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A Fluorescence Study of Hematoporphyrin

Volume 27, Number 6 (Dec. 1973) Page 444-449

Srivastava, R.C.; Anand, V.D.; Carper, W.R.

The fluorescence characteristics of hematoporphyrin have been studied at 26°C as a function of concentration and pH. The pk values are 4.7 and 8.2 as determined in water and water-ethanol mixtures. The fluorescence spectrum consists of a peak at 625 nm and a second, less intense band at 675 nm. These emission bands are assigned to the Qy (0 → 0) and Qx (0 → 0) states. The four absorption bands in the visible region are assigned to π → π* transitions as follows; 502 nm, (1 ← 0); 536 nm, Qy (0 ← 0); 557 nm, Qx (1 ← 0); and 605 nm, Qx (0 ← 0). Corresponding excitation wavelengths include 505, 540, 570, and 620 nm. Polarized fluorescence is used to establish molecular association as a function of concentration. The polarization factor is used to verify the change from D2h to D4h symmetry as a function of pH.