Properties of the blue-shifted emission of hematoporphyrin and related derivatives in aqueous solution

A blue-shift of the emission spectrum of hematoporphyrin and of its derivatives used in tumor phototherapy is shown to occur in water solutions. After 48 h incubation at 37°C, this emission becomes predominant, particularly in derivatives with a high degree of aggregation, and is characterized by a decay time of ≈2.6 ns. The appearance of this band, which is peaked at 580 nm, can be interpreted on the basis of a binding mechanism of monomers to stable aggregates.