Supermolecular Engineering at the Air-Water Interface: Spatially Controlled Formation of Heterodimers from Amphiphilic Porphyrins and Porphyrazines through Specific Molecular Recognition
Résumé
Mixed films built from two different tetrakissubstituted amphiphilic porphyrinic macrocycles and their copper(I1) derivatives are reported: the equimolar mixture of tetrakis[4-[( 1 -carboxyhenicosyl)oxy]phenyl]porphine (PI) and tetrakis(3-docosylpyridin0) porphine tetrabromide (P2) (the [PI + P2] mixed film) and the equimolar mixture of PI and tetraoctadecyltetrapyridinoporphyrazinium tetrabromide (P3) (the [PI + P3] mixed film). Flat-lying heterodimers PI-PI and P,-P3 are spontaneously formed at the air-water interface via an acido-basic reaction between the four functional groups of each macrocycle. The formation of the heterodimers and the geometry taken within each heterodimer are examined by spectroscopic measurements on the resulting LB films built-up either as homolayers or as alternated layers with an amphiphilic cyclodextrin (CD) as spacer. Infrared spectra allow us to check the formation of an ionic bond between the carboxylate functions of PI and the pyridinium groups of P2 and P3. ESR spectroscopy on alternated LB films [CUP, + Cup21 llCD and [CUP,+ Cup3]l lCD gives rise to a well-resolved C U 'WUd~im~e ric signal. Finally, the ESR study on homolayers built from the monocopper mixtures ([CUP, + H2P2] or [H2PI + CuP2]) provides clear evidence on the actual location of each macrocycle within the heterodimer: PI lies above P2 or P3. This geometry is confirmed by redox phenomena observed in the [PI + P,] mixed films. Thus, designed supermolecular assemblies can be built through the geometrical control of intermolecular interactions at the air-water interface. This general strategy provides an elegant and efficient access toward molecular machines