Аннотация:Porphyrin molecules have a highly conjugated cyclic structure and are theorized to have unusually large two-photon absorptivities (σTPA), i.e., σTPA∼102GM. The authors tested this claim. Ultrafast two-photon absorption (TPA) spectroscopy was performed on solutions of hemoglobin, which contains a naturally occurring metaloporphyrin. They used a pump-probe technique to directly detect the change in transmission induced by TPA over the wavelength range of λ0=780–880nm. As controls, they measured the TPA of the dyes rhodamine 6G and B; their measurements both verify and extend previously reported values. In new results, hemoglobin was found to have a peak two-photon absorptivity of σTPA∼150GM at λ0=825nm, near a resonance of the Soret band. This value supports theoretical expectations. They also found a significant difference in the TPA of carboxyhemoglobin versus oxyhemoglobin, e.g., σTPA=61GM versus σTPA=18GM, respectively, at λ0=850nm, which shows that the ligand affects the electronic states involved in TPA.
