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.