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Published online by Cambridge University Press: 01 February 2011
Strong enhancement of the two photon absorption (TPA) cross section at 812 nm is observed for tetrakis(4-sulphonatophenyl)porphyrin diacid (H4TPPS2-) when a J-type aggregate is formed in water, in comparison to the one observed for the H4TPPS2- monomer in mixture of water, DMSO and urea. Open aperture Z-scan experiments, performed with ultra-short laser pulses, are employed to measure the TPA absorption cross section. The observed enhancement is discussed in terms of possible electronic cooperative effects in the aggregate.