Near-infrared phosphorescent metalloporphyrins

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Abstract
In the near infrared range fluorescent background signals are very small and it is possible to reach high sensitivity in the detection of labeled compounds. With phosphorescent compounds as labels, it is possible, firstly, to add microsecond temporal resolution for background rejection for NIR labels and thus to improve sensitivity. Secondly, compounds that are phosphorescent in NIR are very promising for oxygen life-time imaging of living tissue. Several different groups of palladium and zinc porphyrins and phthalocyanins (meso-tetraphenyl)-(tetrabezo)-porphyrin, meso-tetraphenyl-(tetranaphtho)-porphyrin, tetraazaporphyrins, phthalocyanines) which possess strong absorbance in NIR range were synthesized and analyzed for room temperature phosphorescent properties in organic solvents and in water solution. Among them only Pd- tetrabenzo-(tetraphenyl) porphyrins have high quantum efficiency (10%) with the life-time 328 us and excitation 630 nm, emission 800 nm. In the NIR spectral range water strongly quenches the long-lived phosphorescence of metalloporphyrins. Metalloporphyrins can form inclusion complex with cyclodextrines in which water quenching is almost eliminated. Quantum efficiency and life-time in cyclodextrin solutions are the same as in organic solvents. We analyzed the influence of three different cyclodextrines (alfa, beta and gamma) on the phosphorescent properties of Pd-porphyrins and highest enhancement of the phosphorescence signal occurred for hydroxypropilated (Beta) -cyclodextrin.

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