Bis-porphyrin clamp for photo- and electroactive guests for light energy conversion: a spectroscopic and photophysical study

<p> The spectroscopic and photophysical characterization of a V-shaped Zn(II) bis-porphyrinic structure, <strong>ZnH</strong>, its free-base analogue <strong>FBH</strong> and the model porphyrin components <strong>ZnB</strong> and <strong>FBB</strong> is presented. With respect to the unsubstituted zinc porphyrin <strong>Zn</strong>, 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 <strong>ZnB</strong> and <strong>ZnH</strong> by pyridine induces a strong perturbation of the photophysical properties. In the free base derivatives <strong>FBB</strong> and <strong>FBH</strong> the substituent displaces the equilibrium population with respect to unsubstituted <strong>FB</strong>, on both the ground and excited states of the two tautomers, allowing for the presence of two independent populations (<em>ca</em>. 90% and 10%) of distinct species detected by UV-Vis spectroscopy. The data are supported by semiempirical calculations. </p>