Cyanine induced aggregation in meso-tetrakis(4-sulfonatophenyl)porphyrin anions

The interaction of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (H4TPPS2− and H2TPPS4−) with cationic cyanines, DiOC2(3) and DiOC6(3) were studied. The cyanine with the hexyl chain, DiOC6(3) induced aggregation of the porphyrin with new absorption and emission bands. The stoichiometric ratio of porphyrin ∶ cyanine in the aggregate is ∼1 ∶ 4. UV–Vis absorption, fluorescence, fluorescence lifetime, resonance light scattering and dynamic light scattering studies were used for further characterization of the aggregate. The spectroscopic aggregation number for the porphyrin in the aggregate was estimated to be ∼2.5 by comparing the half width of its emission spectrum with that of the monomer. The spontaneous aggregation of porphyrin with DiOC6(3), but not with DiOC2(3), indicates the role of the chain length of the alkyl group attached to the benzoxazole in the cyanine dye for stabilizing the structure of the aggregate.