Electronic Laser Photodissociation Spectroscopy of Gas-Phase Metalloporphyrins and Metalloporphyrin-Aromatic Molecule Complexes

Metal containing porphyrins are found in crude oil at concentrations of 100-1000 PPM. Their presence can pose a challenge to petroleum chemistry as they poison hydrocarbon cracking catalysts, complicating the upcycling of heavy, long-chain petroleum. In this thesis, the electronic spectroscopy and photochemistry of isolated, gaseous metalloporphyrins, along with measurements for gas-phase metalloporphyrin-aromatic molecule complexes is studied. The electronic spectroscopic properties of; iron, nickel and vanadium tetraphenyl porphyrin, as well the unmetallated tetraphenyl porphyrin and hemin are studied, to provide information on how the metal centre and functional groups influence the intrinsic electronic spectra. In particular, the position, width and intensity of the two key porphyrin absorption bands, the “Soret” and Q bands is explored. Further experiments focus on metalloporphyrin-aromatic molecule clusters (e.g. pyridine and quinoline) to probe the effect of direct axial coordination to the metal centre on the electronic spectrum. The gaseous metalloporphyrins and their clusters have been studied in a novel custom-adapted laser-interfaced commercial mass spectrometer, where they are produced via electrospray ionization, mass-selected and then subjected to laser photoexcitation within a quadrupole ion trap, allowing the photochemistry to be monitored as a function of excitation wavelength. The results presented in this work represent the first direct measurements of the photodegradation pathways of metalloporphyrins and their complexes.