LASER DESORPTION FOURIER-TRANSFORM MASS-SPECTROMETRIC STUDY OF PORPHYRINS ATTACHED TO HYDROCARBON SPACERS

The 248 nm laser desorption Fourier transform ion cyclotron resonance positive- and negative-ion mass spectra are presented for two novel porphyrin-spacer-quinone bichromophoric systems in which the spacer consists of a polynorbornyl-type hydrocarbon and also for a model tetraphenylporphyrin compound. The compounds are 1,2,3,4-tetrahydro-1,4-methano-7,10,13,16-tetraphenylbenzo[g]quinoxalino[2,3-b]porphyrin, 5,20-dihydro-5,20-methano-1,4-dimethoxy-8,11,14,17-tetraphenylnaphtho[2,3-g]quinoxalino[2,3-b]porphyrin and 5,10,15,20-tetraphenylporphyrin. The two-step laser desorption multiphoton ionization mass spectra recorded at laser powers < 2 MW cm-2 produce only the parent ions M+. and M-.. At increased laser powers of up to 5 MW cm-2 the [M + H]+ and [M - H]- ions are observed to increase significantly in relative abundance. At laser powers > 8 MW cm-2 the porphyrins show extensive photodissociation and rearrangement and, in one case, the production of an extensive distribution of carbon cluster fragment ions including the fullerene [C60]+..