Novel data on the spectra of photosensitized singlet-oxygen luminescence in the solution phase: detection of vibrationally excited monomols and dye-activated dimols of singlet oxygen

The spectrum of photosensitized singlet oxygen luminescence has been investigated in air- saturated CCl4, hexafluorobenzene and freon 113 at the wavelengths shorter fundamental at (lambda) < 1200 nm. Novel bands have been detected. The 1073 nm band was observed in all solvents with all photosensitizers used. The data suggest that it accompanies the 1(Delta) g (v equals 1) yields 3(Sigma) g (v equals 0) transition in thermally activated singlet oxygen molecules. The 1160 nm band was detected in CCl4. It probably corresponded to simultaneous vibronic transitions involving singlet oxygen and Cl-atoms in solvent molecules. The spectra and intensity of luminescence in the visible region strongly depended on the chemical structure and fluorescence properties of the photosensitizers. When the main fluorescence maximum of a photosensitizer was shorter than 630 nm, the 635, 703 and 780 nm, luminescence bands corresponding to the singlet-oxygen dimols were observed. When main fluorescence maxima of photosensitizers or products of their photodestruction were at (lambda) < 700 nm, the luminescence spectra corresponded to fluorescence of photosensitizers and products of their photodestruction. The data suggest that this luminescence is emitted by singlet oxygen dimols activated in collisions with photosensitizer molecules and by molecules of the photosensitizers and products of their destruction excited as a result of energy migration from singlet oxygen dimols. Some photosensitizers as metal-free tetra-4-tret-butyl-phthalocyanine and bis(tri-n-hexylsiloxy)silicon-2,3-naphthalocyanine are extremely strong amplifiers of the dimol emission. This shows that phthalocyanines and naphthalocyanines might be used for luminescence detection of monomols and dimols of singlet oxygen in systems of biomedical importance.