Large two-photon absorptivity of hemoglobin in the infrared range of 780-880 nm.
Porphyrin molecules have a highly conjugated cyclic structure and are theorized to have unusually large two-photon absorptivities (sigmaTPA), i.e., sigmaTPA approximately 10(2) GM. 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 lambda0=780-880 nm. 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 sigmaTPA approximately 150 GM at lambda0=825 nm, 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., sigmaTPA=61 GM versus sigmaTPA=18 GM, respectively, at lambda0=850 nm, which shows that the ligand affects the electronic states involved in TPA.
Clay
G Omar
GO
Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
Schaffer
Chris B
CB
Kleinfeld
David
D
D003198:Computer Simulation; D036681:Fluorescence Recovery After Photobleaching / Q000379:methods*; D006454:Hemoglobins / Q000737:chemistry* / Q000528:radiation effects; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D013055:Spectrophotometry, Infrared / Q000379:methods*
D006454:Hemoglobins