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LASERS IN MEDICINE
Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine
M. E. Bashtanov,
N. N. Drozdova,
A. A. Krasnovskii (jr.) A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow
Abstract:
An investigation was made of the ratios of the intensity
$I_{df}$ of the singlet-oxygen(
$^1O_2$)-sensitised delayed fluorescence of the zinc complex of tetra(4-
tert-butyl)phthalocyanine (ZnTBPc), with the maximum at
$\lambda = 685$ nm, to the intensity
$I_{1270}$ of the photosensitised phosphorescence of
$^1O_2$ 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
$I_{df}^0/I_{1270}^0$ 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 $\alpha =(I_{df}^0/I_{1270}^0)k_r/(\gamma_f[^1O_2]_0$[ZnTBPc]), where [
$^1O_2]_0$ is the zero-time concentration of
$^1O_2$ after a laser shot;
$k_r$ is the rate constant of radiative deactivation of
$^1O_2$ 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
$\sim 2 \times 10^{11}$ M
$^{-2}$ s
$^{-1}$.
PACS:
78.55.Bq, 78.47.+p,
42.62.Fi Received: 26.05.1999
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