Laser-Desorption Supersonic Jet Spectroscopy of Phthalocyanines

The laser-induced fluorescence excitation spectra of zinc phthalocyanine, chloroaluminum phthalocyanine, magnesium phthalocyanine, and free-base phthalocyanine have been investigated under jet-cooled conditions, by using pulsed infrared laser desorption as the means of vaporization. Assignment of the observed vibronic transitions reveals that many of them gain intensity from coupling of the S1(Q) state with the S2(B) and Q' states. Low-frequency out-of-plane modes of the macrocycle are observed in the region below 100 cm-1; the vibronic structure in this region of the spectrum is sensitive to deviation of the molecule from a planar geometry. The S1-S0 excitation energy shows a weak dependence on the hole size of the macrocycle. Copyright 1999 Academic Press.