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Hydroporphyrin Photonics Materials as Activatable Singlet Oxygen Photosensitizers – Kalen Sullivan

The study of novel hydroporphyrin photonics materials is a field which has yet to be explored despite potential to yield a variety of multidisciplinary applications. The goal of this research is to understand the photophysical properties of a new class of hydroporphyrins and establish their feasibility as activatable singlet oxygen photosensitizers and phosphorescent probes. This research combines the synthesis novel organoplatinum hydroporphyrin derivatives with the examination of the photophysics of new hydroporphyrin derivatives, which ultimately provides an understanding of the structure-photophysical relationship in these materials.


Four pyrrolic rings connected by a methylene linkage constitute the class of bioorganic molecules known as tetrapyrrolic macrocycles. Varying the degree of saturation at one or more of the pyrrolic rings establishes the macrocyclic sub-classes shown below.



Figure 1. Generic molecular structures of unsubstituted tetrapyrrolic macrocycles. Hydroporphyrins are chlorin and bacteriochlorin.





Scheme 1. Organic synthesis of novel hydroporphyrin platinum complex.



The influence of platinum on the electronic structure of the bacteriochlorin allows for a higher probability of intersystem crossing into the triplet state, potentially increasing the production of reactive singlet oxygen species (1O2). This research will provide the basis for the development of materials with improved singlet oxygen generation and phosphorescence that will be very beneficial for photodynamic therapy in targeted tumor cells. Because bacteriochlorins absorb light in the deep red, near- IR spectral windows (650 – 1350 nm), these molecules will absorb light at maximum depths in biological tissue. This permits potential applications in fluorescence sensing and imaging for medicinal diagnosis, photodynamic therapy, and in vivo imaging studies.



REU student Kalen Sullivan (center) with graduate student mentor Nopondo Esemoto (left) and faculty mentor Prof. Marcin Ptaszek (right) in Prof. Ptaszek organic synthesis laboratory



Our research this summer proposes that upon introduction of a heavy metal atom such as platinum (Pt), the photophysics of the bacteriochlorin will change due to the heavy atom effect. Photophysical properties such as absorption, emission, quantum yield, and fluorescence lifetime will be determined.