LANGMUIR-BLODGETT-FILMS OF STEARIC-ACID CONTAINING -TETRAKIS(((EICOSANYLOXY)CARBONYL)PHENYL)PORPHYRIN

Molecular mechanics calculations are coupled with a knowledge of prope rties of porphyrins in solution and available synthetic strategies to computer-designed a lipoporphyrin, -tetrakis(((eicosanyloxy)carbonyl)p henyl)porphrin] (LipoP), for future electron-transfer studies and bios ensor applications. To prevent separation of the porphyrin and stearic acid phases in the films, the head group was chosen on the basis of e arlier studies that showed that its nickel(II) derivative does not pi- pi aggregate in aqueous solution. The lack of aggregation of the porph yrin unit results from the high degree of nonplanarity of the macrocyc le and the steric constraints of the twelve bulky peripheral acid subs tituents. Nonpolar tails consisting of 20-carbon long linear alkanes w ere attached to the head group to anchor the LipoP head group into the stearic acid films. Metal derivatives of LipoP have been synthesized and characterized by NMR, resonance Raman, and UV-visible spectroscopi c methods. Also, the solubility and solution aggregation properties of LipoP were investigated. Finally, Langmuir films of the Ni derivative of LipoP in stearic acid (Sh) (and for comparison also films of nicke l protoporphyrin dimethyl ester (PPDME) in SA) were fabricated and cha racterized by pressure-area isotherms and then transferred as Langmuir -Blodgett (LB) films onto glass or silicon substrates. These NiLipoP-S A and NiPPDME-SALB films were characterized by spectroscopic methods. Resonance Raman spectra show that NiLipoP does not pi-pi aggregate in the films, unlike NiPPDME. Molecular mechanics calculations of the int eractions between NiLipoP, a stearic acid monolayer, and surrounding w ater molecules support a structural interpretation of the spectral and physical properties of the NiLipoP-SA films that locates the porphyri n head group outside of the hydrophobic region of the films while rema ining anchored into the film by the four attached hydrocarbon chains.