Palladium porphyrin containing zirconium phosphonate Langmuir-Blodgett films

The substituted tetraphenylporphyrins palladium 5,10,15,20-tetrakis(2',3',5 ',6'-tetrafluorophenyl-4'-octadecyloxyphosphonic acid)porphyrin (16) and pa lladium 5,10,15-tris(2',6'-dichlorophenyl)-20-(2',3',5',6'-tetrafluoropheny l-4'-octadecyloxyphosphonic acid)porphyrin (17) have been studied as Langmu ir monolayers and as zirconium phosphonate Langmuir-Blodgett (LB) films. Us ing a three-step deposition technique, symmetric and alternating zirconium phosphonate bilayers and multilayers were prepared. In these films, the por phyrin constituent resides in the hydrophobic region of the monolayer and t he phosphonate substituents bind zirconium ions in the hydrophilic part. Fi lms of the pure porphyrins and of mixtures with octadecylphosphonic acid (O PA) were prepared. Langmuir monolayers were characterized with pressure vs area isotherms and reflectance UV-vis spectroscopy. LB films were studied w ith transmittance UV-vis and X-ray diffraction. Control over chromophore in teraction was achieved by chemical modification of the amphiphiles and by s election of appropriate transfer conditions. For example, reduced aggregati on was seen in LB films of the tetraphosphonic acid substituted porphyrin 1 6 transferred at mean molecular areas (MMA) larger than the area per molecu le of the substituted porphyrin. In these films, the porphyrin macrocycles are nonaggregated and oriented parallel to the surface. In contrast, the mo nophosphonic acid substituted 17 aggregates under all of the deposition con ditions studied. The stability of the porphyrin LB films was examined by ex posing the films to refluxing chloroform. UV-vis absorbance after immersion in chloroform confirmed conclusions that in films of 17, many of the chrom ophores are not tethered to the inorganic network and are easily removed, w hereas in films of 16, all molecules bind to the zirconium phosphonate exte nded network, making these films very resilient.