Metal-ions linked surface-confined molecular dyads of Zn-porphyrin–metallo-terpyridine: an experimental and theoretical study

Covalently-assembled monolayers of functionalized Zn-porphyrin complex (5,10,15,20-tetra(4-pyridyl)-porphyrin, Zn-TPyP) are employed as the template layer for fabricating heterogeneous molecular dyads composed of opto-active metallo-terpyridyl complexes on SiOx substrates. Metallo-linkers such as Cu2+ and Pd2+ are exploited to connect the Zn-porphyrin template layer with the metallo-terpyridyl complexes (M-PT, M = Fe2+, Ru2+, Os2+, while PT = 40-pyridyl terpyridyl) using a wet chemical "layer-by-layer" (LBL) technique. Formation of both the template and dyad layers over the SiOx substrates were probed by atomic force microscopy (AFM) and UV-vis absorption techniques. The molecular films were used for comparison and to study the effect of different metallo-linkers based on the changes in the characteristics of the Soret bands of Zn-TPyP and the metal-to-ligand charge-transfer (MLCT) bands of terpyridyl complexes. Besides, detailed electronic structure calculations based on first-principles density functional theory (DFT) and time-dependent DFT (TDDFT) have been performed for understanding experimentally observed photophysical properties of the surface-confined dyads.