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‐l,4‐dimethoxy‐8,11,14,17‐tetrapherylnaphtho [2,3‐ g ]quinoxalino[2,3‐b] porphyrin and 5,10,15,20‐tetraphenyl‐porphyrin. 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 [C 60 ] + ˙.