2-PHOTON EXCITATION OF ALKYL-SUBSTITUTED MAGNESIUM PHTHALOCYANINE - RADICAL FORMATION VIA HIGHER EXCITED-STATES

The photophysical properties of tetra-(tert-butyl)-phthalocyanato-magn esium (t4-PcMg) in solution and micro-heterogeneous systems (liposomes and micelles) were investigated. Radical cation formation occurs in c hloroform during UV excitation in the presence of an electron acceptor (CBr4). The same result is achieved by two-step absorption in the sin glet manifold using pulsed excitation at lambda(exc) = 670 nm, which i s of interest from the viewpoint of photon delivery through the therap eutic window of tissues. To obtain a deeper insight into the photophys ics leading to radical cation formation via the higher excited singlet state, the transient spectra and singlet-singlet absorption cross-sec tions were determined. In addition to strong excited state absorption within the spectral range of the Q(x)-band, relatively large absorptio n cross-sections were also found in regions with low ground state abso rption. The importance of these transitions for an effective two-colou r excitation regime is discussed with regard to new start mechanisms f or photodynamic laser tumour therapy.