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Monolayers of surface-active hemicyanine dyes have been extensively studied owing in part to their potential importance for fabrication into non-linear optical materials. In an effort to increase the dipole moment to a value larger than that present in the typical hemicyanine, a neew compound was characterized, having the structure: (CH 3 ) 2 NC 6 H 4 CHCHCHCHC 6 H 4 N + C 22 H 45 B − which contains a more extended π-bonded system compared with some more commonly studied hemicyanines. It is known that hemicyanines may be present in various aggregated states as well as species having varying degrees of order when in monolayer form. For the new compound, monolayers could be produced having both ordered and disordered structures. On a pure water subphase, the new hemicyanine in a highly compressed monolayer had a narrow, blue-shifted absorption band with a maximum at 435 nm. Such a spectrum is characteristic of H-aggregate species. When the subphase contained cadmium chloride (1 × 10 −3 M) the optical absorption band was similar to that seen in chloroform solution for disaggregated species, with a broad absorption band at 485 nm, shifting only slightly as the monolayer was progressively compressed. Atomic force microscopy visualizing the two different films indicated that monolayers transferred from pure water subphase appeared inhomogeneous, discontinuous and indicative of island structures possibly in the original spread monolayer, or formed during transfer. Monolayers formed on Cd 2+ -containing subphases were uniform except for some small surface defects.

Monolayer characteristics were determined for three isomeric cleavable phospholipids containing a ketal group on one of the alkyl chains: 1-octadecanoyl-2-[ trans -[8-(2,2-dimethyl-5-octyl-1,3-dioxolan-4-yl)octanoyl]]- sn -glycero-3-phosphatidylcholine ( 1a ); 1-octadecanoyl-2-[16-(2,2-dimethyl-1,3-dioxolan-4-yl)hexadecanoyl]- sn -glycero-3-phosphatidylcholine ( 1b ); and 1-octadecanoyl-2-[ trans -[1-(2,2-dimethyl-5-pentadecyl-1,3-dixolan-4-yl)methanoyl]]- sn -glycero-3-phosphatidylcholine ( 1c ). the monolayer characteristics were also determined for two of the daughter surfactants in which a vic -diol group replaces the ketal group: 1-octadecanoyl-2-( threo -9,10-dihydroxyloctadecanoyl)- sn -glycero-3-phosphatidylcholine ( 2a ) and 1-octadecanoyl-2-(17,18-dihydroxyoctadecanoyl)- sn -glycero-3-phospha-tidylcholine ( 2b ). Surfactants 1a-c displayed surprisingly high solubility in the water subphase; stable monolayers could not be formed even at 7–8 °C. Reproducible surface pressure isotherms were obtained for 1a-c, 2a and 2b v using a subphase of aqueous 30% polyethylene glycol. The apparent areas/molecule were larger than expected based on estimates from CPK models, even assuming that all alkyl chains are flat on the interface and are never elevated above it to any appreciable degree, even at high compressions. Surface potential measurements generally remained constant throughout the range of compression. The disparities between measured and estimated molecular areas are probably due to two effects: chirality in the systems and occlusion of void areas present in many of the planar conformational states.

Neutron and X-ray reflection measurements and surface pressure isotherms of spread films of the fullerene—dodecylamine adduct C60[NH2(CH2)11CH3]x all indicate that this material may form monomolecular layers on water surfaces. The reflection data sets (neutron on both H2O and D2O) can be accounted for by a single model structure defined in terms of the dimensions of an average cell and its chemical composition. This model ascribes a total thickness of about 29 A to the molecular interface layer with the following internal structure. The fullerenes (with several alkyl chains attached) form a central stratum and the remainder alkyl tails are located close to both the air and water interfaces. The alkyl moieties close to the aqueous substrate are hydrated. The reflection experiments and the isotherms suggest that on average 8 ± 3 dodecylamine molecules are present per fullerene, consistent within error, with elemental analysis 5 ± 2. By contrast, neutron reflection and surface pressure vs. area data of spread films of C60 fullerenes on aqueous surfaces indicate the formation of inhomogeneous multilayer films with a thickness and a surface roughness exceeding the molecular size. These underivatized fullerenes thus do not form monomolecular films.

A series of electrochemical and Raman studies were undertaken to investigate the effects of orientation of electroactive species on their electrochemical behavior. Raman, resonance Raman, surface-enhanced Raman scattering, and surface-enhanced resonance Raman scattering techniques provided information essential for determining species orientation on electrode surfaces. The paradigm compounds employed were a series of derivatized viologens. Synthesis of these compounds involved the incorporation of long alkyl chains, rendering them surface-active and capable of incorporation into various kinds of oriented systems at interfaces. Orientation control was effected by the use of three techniques which provided a hierarchy of progressively more stringently oriented systems. Viologens were incorporated into vesicles, spontaneously self-assembled systems, and Langmuir-Blodgett (LB) monolayer arrays. Whereas the ordering and orientation control was probably least effective in vesicles, a maximal ordering could be attained in LB systems. Analysis of the experimental findings indicates that the systems studied show varied behavior and a complex interaction of the important variables operative during electrochemical processes. The extent of orientation present in specific preparations, the electrochemical potentials, the presence of counterions, the density of monolayer packing, and the exact structures (relative contributions of alkyl chains and of the viologen moiety) were all found to influence the behavior observed.

Surface pressure-area isotherms were established for a series of seven derivatized phthalocyanine compounds containing from one to four covalently linked macrocycles. Good solubility in spreading solvents was conferred by the presence of four neopentoxyl groups per macrocycle. All compounds studied formed strong, stable monolayers with high breaking pressures (about 50 mN m−1 or greater). Observed surface pressure-area isotherms were of the most simple kind, with no indication of phase transitions or discontinuities, with one exception. Minimal molecular areas were seen at lowest compression rates and higher temperatures, indicating that these systems have a large number of configurational states which are not capable of restructuring quickly into a compact monolayer of highest density. For some compounds it appears that orientation on the water surface can be essentially flat. Most previously studied phthalocyanine monolayers suggest that the macrocycles tend always to orient edge-on at some acute angle to the water surface because of the very strong cofacial energies of interaction. With other compounds of this group, it is evident that the macrocycles can assume orientations either parallel or perpendicular to the surface, others having intermediate orientations as well. In addition, one multinucleate compound probably assumes a bilayer structure at high surface pressures. The range of orientations available in these systems should appreciably extend the utility of phthalocyanines in monolayers transferred by the Langmuir-Blodgett technique. The present study indicates that a more complete exploitation of the possibilities of organic synthesis can result in a more varied monolayer behavior than seen hitherto.

Results of film compression studies on monolayers of di(2-ethylhexyl)phosphate (HDEHP) and other alkyl phosphoric acid derivatives are reported. HDEDP was found to form coherent monolayers below room temperature with apparent molecular areas which progressively decreased with increasing cycles of compression. Marked hysterisis was noted upon expansion and recompression of a compressed film. Expanded layers of HDEHP were found to gradually lose coherency and become destructured if left expanded for hours or days. This behavior was attributed to molecular disengagement due to weakly interacting alkyl chains and the presence of chain branching. Results of studies of other alkyl phosphoric acid derivatives indicate similar behavior, but the consequences of branching were apparently more important than the physical state (solid or liquid) of the monolayer. (BLM)