A time-dependent density functional study of a non-aromatic [1.1.1.1.1]-pentaphyrin and its lutetium complex.

The molecular structures and absorption electronic spectra of two novel phototoxic pentapyrrolic expanded porphyrins (a isopentaphyrin derivative and its lutetium complex) have been studied at the density functional level and its time-dependent extension (TDDFT). The geometries were optimized with three different exchange-correlation functionals (PBE0, B3LYP, and ωB97XD) and the SV(P) basis set plus the pseudopotential method for the complex. With respect to the porphyrin, the structure of [1.1.1.1.1]-pentaphyrin and its lutetium complex are predicted much distorted due to the lack of conjugation. The lowest excitation energy band (experimental at 814 nm) for the free-base isopentaphyrin is well predicted by the ωB97XD at 772 nm. The possible photodynamic reaction mechanisms (types I and II) were studied through the calculation of the electron affinity and ionization potentials in solvent, using the COSMO model.