Laser induced singlet-oxygen-sensitised delayed fluorescence of dyes in aqueous solutions

It is shown that water-soluble derivatives of phthalocyanines – poly(diethoxyphosphinylmethyl)substituted aluminium phthalocyanines – emit intense singlet-oxygen-sensitised delayed fluorescence upon laser-induced formation of singlet oxygen in air-saturated aqueous (D₂O) solutions. The delayed fluorescence is emitted by the dye molecules which accepted energy from two molecules of singlet oxygen. The quantum efficiency of delayed fluorescence in aerated D₂O of the chloroaluminium complex of octa(diethoxyphosphinylmethyl) phthalocyanine corresponds to the rate constant of population of excited dye molecules which is equal to (5.5 ± 3) × 10¹² mole^-2 L² s^-1. This value is only an order of magnitude smaller than that for tetra(4-tert.-butyl)phthalocyanine earlier studied in aerated organic solvents. It is shown that these phthalocyanine derivatives can be used as highly sensitive luminescence indicators of singlet oxygen produced in aqueous solutions of different compounds upon laser excitation.