Covalent nano-clip and nano-box compounds based on free base porphyrins

Novel nano-clip and nano-box compounds were obtained by reaction between dibromomethane and 5,15-di[p-(9-methoxytriethylenenoxy)phenyl]-10,20-di[p-hydroxyphenyl]porphyrin. The molecular architecture varies from a co-facial (nano-clip) to a four wall-box (nano-box) structure. The products were characterized by 1H NMR and UVevis spectroscopy and MALDI-TOF mass spectrometric analysis. The UVevis spectra of the nano-clip showed a modification of the characteristic porphyrin soret and Q bands, with respect to the monomer and cyclic tetramer, as a probable consequence of a hybrid orbital deformation (HOD) phenomenon involving the two porphyrin p rings forced to a closer co-facial spatial arrangement. The spatial distance between the two co-facial porphyrin units, and therefore the molecular cavity size, can be modified inducing an electrostatic repulsion by means of a reversible protonation of the pyrrolic cores. The 1H NMR spectra of the nano-box showed a strong high-field shift of some aromatic and ether protons present in the upper and lower rim of the molecular box.