Bis-porphyrinic clamp for photo- and electro-active guests: a spectroscopic and photophysical study

The spectroscopic and photophysical characterization of a V-shaped Zn(II) b is-porphyrinic structure, ZnH, its free-base analogue FBH and the model por phyrin components ZnB and FBB is presented. With respect to the unsubstitut ed zinc porphyrin Zn, asymmetric substitution with tetraazaanthracene is re sponsible for the increase of dipole moment in the excited state of Zn(II) derivatives. The charge transfer character of the transition causes a remar kable solvent effect on the luminescence properties. Axial complexation of the zinc ion in ZnB and ZnH by pyridine induces a strong perturbation of th e photophysical properties. In the free base derivatives FBB and FBH the su bstituent displaces the equilibrium population with respect to unsubstitute d FB, on both the ground and excited states of the two tautomers, allowing for the presence of two independent populations (ca. 90% and 10%) of distin ct species detected by UV-Vis spectroscopy. The data are supported by semie mpirical calculations.