LANGMUIR-BLODGETT-FILMS OF AMPHIPHILIC PUSH-PULL PORPHYRINS

A series of nitrophenyl-amidophenyl-substituted porphyrins with n-C17H 35 tails have been synthesized and fully characterized. Good Langmuir- Blodgett films of these materials can be prepared on water and transfe rred successfully to glass slides. Mean molecular areas for the series were measured and found to increase from 80 to 230 Angstrom(2) as the number of aliphatic chains increased from one to four. As determined by linear dichroic measurements, this change in area does not correspo nd to a change in the orientation of the porphyrin with respect to the surface. In the absence of the steric constraints of multiple aliphat ic chains, porphyrin-porphyrin stacking permits close packing of the r ings. As the number of aliphatic chains on the porphyrin periphery inc reases, however, the porphyrin planes must pack more loosely. Thus, th e porphyrin macrocycle orientation is determined by interactions betwe en porphyrin rings and between porphyrins and the aqueous (or polar gl ass) surface. In contrast, the differences in the observed mean molecu lar area are determined independently by packing constraints imposed b y the pendant hydrocarbon chains.