Green Synthesis of Organopalladium Photosensitizers
Green chemistry is at the forefront of current developments of various research areas in chemistry. One of its major objectives is to develop efficient solvent-free and low-energy preparative methods for various classes of existing and new chemicals. The feasibility of this green-chemistry concept will be demonstrated on the synthesis of organopalladium complexes and the majority of synthetic steps in this project will be performed in the solid state by methods of accelerated aging and mechanochemistry. The first mechanosynthesis of organopalladium compounds via C-H bond activation, which is of exceptional importance in organic synthesis, by palladium(II) acetate has been recently reported by our group. Within this project we propose to develop and implement the solid-state methods for the synthesis of a series of cyclopalladated aromatic azo compounds. Interest in such complexes with conjugated C=C and N=N bonds arises from their strong absorption and emission in the low energy region, which qualifies them as good candidates for the biomolecular labels. In this regard, their affinity to target amino acids, short peptides and nucleobases will be studied by UV-vis and fluorescence spectroscopies. Consequently, an additional benefit of this project will be a series of new chromogenic and fluorogenic chemosensors. The solid-state structures of the products will be determined by X-ray diffraction, NMR, Raman and IR spectroscopies. The cyclopalladation mechanism in the solid state will be studied by in situ monitoring of the reactions using Raman spectroscopy, and in the solution by UV-vis and NMR spectroscopies along with the ESI mass spectrometry. The optical characteristics of complexes will be evaluated by UV-vis and fluorescence spectroscopies. The experimental results will be rationalized by theoretical studies in order to explain isomerism of complexes, the nature of their electronic transitions and to obtain additional support for the cyclopalladation mechanism.