Fluorescent materials are widely used in a variety of medical diagnostic tests, such as immunoassays. Test sensitivity relies upon the ratio of material's fluorescent intensity and background signals. The significant overlap of biological substrate autofluorescence and fluorescence from commercially available probes dramatically compromises detection sensitivity. Commercially available probes also require UV or near-UV light excitation, causing severe degradation of biological substrates. Certain lanthanide ions, such as ytterbium (III) with emission at 980 nm, are good candidates to overcome these shortcomings. Emission is usually realized by an indirect sensitization process,  in which energy from the excited state (usually a triplet state) of a sensitizer transfers to the excited states of lanthanide ion and emits in the NIR region when it relaxes to the ground state. Sensitizers thus play significant roles in producing strong NIR emission for medical diagnosis. Over the last two decades, numerous NIR emitting lanthanide-based probes with different sensitizers have been synthesized and their sensitization capability for NIR emission of lanthanide examined. These materials exhibit poor emission efficiency and require short wavelength excitation, both undesirable for biomedical applications. To this end, new porphyrin sensitizers with bind groups (8-hydroxylquinoline and dipicolinic acid) conjugated to porphyrin rings through a triple bond were synthesized. These porphyrins exhibited good solubility in alcoholic solvents, and strong absorption in the red light region (600 to 750 nm). Upon addition of the porphyrin solution to an ethanol solution of ytterbium (III) ion, characteristic emission at 980 nm from ytterbium (III) was observed under 650 nm light excitation, which showed great potential for medical diagnostic tests. In this presentation, synthesis, characterization, density functional theory calculations, and photophysical studies will be discussed.

Novel green porphyrins as long wavelength sensitizers for near-infrared emission of  ytterbium (III)

246th National Meeting (2013)

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