Mass spectrometry and laser photodissociation spectroscopy of gas-phase metalloporphyrin complexes, metalloporphyrin radicals, and Verteporfin

Metalloporphyrins are known for interacting with donor molecules via axial coordination and this ability to attach additional ligands determines their role in biological processes such as oxygen transport or enzyme catalysis. In addition, the introduction of donor
groups via ligation is being studied as a strategy for enhancing light-harvesting capacity and improving photovoltaic performance.
In this thesis, axial complexes between neutral metalloporphyrins and halide anions are studied in the gas-phase and their complexation energy determined with the aid of computational methods. The electronic properties and photochemistry of isolated gaseous zinc tetraphenyl porphyrin (ZnTPP) complexes with fluoride, chloride, bromide, and iodide are investigated using a novel custom-adapted laser-interfaced commercial mass spectrometer to provide information on how the axial complexation influences their intrinsic electronic spectra relative to the position and width of the Soret band. These spectroscopic experiments performed on negatively charged complexes are of interest because their low vertical detachment energy (VDE) can be accessed by the UV range of the laser and electron transfer processes from halide to porphyrin can be observed. In addition, these results represent the first proof of halide coordination in the gas-phase with neutral metalloporphyrin showing the formation of dimers and bridged complexes.
Further experiments involved the generation of ZnTPP and nickel octaethylporphyrin (NiOEP) radical cations and anions with electrospray ionization (ESI) and LDI
techniques. This work reports the first gas-phase absorption spectra of metalloporphyrin radicals together with their thermal and photo-induced dissociation channels and, a new, serendipitous, preparation procedure was found for generating metalloporphyrin radical anions in the gas phase via the LDI technique.
The last set of experiments presented in this thesis focuses on verteporfin (trade name Visudyne), a benzoporphyrin derivative photosensitizer used in photodynamic therapy of the treatment of the wet form of macular degeneration. In this work, the first direct study
of its photoproducts and photofragmentation channels in an organic solvent and in the gas-phase are presented together, along with the thermal dissociation products and the first gas-phase intrinsic absorption spectrum.