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) bis-porphyrinic structure, ZnH, its free-base analogue FBH and the model porphyrin components ZnB and FBB is presented. With respect to the unsubstituted zinc porphyrin Zn, asymmetric substitution with tetraazaanthracene is responsible for the increase of dipole moment in the excited state of Zn(II) derivatives. The charge transfer character of the transition causes a remarkable solvent effect on the luminescence properties. Axial complexation of the zinc ion in ZnB and ZnH by pyridine induces a strong perturbation of the photophysical properties. In the free base derivatives FBB and FBH the substituent displaces the equilibrium population with respect to unsubstituted 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 distinct species detected by UV-Vis spectroscopy. The data are supported by semiempirical calculations.