Picosecond time-resolved fluorescence spectroscopy of hematoporphyrin derivative

The picosecond time-resolved fluorescence decays
I(t)
and spectra
I(\lambda, t)
for hematoporphyrin derivative (HPD) in a phosphate buffer saline aqueous solution at different concentrations (
8.4 \times 10^{-6}\sim 8.4 \times 10^{-3}
M) are measured by a two-dimensional synchroscan streak camera with a mode-locked CW dye laser, and a new emission band (which we call the
Y
-band) is found at high concentration. It is shown that the fluorescence decays composed of fast and slow components at high concentration are due to the
Y
-band (120 ps lifetime) from head-to-tail aggregates including equilibrium dimer and stable dimer, and the usual band (3.6 ns lifetime) from monomer, respectively, and the latter band is dynamically quenched by the Förster type resonance energy transfer from the monomer to the aggregate. Furthermore, the measurement of static fluorescence spectra from human gastric cancers and the surrounding in vivo after HPD injection shows that a band corresponding to the
Y
-band from the aggregate appears at only the cancerous cells.