Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine

An investigation was made of the ratios of the intensity I-df of the singlet-oxygen(O-1(2))-sensitised delayed fluorescence of the zinc complex of tetra(tert-butyl)phthalocyanine (ZnTBPc), with the maximum at lambda = 685 nm, to the intensity I-1270 Of the photosensitised phosphorescence of O-1(2) With the maximum at lambda = 1270 nm in deuterated benzene when excited with lambda = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25-0.7 mJ cm(-2)) and on the concentration of ZnTBPc (0.06 - 3.4 mu M), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence Id(f)(0/)I(1270)(0) varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc, The intensity I-df(0) decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient alpha = (I-df(0)/I-1270(0))k(r)/(gamma(f)[O-1(2)](0)[ZnTBPc]), where [O-1(2)](0) is the zero-time concentration of O-1(2) after a laser shot; k(r) is the rate constant of radiative deactivation of O-1(2) in the investigated solvent; gamma(f) is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was similar to 2 x 10(11) M-2 s(-1).