A Fluorescence Study of Hematoporphyrin

Abstract

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 Q_x (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 D_2h to D_4h symmetry as a function of pH.