Pt(II) complexes with square planar geometry can be water soluble and emissive at room temperature. Metal-metal intramolecular or intermolecular interactions often influence the emission properties. The emission of some Pt(II) complexes is very sensitive to oxygen in aqueous solutions, which can be utilized for the sensing of oxygen (O2) in biological systems to probe hypoxic conditions during cancer growth and other abnormalities. The presence of oxygen drastically quenches the emission of a representative complex we investigated. In our research group, we are utilizing such complexes for the bio-imaging of worm and fish models under various degrees of hypoxic conditions.  Stability in aqueous water, however, is rather limited and the representative complex starts decomposition within a day at room temperature. To overcome this stability problem in aqueous systems at room temperature, we have incorporated the Pt(II) complex into the polymer matrix of polyacrylonitrile (PAN) in order to increase its long-term stability. Incorporation of the Pt(II) complex within PAN leads to the formation of phosphorescent microspheres with diameter in the 0.1-1 micron regime according to dynamic light scattering and fluorescence microscopy. Presence of this polymer exceptionally enhanced the stability of the Pt(II) complex in aqueous suspension at room temperature without compromising the photophysical properties in terms of band energy. All compositions and sample variations examined were exceptionally stable at room temperature for more than 2 years.  These polymeric microspheres have significantly enhanced the luminescence intensity, lifetime, and quantum yields compared to the native Pt(II) complex in water, which was limited to minutes spetroscopically and hours visually in the absence of polymers. The resulting hybrid polymeric/molecular phosphorescent microspheres exhibit lower oxygen sensitivity and enhanced thermal stability vs. the dissociated components. The phosphorescent microspheres' particles size can be tuned with temperature and relative or absolute concentration of the two components.  The so formed phosphorescent microspheres are promising candidates for both biological and environmental applications including protein labeling, bio-imaging and sensing applications.

Synthesis, characterization, and photophysical studies of exceptionally stable phosphorescence polymeric microspheres with Pt(II) complexes for biomedical applications

247th National Meeting (2014)

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