A comparative study of two-photon properties of zinc(II)-porphyrin, meso-meso singly-linked zinc(II)-diporphyrin and zinc(II) meso,meso-coupled porphyrin dimer via hydrogen bonding interactions

Electronic structures, one- and two-photon absorption (TPA) properties of zinc(II)-porphyrin compound (ZH), meso-meso singly-linked zinc(II)-diporphyrin compound (Z2H) and zinc(II) meso,meso-coupled porphyrin dimer (Z2H-G) via intermolecular hydrogen bonding interactions have been comparatively studied by using ZINDO-SOS method. The results show that formation of hydrogen bondings between carboxyl groups and cyclic urea reduces the dihedral angle between the adjacent porphyrin planes in Z2H-G, leading to increased electronic interactions between the two porphyrin planes and increased couplings between electronic states. Electronic spectrum of ZH can be described with the four-orbital model, while the descriptions of the electronic spectra of Z2H and Z2H-G need eight frontier orbitals. Theoretical calculations reveal that TPA cross sections increase on going from ZH to Z2H to Z2H-G due to increase of the couplings between electronic states through transition dipole moments.