Multiporphyrin array from interfacial metal-mediated assembly and its Langmuir-Blodgett films

The Cd2+-mediated assembly of multiporphyrin arrays at air-subphase interfa ces 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 nm(2) on water and 0.1 M Cd2+ subphase surfaces, resp ectively. Spectroscopic measurements indicated that absorption of the ZnTPy P Soret band was 11 nm redshifted in the monolayer of the Cd2+-ZnTPyP multi porphyrin array, but 23 nm redshifted in the ZnTPyP monolayer, and that the Cd2+-linked network structure of the multiporphyrin array was retained aft er its monolayer was transferred onto a solid plate. Similar orientation an gles between the mean porphyrin plane and the substrate surface were measur ed for the Langmuir-Blodgett (LB) films of either Cd2+-ZnTPyP multiporphyri n arrays or ZnTPyP. On the basis of these results, we developed schematic m odels of the monolayers or LB films of Cd2+-ZnTPyP multiporphyrin arrays an d ZnTPyP aggregates. An emission spectral comparison between the LB film of ZnTPyP and that of the Cd2+-ZnTPyP multiporphyrin array indicated a signif icant quenching in the former case, due to the formation of ZnTPyP aggregat es, but not in the Cd2+-ZnTPyP multiporphyrin array, the observation of whi ch strongly supports our schematic models.