacrylate is widely use material in optics due to its atmosphere resistance, chemical stability, good mechanical properties, transparency and light transmission. Due to these properties, PMMA is often used as a polymeric matrix for creating photosensitive polymers and polymers with nonlinear optical (NLO) properties. Materials with NLO properties can be made by introducing moleculas of chromophores into the polymer chain. There are two fundamentally different ways of doing this. The first is to create composite material where the chromophore is a dispersed phase and is introduced into the system as a "guest". In the second case, the chromophore is introduced into the polymer chain covalently, and can be included in the side and the main chain. Studies of polymers containing NLO chromophore in the side chain have shown a number of advantages: better orientation of the chromophores under the action of an electric field; relaxation processes are much slower; increasing time and thermal stability; increasing the glass transition temperature of the polymer. Based on present knowledge we decided to design new methacrylic polymers with styrylquinoline chromophore in side chain. The polymerization ability of the new monomers for free radical homopolymerization was investigated kinetically by using dilatometric method. It was found that new 2-styrylquinoline containing monomers are able to homopolymerization with high conversions (63–83%). The polymerization was carried out in DMF using 2,2´-azobisisobutyronitrile as initiator at 80°C in argon atmosphere. The products of polymerization were characterized by 1H NMR spectroscopy. It was installed that all new monomers have bigger speed of polymerization (Ksum= 1.36–8.33×103 l/mol×s) then methylmethacrylate (Ksum= 0.5×103 l/mol×s), phenylmethacrylate (Ksum= 1.1×103 l/mol×s) and similar to polymerization of 2-methyl-8-oxyquinoline methacrylate (Ksum= 3.28×103 l/mol×s). It was found that speed of polymerization increases with increasing electron donating power of substitute in paraposition of the aromatic ring. It has been proven that presence of electron acceptor group reduces speed of polymerization.

Holographic laser processing for three-dimensional photonic lattices

This article describes a holographic laser-processing method for independently controlling the lattice symmetry and lattice constant in three-dimensional photonic lattices. With this approach, optical periodicity is created in lower dimensions and three-dimensional periodicity is obtained by a combination of several lower-dimensional periodic structures. The proposed holographic laser-processing method is compared with the standard four-beam technique. Examples of experimental demonstration achieved in photosensitive polymers are given. The article also introduces a multiphoton direct-writing technique for creating defect structures in lattices towards production of defect cavity-functionalized photonic crystal devices. It shows that all Bravais lattices can be produced by choosing proper incident vectors of laser beams. The lattice constant of the structure can be changed without distorting its lattice symmetry and lattice elements.