Aggregation effect of Thiazine dyes over Singlet Oxygen quantum yield

VARA J Y ORTIZ CS.

Congreso; Tercera Reunión Internacional de Ciencias Farmacéuticas; 2014

Aggregation effect of Thiazine dyes over Singlet Oxygen quantum yield Keywords: Photosensitizer; Azure B; monobrominated Azure B; photochemical reactivity Thiazine dyes are used for coloring substrates in biological and medical studies and are promising compounds for photosensitizing applications. Recent identification, in our laboratory, of the monomeric species of these dyes showed that the monomer described in literature corresponds to different dimers. Due to the aggregation of photosensitizers reduces the production of singlet oxygen (1O2), the objective of this study was to evaluate the 1O2 quantum yield (ΦΔ) of the monomeric and dimeric species of two Thiazines: Azure B (AzB) and monobrominated Azure B (AzBBr). Phosphorescence decay of 1O2 and photooxidation of 9,10-dimethylanthracene (DMA) were used as methodology. Monomeric and dimeric forms were analyzed in N,N-dimethylformamide (DMF) and Methanol (MeOH) employing Rose Bengal (RB) and Methylene Blue (MB) as references. Monomeric species of AzBBr and AzB presented high Φ by luminescence (1.0 and 0.72, respectively) and low values by photooxidation of DMA (0.09 and 0.29, respectively). Moreover, the dimeric species showed similar values of Φ by both methodologies (AzBBr: 0.7 and AzB: 0.3, approximately). Furthermore, the bromination increased Φof the compound. To understand the differences obtained, scavenging effect of AzBBr monomer was evaluated by photooxidation of DMA using RB as photosensitizer. These results indicated that AzBBr monomer could act as physical quencher due to Φ decreased 20% in presence of the dye. This behavior could be associated to the presence of NN-dimethylaniline moiety as part of its chemical structure. In addition, dimeric species of AzBBr and AzB presented high Φ because the aromatic amine is involving in different interaction forces that stabilize their aggregates. For this reason, the amines could be less available for the formation of exciplex with 1O2 which trigger the deactivation of excited molecule. The dimers of AzB and AzBBr will be the optimal photosensitizers, due to these species presented highest Φthan its respective monomer.