Investigation of Ground- and Excited-State Photophysical Properties of 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin with Ruthenium Outlying Complexes

The present work employs a set of complementary techniques to investigate the influence of outlying Ru(II) groups on the ground- and excited-state photophysical properties of free-base tetrapyridyl porphyrin (H(2)TPyP). Single pulse and, pulse train Z-scan techniques used M association with laser flash photolysis, absorbance and fluorescence spectroscopy, and fluorescence decay measurements, allowed us to conclude that the presence of outlying Ru(II) groups causes significant changes on both electronic structure and vibrational properties of porphyrin. Such modifications take place mainly due to the activation of. nonradiative decay channels responsible for the emission, quenching, as well as by favoring some vibrational modes in the light absorption process, It is also observed that, differently from what happens when the Ru(II) is placed at the center of the macrocycle, the peripheral groups cause an increase of the intersystem crossing processes, probably due to the structural distortion of the ring that implies a worse spin orbit coupling, responsible for the intersystem crossing mechanism.

Previous illumination of a water soluble chlorine photosensitizer increases its cytotoxicity

Photodithazine (PDZ) is an N-methyl-D-glucosamine derivative of chlorine e6 that is water soluble and has an intense absorption in the range of 650-680 nm. PDZ photobleaching and photoproduct formation were induced by illumination with laser at two wavelengths: 514 nm (ion argon laser) as well as in 630 nm (dye laser). The time constants of PDZ photobleaching were: 18 min for 630 nm irradiation and 50 min for 514 nm irradiation, suggesting that degradation after irradiation with red light is faster than with green light. Photoproducts formation was evidenced by the appearance of a new absorption band at 668 nm with slight broaden of the Soret band, suggesting that there was no break of the macrocycle. The cytotoxicity of the photodegradated PDZ was investigated and showed to be lower in the dark and higher than non irradiated PDZ. These results may have important clinical implications for PDT such as the possibility to use the previously irradiated PDZ just before clinical application in order to get increased efficiency.