Photobleaching of the photosensitizers octa-<alpha>-butyloxy-zincphthalocyanine and 132-hydroxy-bacteriopheophorbide-a-methylester

K. Giering; Cathrin Dressler; Ralf Herter; Rainier G. Senz; Joerg G. Moser; Hans-Peter Berlien

doi:10.1117/12.230966

31 January 1996 Photobleaching of the photosensitizers octa-<alpha>-butyloxy-zincphthalocyanine and 132-hydroxy-bacteriopheophorbide-a-methylester

K. Giering, Cathrin Dressler, Ralf Herter, Rainier G. Senz, Joerg G. Moser, Hans-Peter Berlien

Author Affiliations +

Proceedings Volume 2625, Photochemotherapy: Photodynamic Therapy and Other Modalities; (1996) https://doi.org/10.1117/12.230966
Event: BiOS Europe '95, 1995, Barcelona, Spain

Abstract

The two photosensitizers Octa-(alpha) -Butyloxy-Zincphthalocyanine and 13²-Hydroxy- Bacteriopheophorbide-a-methylester with the maxima of absorption at wavelengths 735 nm and 750 nm, respectively, are promising candidates for photodynamic therapy (PDT). Photobleaching of these dyes was investigated with a pulsed Titan:Sapphire laser (duration of the pulse: 5 microseconds, repetition rate: 4 Hz) at 750 nm. Different concentrations of the dyes, in each case dissolved in ethanol, were irradiated with this laser. The variation of the bleaching rate (eta) with the total number of pulses at constant irradiation energy per pulse (alteration of the irradiation time at constant pulse duration and repetition rate) as well as with irradiation energy at constant total number of pulses was investigated. The degree of laser- induced bleaching was determined by the decrease of absorption after irradiation. A nearly linear increase of the bleaching rate with the energy per pulse was found for Octa-(alpha) - Butyloxy-Zincphthalocyanine. For 13²-Hydroxy-Bacteriopheophorbide-a-methylester at higher concentrations the bleaching rate was smaller (in comparison to Octa-(alpha) - Butyloxy-Zincphthalocyanine) with increasing sensitizer concentration at the same energies. The increase of bleaching rate with energy was approximately linear, again. No saturation effects occurred. The influence of the total number of pulses on the bleaching rate was investigated for Octa-(alpha) -Butyloxy-Zincphthalocyanine at the highest concentration. With longer irradiation times a saturation was observed. No new maxima in the absorption spectrum (monitored region 200 nm less than or equal to lambda less than or equal to 1100 nm) were found after irradiation; so the fragments of the dyes have probably no photoactivity in this range.

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K. Giering, Cathrin Dressler, Ralf Herter, Rainier G. Senz, Joerg G. Moser, and Hans-Peter Berlien "Photobleaching of the photosensitizers octa-<alpha>-butyloxy-zincphthalocyanine and 132-hydroxy-bacteriopheophorbide-a-methylester", Proc. SPIE 2625, Photochemotherapy: Photodynamic Therapy and Other Modalities, (31 January 1996); https://doi.org/10.1117/12.230966

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