Multiporphyrin Array from Interfacial Metal-Mediated Assembly and Its Langmuir-Blodgett Films

The Cd²⁺-mediated assembly of multiporphyrin arrays at air-subphase interfaces has been studied. Surface pressure-area isotherms for the monolayers of zinc tetrapyridylporphyrin (ZnTPyP) showed that the mean ZnTPyP molecular area was 0.65 and 1.9 nm2 on water and 0.1 M Cd²⁺ subphase surfaces, respectively. Spectroscopic measurements indicated that absorption of the ZnTPyP Soret band was 11 nm redshifted in the monolayer of the Cd²⁺-ZnTPyP multiporphyrin array, but 23 nm redshifted in the ZnTPyP monolayer, and that the Cd²⁺-linked network structure of the multiporphyrin array was retained after its monolayerwastransferred onto a solid plate. Similar orientation angles between themeanporphyrin plane and the substrate surface were measured for the Langmuir-Blodgett (LB) films of either Cd²⁺-ZnTPyP multiporphyrin arrays or ZnTPyP. On the basis of these results, we developed schematic models of the monolayers or LBfilms ofCd2+-ZnTPyP multiporphyrin arrays and ZnTPyP aggregates.Anemission spectral comparison between the LB film of ZnTPyP and that of the Cd²⁺-ZnTPyP multiporphyrin array indicated a significant quenching in the former case, due to the formation of ZnTPyP aggregates, but not in the Cd²⁺-ZnTPyP multiporphyrin array, the observation of which strongly supports our schematic models.